XIIIth International Symposium on Nuclear Symmetry Energy (NuSym25)

8 Sept 2025, 09:00 → 13 Sept 2025, 13:00 Asia/Tokyo

Auditorium (8F) (Integrated Innovation Building (IIB), RIKEN Kobe Campus)

Akira Ono (Tohoku University), Juzo ZENIHIRO (Department of Physics, Kyoto University), Kenichi Yoshida (The University of Osaka), Mizuki Kurata-Nishimrua (RIKEN), Natsumi Ikeno, Tadaaki Isobe (RIKEN), Tomoya Naito (RIKEN iTHEMS), hajime sotani (RIKEN)

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[Important Announcement]

• 2025-09-01: We decided the registration fee for students is waived.
• 2025-08-28: Timetable is announced
• 2025-08-20: Abstract submission for the poster presentation is closed.
• 2025-07-30: Early registration is closed, but the registration is still open.
• 2025-07-25: Abstract submission for the poster presentation is still open!
• 2025-06-20: Abstract submission for the oral presentation is closed.
• 2025-05-07: Second circular is announced.
• 2025-02-07: First circular is announced.

Please ignore any emails regarding the workshop from travel agencies or other companies that are not from the organizers or RIKEN, as we do not request accommodation support from any company.

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[Overview]

The symposium will address experimental and theoretical investigations of the equation-of-state (EoS) of nuclear matter at various isospin asymmetries. Such investigations include efforts in nuclear structure, nuclear reactions, and heavy-ion collisions, as well as astrophysical observations of compact stars and associated phenomena. An important role of the symposium is to unify the efforts of the nuclear physics and astrophysics communities in addressing common research challenges.

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[Topics of NuSym Symposium]

Topics of the NuSym symposium are related to nuclear equation-of-state (EoS) and symmetry energy in laboratory experiments, in astrophysical observations, and microscopic theories:

• Nuclear structure and reactions;
• Heavy-ion collision experiments and transport model simulations;
• Microscopic calculations of neutron-rich dense nuclear matter;
• Isospin and spin dependence of nuclear interactions and correlations;
• Clustering in isospin-asymmetric nuclear systems;
• Strangeness in nuclei and nuclear matter;
• Astrophysical multi-messenger observations and nucleosynthesis;
• Theory of compact stars, including neutron star mergers and supernovae;
• Future experiments and facilities.

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[Schedule of NuSym Conference]

• NuSym Scientific Session: 08–12 September 2025
• Transport Model Evaluation Project (TMEP): 12–13 September 2025

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[Important Dates]

• Abstract Submission Deadline: 20 June 2025 (Closed)
• Registration Deadline with Visa Documents: 30 July 2025 (Closed)
• Early Payment Deadline: 30 July 2025 (Closed)
• Abstract Submission Deadline for Poster Presentation: 20 August 2025 (Closed)
• Registration Deadline: 30 August 2025 (Closed)

Please note that it takes approximately seven working days to prepare the visa application documents. The preparation of visa documents will begin on 15 June.

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This conference is supported by

• RIKEN Nishina Center for Accelerator-Based Science
• RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences
• JST ASPIRE: RIKEN-Berkeley Mathematical Quantum Science Initiative
• Research Center for Nuclear Physics, The University of Osaka

Circulars

• 10_Excursion.pdf
• First Circular
• Second Circular

Monday 8 September

09:00 Morning Coffee

NuSym Scientific Session: Session 1

Convener: Tadaaki Isobe (RIKEN)

1 Opening

Speaker: Tadaaki Isobe (RIKEN)

opening.pdf

2 The overview of theoretical study for nuclear EOS

In this talk, I will give an overview of theoretical study for nuclear EOS, especially for the symmetry energy, mainly including recent progresses from nuclear structures (nuclear ground state masses, nuclear giant resonances, and nuclear neutron skin), heavy-ion collisions (particle production and flows based on the advanced transport models) and neutron star observations (mass, radius, tidal polarization from gravitational wave signal of binary neutron star merger, and hyperon effects – hyperon puzzle).

Speaker: Lie-Wen Chen (Shanghai Jiao Tong University, Shanghai, China)

2509NuSym-Lie-Wen_Chen.pdf

3 Overview of recent experimental study towards determination of nuclear EoS

This presentation provides an overview of recent experimental efforts to constrain the nuclear equation of state (EoS), with a particular focus on the density dependence of the symmetry energy. A broad range of measurements, spanning beam energies from a few MeV/nucleon to a GeV/nucleon, will be discussed. These experiments probe different density regimes, from sub-saturation to supra-saturation, through a variety of isospin-sensitive observables.
Key observables include isospin diffusion, neutron-to-proton and triton-to-3He yield ratios, collective flow, charged pion production, cluster production, and pygmy dipole resonances (PDRs). Special emphasis will be placed on the interplay between neutron skin thickness, cluster formation, and PDRs, which provides powerful and complementary constraints on the slope parameter L of the symmetry energy at sub-saturation densities. Results from major experimental campaigns, including ASYEOS, INDRA-FAZIA, FOPI, SπRIT, and FRIB, will be presented, along with recent advances in detector systems and data analysis techniques. The role of current and future facilities: FRIB, FAIR, RIKEN, and SPIRAL2/GANIL, in enabling precision measurements across a wide range of isospin asymmetries will also be highlighted.
Together, these experimental efforts are instrumental in reducing uncertainties in the nuclear EoS and symmetry energy, and they provide critical guidance for theoretical modeling. Ultimately, they contribute to a unified understanding of asymmetric nuclear matter with far-reaching implications for both finite nuclei and astrophysical objects such as neutron stars and core-collapse supernovae.

Speaker: Dr Abdou Chbihi (GANIL)

NuSym2025ExpReviewAChbihi.pdf

10:50 Coffee Break

NuSym Scientific Session: Session 2

Convener: Dr Mizuki Kurata-Nishimrua (RIKEN)

4 Overview: EOS of Neutron-Rich Matter from Observations of Neutron Stars

Understanding the nature of dense neutron-rich matter and determining its Equation of State (EOS) remain fundamental goals in both nuclear physics and astrophysics. Among the components of the EOS in neutron-rich matter, the nuclear symmetry energy—which quantifies the energy cost of converting protons into neutrons in nuclear matter—remains the most uncertain. This symmetry energy plays a pivotal role in determining the composition, phase structure, dynamics, and static properties of neutron stars, as well as the strain amplitudes and frequencies of gravitational waves emitted during their mergers.

Astrophysical observations of neutron stars, though often limited and affected by significant uncertainties, have imposed increasingly stringent constraints on the EOS of dense neutron-rich matter—particularly following the landmark detection of GW170817. Encouragingly, these observational constraints are generally consistent with those derived from terrestrial nuclear laboratory experiments.

In this invited overview—necessarily selective due to the limitations of both my knowledge and the available time—I will first revisit several long-standing issues in constraining the EOS of dense neutron-rich matter. I will then highlight recent advances, particularly in our understanding of the density dependence of the nuclear symmetry energy, and identify key challenges that remain. Finally, I will discuss the prospects, potential benefits, and limitations of future high-precision neutron star radius measurements from upcoming X-ray and gravitational wave observatories in further constraining the EOS of dense neutron-rich matter.

Speaker: Bao-An Li (East Texas A&M University)

BALI-NuSym25A.pdf

5 Role of the symmetry energy on hybrid stars

Neutron stars are laboratories for the properties of
supra-dense matter and large isospin asymmetries, requiring expertise
from nuclear physics, particle physics, and astrophysics. Terrestrial
experiments are complementary since they probe the properties of
supra-dense matter close to nuclear saturation density (the average
density of atomic nuclei), or above but remaining close to isospin
symmetry. Since it connects isospin symmetric matter from terrestrial
experiments to neutron-rich matter in neutron stars, the symmetry energy
is instrumental. In this talk, I will present a theoretical approach
that can be employed to describe the properties of atomic nuclei and the
astrophysical observations, e.g., gravitational waves (LVK) and x-ray
emission from multi-second pulsars (NICER).
The impact of the symmetry energy on compact stars' properties is then
analyzed considering constraints from nuclear physics and astrophysics.
A compact star can be a neutron star composed only of nuclear matter or
a hybrid star with a quark core. Two typical models (soft and stiff) are
considered for the nuclear equation of state, and for the hybrid's one,
a parameterized first-order phase transition approach, completed with a
linear quark matter equation of state, is implemented.
In this talk, I will show that the phase transition reduces the tension
between GW170817 and NICER observations, and I will illustrate the
impact of the symmetry energy for the understanding of the nature of the
binary system in GW170817, confirming previous findings that the
GW170817 waveform is best described as a binary HS with stiff quark
matter at low density. This could also mark the presence of a quarkyonic
cross-over.

Speaker: Jérôme Margueron (International Research Laboratory on nuclear physics and nuclear astrophysics)

2025-09-NuSym25-Margueron.pdf

12:30 Lunch and Coffee

NuSym Scientific Session: Session 3

Convener: Kenichi Yoshida (The University of Osaka)

6 Role of the isovector spin-orbit potential in mitigating the CREX-PREX dilemma

The CREX-PREX dilemma involving the weak form factors of calcium-48 and lead-208 challenges models that tie neutron skins to the symmetry energy. We explore a resolution by artificially enhancing the isovector spin-orbit interaction in relativistic mean-field models. This adjustment brings theoretical predictions into agreement with experiment by modifying the neutron distribution in calcium, while leaving lead largely unaffected. However, it disrupts spin-orbit shell structure and magic numbers, suggesting that although promising, this approach may not be the full solution.

Speaker: Dr Marc Salinas (Lawrence Livermore National Laboratory)

NuSym Talk.pdf

7 Bayesian and frequentist model comparison for nuclear symmetry energy

Model dependence is a common issue in nuclear physics, especially when extracting physical information from data using theoretical models. In recent years, the quantification of inter-model uncertainties has received increasing attention. In this talk, I will introduce methods for model averaging and model selection within both Bayesian and frequentist frameworks, and demonstrate their application to the study of the nuclear symmetry energy.

Speaker: zhen zhang

ZhenZhang_NuSYM25.pdf

8 Equation of state of spin-polarized nuclear matter in the relativistic Hartree-Fock method

We calculated the equation of state (EOS) of spin-polarized nuclear matter in the relativistic Hartree-Fock method. To this end, we employed the relativistic point-coupling model, with which the Fock terms are considerably simplified, reducing them to the same form as the Hartree terms. In analogy to the slope parameter $L$ of the isospin-symmetry energy for spin-unpolarized matter, we evaluated the spin slope parameter $L_s$ of the corresponding spin-symmetry energy for spin-polarized matter. We will show that the slope parameter $L$ and the spin slope parameter $L_s$ have a negative correlation in the case of isoscalar polarization, where neutrons and protons are spin-polarized in the same direction. On the other hand, the spin slope parameter $L_s$ is nearly independent of the slope parameter $L$ in the case of isovector polarization, where neutrons are spin-polarized along the opposite direction to protons. We will also show that these correlations are a natural consequence of the relativistic point coupling model which we employ.

Speaker: Toi Tachibana (Department of Physics, Kyoto University)

slide_2025_9_8.pdf

15:20 Coffee Break

NuSym Scientific Session: Session 4

Convener: Zhigang Xiaozg (Department of Physics, Tsinghua University)

9 Cluster correlations in heavy-ion collision simulations

Practical treatments of light cluster correlations in heavy-ion collision simulations and the clusters' potential in learning about bulk nuclear properties are reviewed. The difficulty in describing clusters in semiclassical approaches stems from the discrete nature of the clusters' spectra. The opportunity that the clusters represent, to learn about bulk nuclear properties, stems from a tighter relation of cluster velocity to production location than for nucleons or pions.

Speaker: Pawel Danielewicz (Facility for Rare Isotope Beams, Michigan State University)

tkko25.pdf

10 Alpha-removal amplitude including the finite-size effect of the alpha particle

Alpha clustering, which is prominently observed in light nuclei, also plays a significant role in the surface region of heavy nuclei. Recent studies have emphasized the correlation between alpha formation at the nuclear surface and the cross sections of alpha knockout reactions in Sn isotopes [1].
We previously proposed a method to evaluate the local alpha-removal strength using mean-field theory (Hartree-Fock + BCS), which is standard for heavy nuclei. In this approach, four nucleons with different spin and isospin are removed from the same spatial coordinate [2]. The local alpha-removal strength quantifies the alpha formation at a specific coordinate in the nucleus and enables the evaluation of transitions to both ground and excited states. However, this method assumes point-like alpha particles and does not account for rearrangement effects in the final state, leaving room for improvement.
In this study, we construct an alpha annihilation operator without assuming point-like particles, but assuming that the constituent nucleons distribute as the 0s orbital. Incorporating the finite size of the alpha particle allows us to separate its center-of-mass coordinate, leading to a more realistic evaluation of the alpha-removal strength.
We calculate the transition matrix elements of the alpha annihilation operator between the initial and final nuclear states, both obtained using Hartree-Fock-Bogoliubov theory. While the use of mean-field theory restricts the final states to ground states, it enables the inclusion of rearrangement effects in the final nucleus.
We will present results for several isotopes, including Sn isotopes, for which systematic measurements of alpha knockout cross sections have been reported.
[1] J. Tanaka et al., Science 371, 260 (2021).
[2] T. Nakatsukasa and N. Hinohara, Phys. Rev. C 108, 014318 (2023).

Speaker: Nobuo HINOHARA (Center for Computational Sciences, University of Tsukuba)

hinohara-nusym25.pdf

11 Polaron physics and nuclear symmetry energy in neutron star matter

The notion of polarons has been developed to describe in-medium impurity states and interaction effects in the context of condensed-matter physics. Recently it has also been realized in ultracold atoms, which can be regarded as an ideal platform for investigating many-body physics in nuclear matter. In this contribution, we discuss how the polaron properties established in condensed-matter systems can be applied to neutron star matter involving a lot of degrees of freedom such as spin, isospin, and multi-nucleon clusters. We also show the equivalence between a polaron energy of proton in neutron matter and the nuclear symmetry energy.

Speaker: Hiroyuki Tajima (The University of Tokyo)

tajima_NuSym25.pdf

Tuesday 9 September

09:00 Morning Coffee

NuSym Scientific Session: Session 5

Convener: Juzo ZENIHIRO (Department of Physics, Kyoto University)

12 Equation of State of Neutron Stars in the Era of Multi-Messenger Astronomy

TBA

Speaker: Ang Li (Xiamen University)

Nusym2025Ang.pdf

13 Investigating ultra-high-density equations of state through gravitational waves from binary neutron stars mergers

After an overview of the current status of astrophysical observations and numerical simulations of binary neutron star mergers, I will present our ideas on how to possibly discriminate equations of state (EOSs) with a quark-hadron crossover with respect to EOSs with purely hadronic matter or with a first-order quark-hadron transition through gravitational waves emitted in binary neutron star mergers.

Speaker: Prof. Luca Baiotti (The University of Osaka)

2025-09-09_International-Symposium-on-Nuclear-Symmetry-Energy_Kobe.pdf

14 Symmetry energy constrained by gravitational waves

In this talk, we discuss how the existing and future detection of the
gravitational waves from compact stars can help reduce the uncertainties
in the density dependence of the symmetry energy.

Speaker: Chang Ho Hyun (Daegu University)

nusym25-hyun.pdf

10:40 Coffee Break

NuSym Scientific Session: Session 6

Convener: Akira Ono (Tohoku University)

15 Nuclear clustering in dilute nuclear matter within time-dependent density functional approaches

Understanding many-body correlations in sub-saturated nuclear matter is essential for constructing a reliable equation of state (EOS), with wide-ranging implications in both nuclear and astrophysical contexts. At low densities, bound states of nucleons naturally emerge as a result of these correlations and are often treated phenomenologically within energy density functional (EDF) frameworks by introducing clusters as explicit degrees of freedom (DOF).

Recent EDF-based models have been extended to incorporate effective cluster DOF embedded in dense nuclear matter, informed by experimental evidence for nucleon-nucleon short-range correlations at higher densities. These developments allow for a unified treatment of correlated structures across a wide density range.

In this talk, we present new approaches to include light cluster DOF and their in-medium modifications at sub-saturation densities, within an upgraded time-dependent EDF framework. This enables the modeling of non-equilibrium processes relevant to heavy-ion collisions, particularly the formation of light nuclei and intermediate-mass fragments.

Our unified theoretical framework supports a more complete and consistent description of nuclear matter, bridging equilibrium and dynamical scenarios. By coupling these models to advanced transport simulations and Bayesian inference techniques, we aim to constrain the nuclear EOS using inputs from nuclear structure, reaction experiments, and astrophysical observations—including those related to compact stars and gravitational wave signals from binary mergers.

Speaker: Stefano Burrello (Laboratori Nazionali del Sud (INFN))

NuSYM25_Burrello.pdf

16 Probing Nucleon-Nucleon Short Range Correlations by Bremsstrahlung gamma-rays in Heavy Ion Collisions

Short range correlation (SRC) in nuclei refers to the nucleons forming temporally correlated pairs in close proximity, giving rise to the high momentum of the nucleons beyond Fermi surface. It has been reported that Bremsstrahlung gamma production from np process in heavy ion reactions provides a novel probe to the existence of SRC in nuclei. In this talk, I will present the first quantitative results of measuring the Bremsstrahlung gamma rays in $^{124}$Sn+$^{124}$Sn reactions at 25 MeV/u using the Compact Spectrometer for Heavy IoN Experiment (CSHINE). Two main methods are applied to subtract the background. By comparing the experimental gamma spectrum with the Isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) simulations, the ratio of the high momentum tail (HMT) arising from the SRC is extracted as $(20\pm7)\%$ is obtained at a $3\sigma$ confidence level.

Speaker: Zhigang Xiaozg (Department of Physics, Tsinghua University)

ZGXiao-Nusym2025.pdf

17 spin dynamics in intermediate-energy heavy-ion collisions

While the spin polarization of hyperons and the spin alignment of vector mesons become a hot topic in relativistic heavy-ion collisions, the spin dynamics in intermediate-energy heavy-ion collisions has attracted little attention. Starting from the spin-dependent Boltzmann-Vlasov equation, we have derived the spin-dependent equations of motion for nucleons, and developed a spin- and isospin-dependent Boltzmann-Uehling-Uhlenbeck transport model. It has been found that the nucleon spin polarization can be generated from either the spin-dependent mean-field potential or the spin-dependent nucleon-nucleon scatterings.

Speaker: Jun Xu (Tongji University)

spin dynamics_JunXu.pdf

12:30 Lunch and Coffee

NuSym Scientific Session: Session 7

Convener: Jérôme Margueron (International Research Laboratory on nuclear physics and nuclear astrophysics)

18 Ab initio calculation of Hyper-nuclear matter

The equation of state (EoS) of nuclear matter plays a decisive role to understand the neutron star properties and the gravitational waves from neutron star mergers. At sufficient densities, the appearance of hyperons generally softens the EoS, leading to a reduction in the maximum mass of neutron stars well below the observed values of about 2 solar masses. Even though repulsive three-body forces are known to solve this so-called ``hyperon puzzle'', so far performing ab initio calculations with a substantial number of hyperons for neutron star properties has remained elusive. Starting from the newly developed auxiliary field quantum Monte Carlo algorithm to simulate hyper-nuclear matter (HNM) without any sign oscillations, we derive three distinct EoSs by employing the state-of-the-art Nuclear Lattice Effective Field Theory. We include $N\Lambda$, $\Lambda\Lambda$ two-body forces, $NN\Lambda$, and $N\Lambda\Lambda$ three-body forces. Consequently, we determine essential astrophysical quantities such as the neutron star mass, radius, tidal deformability, and the universal $I$-Love-$Q$ relation. These predictions are in good agreement with the latest astrophysical constraints derived from observations of massive neutron stars, gravitational waves, and joint mass-radius measurements. Also, for the first time in ab initio calculations, we investigate both non-rotating and rotating neutron star configurations. The results indicate that the impact of rotational dynamics on the maximum mass is small, regardless of whether hyperons are present in the EoS or not.

Speaker: Hui Tong (University of Bonn)

HTong_20250909.pdf

19 Nuclear matter calculation based on self-consistent Green's function

Self-consistent Green's function (SCGF) simulations have been capable to provide useful insight into the structure of homogeneous nucleonic matter, in part dure to their ease in handling hard potentials and at finite temperature and in part thanks to the possibility for direct access to physical information such as response and nucleon mean free-path. There exists two different implementations of SCGF that either work directly in the thermodynamic limit or exploit discretised bases with periodic boundary conditions. This talk covers recent advances on both.

Simulations at the thermodynamic limit focus on resolving nucleon-nucleon short range correlations and are typically performed at finite temperature to avoid neutron-proton pairing instability. We proposed a new formulation of SCGF based on Nambu covariant perturbation theory that will allow embed finite temperatures, pairing and superfluidity on the same footing [1,2].

Conversely, discretised bases in periodic boundary conditions allow to exploit the more sophisticated many-body expansions that are normally employed only for finite nuclei. Within this framework, we have implemented the so-called algebraic diagrammatic construction at third order [ADC(3)] and combined it with a Gorkov 1^st order pairing [3]. In contrast to previous simulations at the thermodynamic limit, particle-hole response effects can be handled also at zero temperature. A recent benchmark shows consistency of this new approach with other ab initio simulations with the same periodic boundary conditions ansatz [4].

[1] M. Drissi, A. Rios and C. Barbieri, Ann. of Phys. 469, 169729 (2024).
[2] M. Drissi, A. Rios and C. Barbieri, Ann. of Phys. 469, 169730 (2024).
[3] F. Marino, C. Barbieri and G. Colò, in preparation (2025).
[4] F. Marino, W. G. Jiang and S. J. Novario, Phys. Rev. C 110, 054322 (2024).

Speaker: Prof. Carlo Barbieri (Università degli Studi di Milano and INFN Milano)

NuSym2025_Kobe_Barbieri.pdf

20 Constraints on the nuclear equation of state from astrophysical observations using relativistic mean-field models

Taking into account astrophysical observations of neutron stars, we present new effective interactions based on relativistic mean-field (RMF) models. In addition to the isovector-vector ($\vec{\rho}^{\,\mu}$) meson, the isovector-scalar ($\vec{\delta}$) meson and meson-mixing terms involving isoscalar and isovector mesons---specifically $\sigma^{2}\vec{\delta}^{2}$ and $\omega_{\mu}\omega^{\mu}\vec{\rho}_{\nu}\cdot\vec{\rho}^{\,\nu}$---are incorporated into conventional RMF models to investigate the properties of isospin-symmetric nuclear matter. The equations of states (EoSs) for neutron stars are constructed to satisfy precise measurements of neutron-star radii from the NICER mission, as well as the stringent constraint on tidal deformability from the binary neutron-star merger event GW170817. Our results show that recent neutron-star observations significantly affect the construction of nuclear EoSs, leading to a softening of the nuclear symmetry energy around twice the nuclear saturation density, primarily due to $\sigma$-$\delta$ mixing.
We also discuss properties of finite nuclei with a focus on the neutron skin thickness of $^{48}$Ca and $^{208}$Pb, in light of data from CREX and PREX2 experiments.

Speaker: Tsuyoshi Miyatsu (Soongsil University)

NuSym2025.T.Miyatsu.pdf

15:20 Coffee Break

NuSym Scientific Session: Session 8

Convener: Natsumi Ikeno

21 Systematic Study on Neutron-Skin Thickness for Ni Isotopes : An Approach to Constraining the Nuclear Equation of State

The equation of state (EOS) of nuclear matter is essential not only for describing the structure and collisions of atomic nuclei but also for understanding various astrophysical phenomena such as the mechanism of supernova explosions and the structure of neutron stars. The EOS includes components that depend on the difference between proton and neutron densities, which are represented by the symmetry energy. It has been shown that the first-order coefficient of the density dependence of the symmetry energy is closely related to the neutron-skin thickness, which is the difference between the neutron and proton distribution radii in nuclei[1].

In this study, we measured the interaction cross sections $\sigma_{\rm I}$ of $^{58-77}\mathrm{Ni}$ isotopes on a carbon target at 250 MeV/nucleon in order to determine the matter radius. These $\sigma_\rm I$ data constitute the first systematic dataset for the Ni isotope chain in this mass region. Using a modified Glauber model based on the optical limit approximation, we successfully extracted the RMS nuclear matter radii $\langle r^2 \rangle_\rm m^{1/2}$. By combining these results with charge radii previously measured via isotope shift methods, we derived the neutron-skin thickness $r_{\rm np}$. The measurement of charge radii using the isotope shift method has only been performed in the range of $^{58-68, 70}\mathrm{Ni}$[2], in which region the neutron skin thickness was derived in this work.

From the slope of the neutron-skin thickness as a function of the relative neutron excess $\delta$=(N−Z)/A, we extracted the EOS parameter L. The result was estimated as L=81(63) MeV, and this value is consistent with previous estimations[3,4]. In the future, precise measurements of the charge radii in the neutron-rich region of $^{71-77}\mathrm{Ni}$ are highly anticipated. These measurements are expected to enable the direct determination of neutron-skin thicknesses, and nuclear structure theories capable of reliably extracting the EOS parameter L from the resulting data are also eagerly awaited.

[1] M. Centelles et al., Phys. Rev. Lett. 102 (2009) 122502.
[2] S. Malbrunot-Ettenauer et al., Phys. Rev. Lett. 128 (2022) 022502.
[3] Bao-An Li et al., Phys. Lett. B 727 (2013) 276-281.
[4] Brendan T. Reed et al., Phys. Rev. Lett. 126 (2021) 172503.

Speaker: Miki Fukutome

22 Extraction of the matter density distribution and radius of 132Sn via proton elastic scattering at 200 MeV/nucleon

Nuclear radius and density distribution are fundamental quantities that characterize the ground-state properties. Proton elastic scattering at intermediate energies is a powerful method for deducing matter distribution. To extend this technique to radioactive isotopes (RIs), we have developed various experimental tools, including particle identification detectors for the RI beams, a solid hydrogen target, and a recoil proton spectrometer. Using these devices, we performed a proton elastic scattering experiment on the double magic nucleus, $^{132}$Sn at 200 MeV/nucleon at RIKEN RIBF. The neutron skin structure of $^{132}$Sn is known to have a strong correlation with the symmetry energy of nuclear matter, as that of $^{208}$Pb. However, its matter radius had not been measured prior to this study. In this presentation, we will report the details of the experiment and its results. In addition, we will discuss the matter distribution and radius of $^{132}$Sn, which were extracted for the first time by analyzing the obtained angular distribution of the cross-section using relativistic impulse approximation calculations.

Speaker: Yuto Hijikata (RIKEN)

NuSym2025HJKT.pdf

23 Neutrino process calculation for SiC presolar grains and meteorites

Some rare isotopes such as 7Li, 11B, 138La, and 180Ta are considered to be synthesized by neutrino-induced reactions in core-collapse supernovae (neutrino process). The study of the neutrino-process has an important tole for understanding neutrino physics such as neutrino mass hierarchies and explosion mechanism. Here we report the calculated results using the neutrino process in SNe [1].11B is predominantly produced from 12C in outer layers by both charged and neutral current reactions with neutrinos, and 7Li is predominantly produced from 4He in neutrino-process. In contrast, 138La is produced in the inner O/Ne/Mg rich layers. The neutrinos in 4He and 12C rich layers are affected by collective neutrino oscillation in proto-neutron star and MSW effect in outer layers, whereas neutrinos producing 138La in the O/Ne/Mg layers are only affected by the collective neutrino oscillation. Therefore, the abundance ratios of these isotopes give a hint to understand the collective neutrino oscillation. The isotopes ratios of 11B/10B and 7Li/6Lis in presolar grains originating from SNe have been reported. The calculated results shows that the observed ratios cannot be reproduced by standard model, suggesting mixing of intermediate material with SNe ejecta. We further calculated the correlation between 11B/10B (7Li/6Li) and 138La/139La. This shows the clear separation between both neutrino mass hierarchies. We further calculated the correlation between 138La/139La and 50Ti/48Ti, which has been measured in CAI formed in the early solar system formation. The results suggest that ejecta of a SNe contributed to the early solar materials.

[1] X. Yao et al. Astrophys. J. 980, 247 (2025).

Speaker: Takehito Hayakawa (National Institutes for Quantum Science and Technology)

Neutirno-process_presolar_grainsI_NuSym25.pdf

NuSym Poster Session: Poster with Supplement

24 Correlations of Q_{\beta}-values and properties of Skyrme functionals

The half-lives of nuclei undergoing $\beta$-decay are highly sensitive to the $Q_{\beta}$ values. In order to achieve reliable theoretical predictions, it is crucial to construct an effective interaction or energy density functional (EDF) capable of systematically reproducing experimental $Q_{\beta}$ values. One of the main challenges is identifying which EDFs can accurately predict $Q_{\beta}$ values. To address this issue, we investigate the bulk nuclear properties that exhibit correlations with $Q_{\beta}$. The central goal of this study is to pinpoint which of these bulk properties most significantly impact $Q_{\beta}$. Our analysis utilizes a wide range of Skyrme energy density functionals under the assumption of spherical symmetry. Specifically, we examine the correlations between $Q_{\beta}$ and various nuclear bulk properties by computing Pearson correlation coefficients across 42 different Skyrme EDF parameter sets. We observe that the symmetry energy at sub-saturation (low) densities correlates strongly with $Q_{\beta}$ values. However, this correlation diminishes as the density increases. Our results indicate that a symmetry energy of 32.8 ± 0.7 MeV and an effective mass 𝑚∗/𝑚≥0.75 at saturation density provide the best agreement with experimental $Q_{\beta}$ values, offering a promising direction for improving $\beta$-decay predictions.

Speakers: Futoshi Minato (Kyushu university), Kenichi Yoshida (The University of Osaka), Yifei Niu (Lanzhou University)

25 Coulomb effects on the symmetry energy and nuclear structure in finite nuclei

We investigate the role of the Coulomb interaction in nuclear deformation and stability across the nuclear chart. Using self-consistent Hartree-Fock-Bogoliubov (HFB) calculations within DFT theory, we systematically evaluate quadrupole deformation for even-even nuclei with proton numbers ranging from Z=2 to Z=118.
By comparing results obtained with and without the Coulomb interaction, we find that the quadrupole deformation tend to be larger due to the Coulomb interaction. In addition, in the absence of the Coulomb interaction, nuclei tend to stabilize near the N=Z line, reflecting the isospin symmetry of the strong interaction. When the Coulomb interaction is included, this symmetry is broken, and additional neutrons are required to overcome the proton-proton repulsion. As a result, the region of stability systematically shifts toward neutron-rich region.
These results illustrate how the Coulomb interaction influences the isospin structure of finite nuclei. In particular, the deformation patterns and stability trends we observe may provide insight into how symmetry energy manifests in realistic nuclear systems through the interplay of nuclear and Coulomb forces.

Speaker: Kenta Hagihara (University of Tsukuba)

26 Deblurring on triple-differential yield from $ {}^{132,108} \mathrm{Sn} + {}^{124,112} \mathrm{Sn} $ @ $ 270 A \, \mathrm{MeV} $ collision from SPiRIT

The triple-differential yield as functions of the transverse momentum, the
rapidity and the azimuthal angle relative to the estimated reaction plane
is a critical observable for the collective-flow analysis in heavy-ion
collisions. However, the triple-differential yield can be degraded by not
only methodology to estimate reaction plane direction but also imperfect
detector performance such as the detection inefficiency and detector
acceptance. Richardson-Lucy deblurring algorithm describes a method
to restore the degraded intensity distributions and is widely used in
various fields such as optics and astronomy. Inspired by this algorithm,
the dedicated deblurring algorithm has been developed and applied to
the analysis for $ {}^{132,108} \mathrm{Sn} + {}^{124,112} \mathrm{Sn} $ at $ 270 A \, \mathrm{MeV} $ by the SPiRIT
Collaboration. In this presentation, we describe the deblurring process
using the Richardson-Lucy algorithm to restore the triple-differential yield
compared to the results without applying the deblurring process.

Speaker: Jeonghyeok Park (Korea Univeristy)

NuSym2025_포스터_박정혁.pdf

27 Dependence of pair collective mass on pairing collective variables using BCS+QRPA calculations

One of the important correlations in atomic nuclei is pairing, where two nucleons form a pair. The pairing correlation can lead to a phase transition into a superfluid state, analogous to the superconducting state observed in electronic systems.
In the superfluid phase, the global U(1) gauge symmetry is spontaneously broken. As a result, a new type of the collective mode emerges: the pair rotational mode (Nambu-Goldstone mode) which corresponds to the motion along the bottom of a wine-bottle-shaped effective potential, in addition to the pair vibrational mode which involves fluctuations in the magnitude of the order parameter.
In finite systems such as nuclei, phase transitions do not occur sharply due to significant quantum fluctuations. Instead, a critical state exists between the normal and the superfluid phase. Nuclei near closed-shell configurations are typically considered to exhibit pair vibrational modes. However, previous studies (Clark et al. 2006) have shown that some magic-number nuclei may actually be in a critical state.
To describe shape coexistence phenomena with quantum fluctuations, such as those observed in $^{98}$Kr, five-dimensional quadrupole collective Hamiltonian has been extensively used (Próchniak and Rohoziński 2009). In a similar spirit, describing nuclei in a pairing critical state requires the construction of a pair collective Hamiltonian that can simultaneously include both pair rotational and vibrational dynamics and their couplings. Despite its importance, research on pair collective Hamiltonians remains limited, with most models relying on simple monopole pairing interactions (Bes et al. 1970). Consequently, current approaches are restricted to narrow model spaces and can only be applied to a limited number of nuclei.

To extend the applicability of the pair collective models to a wider range of nuclides, we aim to construct the pair collective Hamiltonian based on nuclear density functional theory. The potential energy surface is expressed as a function of the pairing gap (the collective variable), while the inertial functions, namely the pair rotational moment of inertia and the pair vibrational mass, is obtained using local QRPA calculations that account for the pairing gap dependence. We then construct a pair collective Hamiltonian that can describe the pair dynamics in the critical regime and allows us to reassess the stability of the magic nuclei from the perspective of the pairing correlations.
As a first step toward this goal, we have obtained the potential energy surface using BCS calculations with constraints on the pairing gap, employing monopole pairing interactions. In this presentation, we will also discuss the pairing gap dependence of the pair rotational moment of inertia and the pair vibrational mass.

Speaker: Chisato Ruike (University of Tsukuba)

28 Disentangling symmetry energy and surface properties of warm nuclear matter for binary neutron star mergers equation of state

The properties of neutron star matter in the low-density regime, where nucleonic clusters coexist with a neutron fluid, remain rather uncertain, but are essential for the accurate modelling of neutron star mergers. We systematically explore how nuclear physics inputs, particularly those related to the symmetry energy and the treatment of finite-size effects, impact the properties of warm, inhomogeneous matter.
We start by comparing zero-temperature models: compressible liquid-drop, extended Thomas-Fermi (ETF), and ETF with shell corrections, highlighting their different treatment of surface tension and quantum effects, and their consequences for crustal composition [1]. Then, we assess how chiral Effective Field Theory and Skyrme interactions diverge in predictions for the neutron star crusts [2], emphasizing the role of pure neutron matter and the symmetry energy. At finite temperatures, we contrast compressible liquid-drop and temperature-dependent ETF approaches, revealing agreements in thermodynamics but discrepancies in cluster composition and neutron skin thickness [3].
We will present new results with different Skyrme parametrizations that demonstrate how variations in the symmetry energy at T > 0 alter the crust-core transition, cluster populations (A, Z), pressure, and sound speed—key ingredients for merger simulations.
We conclude by discussing open questions: Should one prioritize symmetry energy constraints, surface energy descriptions, or both? How do these choices affect gravitational-wave observables and kilonova signals?
Our work provides a benchmark for constructing a unified equation of state at finite temperatures, clarifying where simplified models are sufficient and where microscopic treatments are necessary for multi-messenger astronomy.

[1] G. Grams, J. Margueron, R. Somasundaram, N. Chamel, and, S. Goriely, J Phys: Conf.Seri, 2340, 012030 (2022).
[2] G. Grams, J. Margueron, R. Somasundaram, and S. Reddy, Eur. Phys. J. A 58, 56 (2022).
[3] G. Grams, N.N. Shchechilin, T. Diverres, A.F. Fantina, N. Chamel, F. Gulminelli, Universe, 11, 172 (2025).

Speaker: Guilherme Grams (University of Potsdam)

29 Exploring surface properties of neutron stars using the coherent density fluctuation model

Neutron stars serve as unique astrophysical laboratories for probing the equation of state (EoS) of matter under extreme density and isospin asymmetry [1]. Understanding their surface characteristics, particularly the surface incompressibility and surface symmetry energy, provides vital constraints on nuclear interactions far from saturation conditions. This study utilizes the coherent density fluctuation model (CDFM), originally formulated for finite nuclei [2-5], to explore these surface properties in neutron stars. Within CDFM formalism, the neutron star is treated as a macroscopic analogue of a finite nucleus, enabling the translation of nuclear matter properties, derived from an underlying energy density functional (EDF), from momentum space to the coordinate space description of the star's surface region.
We employ a range of EDFs based on established Skyrme interactions, specifically selecting 16 parameter sets that satisfy constraints derived from symmetric nuclear matter and pure neutron matter properties [6]. The macroscopic structure, including mass-radius profiles, is determined for each EoS by solving the Tolman-Oppenheimer-Volkoff (TOV) equations [1]. Subsequently, the CDFM formalism is applied, using the calculated neutron star density profiles, to compute the surface incompressibility and symmetry energy.
Our analysis focuses on the dependence of these surface quantities on the neutron star's total mass and the specific Skyrme parameterization used, highlighting the sensitivity to the stiffness of the EoS. The results demonstrate the successful application of the CDFM framework across vastly different scales, bridging the physics of finite nuclei and compact stars, and reinforcing its utility in nuclear astrophysics investigations.

References
[1] N. K. Glendenning, Compact stars (Springer 1997).
[2] M. K. Gaidarov et al., Phys. Rev. C 85, 064319 (2012).
[3] M. Bhuyan et al., Phys. Rev. C 97, 024322 (2018).
[4] P. K. Yadav, R. Kumar, and M. Bhuyan, Chin. Phys. C 46, 084101 (2022).
[5] P. K. Yadav, R. Kumar, and M. Bhuyan, Europhysics Letter 146, 14001 (2024).
[6] M. Dutra et al., Phys. Rev. C 85, 035201 (2012).

Speaker: Mr Praveen Kumar Yadav (Thapar Institute of Engineering and Technology)

30 Impact of the nuclear equation of state on the formation of twin stars

By inverting the observational data of several neutron star observables in the three-dimensional parameter space of the constant speed of sound (CSS) model while fixing all hadronic equation-of-state parameters at their currently known most probable values, we constrain the properties of the first-order phase transition from hadronic to quark matter, as well as the speed of sound in quark matter. We further discuss the potential existence of twin neutron stars (two stable star with same mass but different radii) and analyze how nuclear EOS and crust-core transition density impact twin star formation. Our results show that the symmetry energy of neutron-rich nucleonic matter significantly affects twin star formation, particularly through its slope $L$ and curvature $K_{\rm sym}$.

Speaker: Naibo Zhang (Southeast University)

31 Measurement of Proton Elastic Scattering from 136Xe at 200 and 300 MeV/nucleon

Proton elastic scattering is one of the best probes to determine the proton and neutron density distributions in nuclei, which are not only fundamental properties of nuclei but also plays an important role in studying the symmetry energy of the nuclear matter equation of state. We measured the proton elastic scattering from 136Xe at 200 and 300 MeV/nucleon in inverse kinematics with high intensity beam, about 600 kcps. In this presentation, we will report the preliminary results of the experiment.

Speaker: Takayuki YANO (Kyoto University)

32 Neutron Star Cooling with Y+K phase

The hot neutron star cools down due to the loss of neutrinos produced by the scattering of particles mainly inside the core, which enables us to probe the state of high-density matter through temperature observations. Recent X-ray observations have confirmed the existence of too cold isolated neutron stars beyond the standard cooling scenario without rapid cooling (i.e., minimal cooling scenario). This may imply the existence of exotic particles such as mesons, hyperons, and quarks. Among them, hyperons are considered a powerful candidate for the rapid cooling process known as the hyperon direct Urca process, along with another candidate, the nucleon direct Urca process. However, because of the large uncertainties of baryon superfluidity/superconductivity, whether such rapid cooling can work efficiently as a rapid cooling mechanism is controversial. For instance, if proton superconductivity is strong, both of the direct Urca processes are too suppressed to explain the cold neutron-star observations. We utilize the latest equation of state with the phase of mixed hyperons and Kaon condensation (i.e., Y+K phase), and discuss the impact of Y+K phase on cooling curves, focusing on the role of Kaon Urca process and proton superconductivity.

Speaker: Dr Akira Dohi (RIKEN)

33 Nuclear symmetry energy and exotic structures in the deformed relativistic Hartree–Bogoliubov theory in continuum

The nuclear symmetry energy is a fundamental component of the nuclear equation of state (EoS) that significantly influences the properties of neutron-rich nuclei, heavy-ion collisions, and neutron star structure. In this study, we employ the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the PC-PK1 density functional to systematically investigate the effects of symmetry energy across the nuclear chart, including both stable and exotic isotopes.
Our analysis focuses on observables sensitive to symmetry energy, such as neutron skin thickness ($\Delta r_{np}$), two-neutron separation energies, nuclear deformation, and charge radii evolution. We examine correlations among neutron skin thickness, isospin asymmetry, and shell structure. Results for heavy nuclei such as $^{208}$Pb and $^{132}$Sn are compared with available experimental data.
Additionally, we explore neutron halo formation in weakly bound nuclei near the drip lines, identifying deformation and continuum coupling as key mechanisms. Our calculations successfully reproduce odd-even staggering and kink behavior in charge radii near shell closures, providing microscopic insights consistent with experimental observations.
These results clearly demonstrate the high predictive power of the DRHBc framework for isospin-dependent nuclear structure phenomena and will serve as a crucial theoretical foundation for interpreting and understanding related processes in both finite nuclei and nuclear astrophysics.

Speaker: Myeong-Hwan Mun (Kyungpook National University)

34 Probing the Nuclear Symmetry Energy via the Isovector Reorientation Effect in Polarized Deuteron Scattering

Introduction

The density dependence of nuclear symmetry energy is a key issue in nuclear physics and astrophysics, influencing the structure of neutron stars and the dynamics of supernovae.
The isovector reorientation (IVR) effect in polarized deuteron scattering provides a novel and sensitive probe to constrain the symmetry energy, especially at sub-saturation densities.

Objective

To demonstrate the feasibility of measuring the IVR effect using a polarized deuteron beam at the SAMURAI spectrometer (RIKEN).
To develop and validate methods for monitoring tensor polarization ($p_{z'z'}$, $p_{y'y'}$) of the deuteron beam.

Methodology

Beam and Setup:
Polarized deuteron beam (190 MeV/u) produced and monitored with a dedicated polarimeter.
Scattering on heavy targets ($^{124}$Sn, $^{208}$Pb) with detection of breakup protons (PDC) and neutrons (NEBULA).
Simulation:
Event generation with ImQMD transport model.
Detector response simulated using Geant4.
Key Observable:
$R = \frac{N(p_x^p > p_x^n)}{N(p_x^p < p_x^n)}$ quantifies the IVR effect and its sensitivity to the symmetry energy parameter $\gamma$.

Results

The IVR effect is clearly observed in simulations for both longitudinal and transverse tensor polarizations.
The observable $R$ shows strong sensitivity to the stiffness of the symmetry energy, especially in neutron-rich targets.
The proposed method enables precise monitoring of tensor polarization and robust extraction of symmetry energy information.

Conclusion & Impact

The study demonstrates the feasibility of using polarized deuteron scattering to probe the nuclear symmetry energy.
The results provide valuable constraints for nuclear structure and astrophysics, with implications for understanding neutron stars and supernovae.

Speaker: Baiting Tian

35 Proton elastic scattering experiment for 50Ca in inverse kinematics as a step toward symmetry energy studies

The symmetry energy in the equation of state (EoS) of nuclear matter remains one of the key open questions in both nuclear physics and astrophysics, with significant implications for phenomena such as neutron stars and supernova explosions. Our approach focuses on the differences in proton and neutron density distributions among isotopes, which are expected to provide deeper insight into the nuclear matter EoS. It has been well established in the literature that the angular distribution of proton elastic scattering is particularly sensitive to the neutron and proton density distributions. This sensitivity is especially pronounced for magic nuclei such as Ca (Z=20) and Sn (Z=50), where the proton shell is closed.
A measurement of proton elastic scattering for the neutron-rich nucleus 50Ca has been performed in inverse kinematics at the RIKEN RI Beam Factory (RIBF). In this study, a newly developed ∆E-E telescope array, DELTA—consisting of Silicon Strip Detectors (SSD) and GAGG(Ce) calorimeters (GAGG)—was employed to measure the four-momentum of the recoil protons, in addition to the existing ∆E-E telescope system. In this presentation, results of the 50Ca(p,p) elastic scattering experiment obtained using the missing mass method will be reported. As a next step, we aim to extend this study to proton elastic scattering for 52Ca. Developmental studies toward this future experiment will also be discussed.

Speaker: Tomoya Nakada (Kyoto University)

36 Quark-meson coupling model in heavy-ion collisions

The quark-meson coupling (QMC) model incorporates quark degrees of freedom, unlike the quantum hadro-dynamics (QHD) model. Using the mean-field approximation, the QMC model has been applied to nuclear matter, neutron stars, finite nuclei, and related systems. In this work, we investigate heavy-ion collisions by incorporating the QMC model into the Daejeon Boltzmann-Uehling-Ulenbeck (DJBUU) transport model. We present simulation results for Au + Au and Sn + Sn collisions using both QMC- and QHD-based interactions for comparison. For Au + Au collisions, the QMC interaction successfully reproduces the transverse and directed flows, in agreement with the corresponding QHD results and experimental data. Although the QMC model has a larger incompressibility than QHD, it yields a higher baryon density in the compressed stage. This difference strongly influences the in-medium modification of Δ production; by tuning the in-medium modification parameters, we can reproduce pion observables in Sn + Sn collisions with the QMC interaction. Our results confirm the feasibility of implementing QMC interactions in heavy-ion collision simulations. This study paves the way for studying quark degrees of freedom in intermediate-energy heavy-ion collisions.

Speaker: Mr Dae Ik Kim (Pusan National University)

37 Sensitivity of Collective Flow to Effective Mass of nucleon in Intermediate-Energy $ \mathrm{Xe} + \mathrm{Sn} $ Reactions

The nuclear symmetry energy and its density dependence, particularly
above saturation density, remain among the most significant
uncertainties in the nuclear equation of state (EoS). These properties
play a crucial role in both intermediate-energy heavy-ion collisions and
the structure of neutron star matter. Experimental information at supra-
saturation densities, however, is still limited, making such collisions a
powerful probe of the symmetry energy.
In this study, we investigate the $ {}^{129,124} \mathrm{Xe} + {}^{124,112} \mathrm{Sn} $ reactions at $ 100 \, \mathrm{MeV} $ per nucleon, measured in 1998 at GSI by the INDRA–ALADIN
collaboration. Directed and elliptic flow parameters extracted from the
experiment are compared with transport model calculations employing
the Improved Quantum Molecular Dynamics (ImQMD) framework. Two
Skyrme parameterizations SkM* and Sly4, differing in their treatment of
the iso-vector effective mass and neutron–proton effective mass
splitting, were implemented in the simulations.
By confronting experimental flow observables with theoretical
predictions, we assess the sensitivity of collective dynamics to effective
mass at supra-saturation densities. Our findings provide new constraints
on the density dependence of the symmetry energy in the intermediate-
to-high density regime, thereby contributing to a more precise
determination of the nuclear EoS.

Speaker: Seon Ho Nam (Korea University)

NuSym2025_Kobe_SHNam_ImQMD.pdf

38 Spin-orbit force effect for the oscillation frequency during heavy-ion collisions

The dynamical role of the spin-orbit (SO) coupling is a crucial, but not fully understood, aspect in the description of heavy-ion collisions. We investigate this influence using three-dimensional Time-Dependent Hartree-Fock (TDHF) calculations with the SKY3D code. This study simulates heavy-ion collisions ($Z=6-36$, with neutron numbers $N$ from $Z-4$ to $Z+4$) at a center-of-mass kinetic energy of $E_{\rm cm} = A + e Z^2 / 4R$, with the nuclear radius defined as $R = 1.2 A^{1/3}$ fm. We focus on the effect of the SO coupling on the collective oscillation of the dinuclear system formed during the collision. From the oscillation period $T$, we extract the corresponding restoring force coefficient, $k$, defined as $k = 4\pi^2 \mu / T^2$, where $\mu$ is the reduced mass of the system. Our analysis reveals that $k$ is strongly correlated with the total number of nucleons, $A$. For lighter systems (small $A$), the restoring force is stronger when the SO interaction is included. In contrast, for heavier systems (large $A$), the calculation without the SO force produces a stronger restoring force. In particular, a distinct peak in the restoring force coefficient is observed around $A \approx 60$ in simulations performed without the SO interaction. By examining a broad mass range, we aim to identify clear signatures of the SO interaction in the dynamical situation. This work aims to enhance the understanding of both spin-dependent dynamics and nuclear energy density functionals.

Speaker: Rongjun Liu (Shanghai Institute of Applied Physics, Chinese Academy of Sciences)

39 Symmetry energy effect on hot nuclear matter and proto-neutron stars

We examine the effects of symmetry energy on proto-neutron stars (PNSs) using an equation of state
(EOS) described by the relativistic mean-field (RMF) model. The thermal properties of dense matter and the bulk
properties of PNSs are investigated under the assumptions of isothermy, isentropy, and fixed lepton fractions. The
polytropic index is calculated at finite temperature, revealing a negative correlation with the maximum mass of a
PNS that the EOS can support. The properties of PNSs during the heating and cooling stages along their evolution-
ary path are explored under different combinations of lepton fraction and entropy. We investigate the correlation
between symmetry energy slope L and the properties of PNSs. As L increases, the radius of a PNS also increases;
however, this effect diminishes with a growing lepton fraction in the isentropic case. These results indicate that nuc-
lear symmetry energy and its density dependence play crucial roles in determining the properties of PNSs and their
evolutionary stages.

Speaker: Xuhao Wu

NuSym2025-WU.pdf

40 The properties of hadron-quark mixed phase in neutron stars

Neutron stars are considered as the ideal natural laboratories to study the physics of dense matter, where the matter covers a huge range of densities. The baryon number density in the core of the neutron star can reach 5-10 $n_0$ ($n_0 \sim 0.16\ \rm{fm}^{-3}$), so the hadron-quark deconfinement phase transition is likely to occur. Traditionally, the hadron-quark phase transition in neutron stars has been assumed to be first-order. This naturally suggests that during the transition, the system exists in a mixed phase state. In recent years, we have systematically investigated the potential formation of a structured hadron-quark mixed phase within neutron star interiors. In this report, I will present the results of our calculations.

Speaker: Min Ju (中国石油大学（华东）)

Wednesday 10 September

09:00 Morning Coffee

NuSym Scientific Session: Session 9

Convener: Prof. Hermann Wolter (University of Munich (LMU))

41 Status Report of the ASY_EOS II Experiment And Isotopic Transparency in Central Xe+Sn Collisions at 100 MeV/nucleon

Our presentation will be 2 fold.
The first part will be a short status report of the second campaign of the ASY-EOS experiment held at GSI Darmstadt in March 2025, with the measurement of Au+Au collisions between 0.28 and 1 GeV/nucleon. This new experiment aims at constraining the symmetry energy of nuclear matter at larger densities (about 2.5 times saturation density) with higher accuracy as regard to the first campaign (2011) that has triggered a breakthrough in the knowledge of the symmetry energy at supra-saturation density using heavy-ion collisions.
The second part will concern our recent publication presenting a new method to measure the isotopic transparency in central heavy-ion collisions. This method is based on comparing isotopic yield ratios measured at forward and sideward polar angles and on cross-bombarding heavy nuclei with different neutron-to-proton ratios. We used here measurements of central collisions of isotopically separated $^{124,129}$Xe+$^{112,124}$Sn at 100 MeV/nucleon bombarding energy, measured with the 4π multidetector INDRA at GSI. We found a moderate transparency for hydrogen isotopes, and a high transparency exceeding 50% for heavier fragmentation products with atomic number Z ≥ 3. An anomalously large transparency has been found for alpha particles, and possible explanations will be presented.

Speaker: Arnaud Le Fèvre (GSI Darmstadt)

ArnaudLeFevre-NuSYM25.pdf

42 Investigation of the neutron-proton effective mass splitting via heavy ion collisions

In my talk, I will first mention our efforts on the improvements of the transport models after the TMEP, such as the consistency of the initialization, extended Skyrme momentum dependent interaction, a novel Pauli blocking algorithm, and so on. Then, I will discuss the recent effort on understanding the constraints of the neutron-proton effective mass splitting (Δm_np^) via HICs. We find a strong correlation between the slope of the neutron-to-proton yield ratio with respect to the kinetic energy (i.e., Sn/p) and Δm_np^, with correlation coefficients exceeding 0.80. For the 124Sn +124 Sn system, this correlation reaches 0.928. By comparing theoretical predictions with experimental data, we reveal a novel dependence of the neutron-proton effective mass splitting on momentum: at low kinetic energies, the data favor m_n^>m_p^ which is consistent with the nucleon-nucleus scattering analysis, while at high kinetic energies, they favor m_n^<m_p^ which is an extended understanding of effective mass splitting at high kinetic energy region. This finding provides the first direct evidence that the momentum-dependent symmetry potential likely decreases initially and then increases with momentum.

Speaker: Yingxun Zhang (China Institute of Atomic Energy)

Eff-mass-2025-zhyx.pptx

43 Pion potentials and its effect on pion production in heavy-ion collisions

To study the pion production in heavy-ion collisions, we developed the transport model~[1] which combines the nucleon dynamics obtained by the antisymmetrized molecular dynamics (AMD) model with a newly developed transport code which we call sJAM. In the previous work~[1], we treated the collision terms of the $NN \leftrightarrow N \Delta$ and $\Delta \leftrightarrow N \pi$ processes with the rigorous conservation of energy and momentum under the presence of momentum-dependent potentials for the initial and final particles of the process. The potentials affect not only the threshold condition for the process but also the cross section in general as a function of the momenta of the initial particles, which is treated in a natural way. We found that the momentum dependence of the neutron and proton potentials has a significant impact on the $NN \to N \Delta$ process, and this information is strongly reflected in the charged pion ratio ($\pi^-/\pi^+$). However, the pion potentials were not included in the previous work~[1]. In the present work, we include the pion potentials in the AMD+sJAM model to study the effect of the pion potential on the pion production in heavy-ion collisions. We find that the pion potentials not only directly affect the $\Delta\to N\pi$ process and the mean field propagation of pions, but also the $\Delta$ production such as $NN \leftrightarrow N \Delta$ due to the change in the $\Delta$ spectral function and the $\Delta$ decay width. We will discuss how the pion potentials affect the pion observables in the heavy-ion collisions.

[1] N. Ikeno and A. Ono, Phys. Rev. C 108, 044601 (2023).

Speaker: Natsumi Ikeno

Nusym25_ikeno.pdf

10:40 Coffee Break

NuSym Scientific Session: Session 10

Convener: Pawel Danielewicz (Facility for Rare Isotope Beams, Michigan State University)

44 (Anti-)Hypertritons in heavy ion collisions and Y-N interaction

The hypertriton was first discovered in 1952 by Marion Danysz and Jerzy Pniewski [1] using a balloon-flown emulsion plate exposed to high-energy cosmic rays and was later studied through the interaction of stopping negative kaons in a helium bubble chamber [2]. It is now known that the Λ hyperon in a hypertriton has a separation energy of only about 130 keV and a spatial separation of roughly 10 fm from the proton and neutron, making it resemble a nucleus with a Λ halo. More recently, both hypertriton and anti-hypertriton have been observed in relativistic heavy-ion collisions at RHIC [3] and the LHC [4]. Their measured yields can be well described by the coalescence model, which is based on the recombination of Λ hyperons and nucleons at kinetic freeze-out [5]. This offers a promising avenue for probing the Λ-nucleon interaction [6]. This talk will review the status of (anti-)hypertriton studies in heavy ion collisions and discuss their implications for understanding the spin structure of (anti-)hypertriton, Λ-nucleon interaction, and the properties of nuclear stars.

[1] M. Danysz and J. Pniewski, Philos. Mag. 44, 138 (1953).
[2] D. H. Davis, et al., Part. Fields 43, 38 (1991).
[3] STAR Collaboration, Phys. Rev. C 97, 054909 (2018).
[4] ALICE Collaboration, Phys. Lett. B 754, 360 (2016).
[5] K. J. Sun, C. M. Ko, and B. Donigus, Phys. Lett. B 792, 132 (2019).
[6] Y. G. Ma, Nucl. Sci. Tech. 34, 97 (2023).

Speaker: Che-Ming Ko (Texa A&M University)

nusym25_ko.pdf

45 Experimental study of two-body hyperon-nucleon interactions toward understanding dense hyperonic nuclear matter

To study the structure of neutron stars, it is important to consider the hyperons that are expected to appear in the core to suppress the high Fermi energy of neutrons. In particular, since the observation of a neutron star having twice solar mass in 2010, there has been much discussion about how to compensate for the drop in the pressure of the star caused by the appearance of hyperons, and the importance of the three-body force including hyperons has been actively discussed. In this situation, deriving reliable two-body hyperon-nucleon interactions is indispensable for discussing the structure of neutron stars and the three-body force. So far, the hyperon-nucleon interaction has been extracted from the structure of hypernuclei, but it has not yet been accurately determined due to the uncertainty of deriving two-body forces from many-body systems. We aim to establish the hyperon-nucleon interaction from two-body scattering data of hyperons and nucleons, and are promoting hyperon-proton scattering experiments. In the Σ- proton scattering experiment at J-PARC, we have succeeded in measuring the differential cross sections for Σ-p, Σ+p elastic scatterings and Σ-p→Λn inelastic scattering with unprecedented precision in the Σ momentum range of 0.45-0.8 GeV/c. Using our data, the chiral hyperon-nucleon interaction has been extended to NNLO. In order to elucidate the ΛN interaction, which is the most important of the hyperon-nucleon interactions, through scattering experiments, we have currently launched a Λ-proton scattering experiment using photo-produced Λ at SPring-8. In parallel with these scattering experiments, we are also conducting collaborative research to derive the YN interaction from lattice QCD and the ΣN cusp measurement as the comprehensively study of interactions of strangeness −1 sector.
In this talk, I will introduce our research for establishing hyperon-nucleon interactions, focusing on the results so far and the current progress of hyperon-nucleon scattering experiments, and also discuss its relevance to neutron star research.

Speaker: Koji Miwa (Tohoku University)

NuSym_miwa.pdf

12:10 Excursion

See https://indico2.riken.jp/event/5134/page/447-excursion

17:30 Conference Dinner

See https://indico2.riken.jp/event/5134/page/448-conference-dinner

Thursday 11 September

09:00 Morning Coffee

NuSym Scientific Session: Session 11

Convener: Bao-An Li (East Texas A&M University)

46 Role of dense matter and neutrinos in core-collapse supernovae and hot neutron stars

I will overview the influence of hot and dense matter in core-collapse supernovae and neutron stars concerning neutrino emission and nucleosynthesis. Supernovae, starting from the gravitational collapse of massive stars, provide bright displays, compact objects (neutron stars or black holes), supernova neutrinos, and heavy elements. The mechanism of supernova explosions has been a longstanding problem of nuclear astrophysics to determine their outcomes. Various conditions of nuclear asymmetry at extreme conditions appear from the collapse of stars, core bounce, and the birth of compact objects. I will describe the recent progress of astrophysical simulations with nuclear physics and discuss the influence of data tables of the equation of state (thermodynamical quantities and compositions) on supernova dynamics, the final fate of compact objects, and neutrino emissions.

Speaker: Prof. Kohsuke Sumiyoshi (National Institute of Technology, Numazu College)

2025-09a_NuSym.pdf

47 An update to the neutron star mass and radius measurements from NICER data

Since 2017, The Neutron Star Interior Composition Explorer (NICER) on the International Space Station has been in collecting observational data from millisecond pulsars. This old and stable neutron stars are ideal objects to constrain dense nuclear matter. Their hot ($10^6$ K) surface emission, located at the base of the magnetic field, emit X-rays that are seen as X-ray pulsations by the observer as the neutron star rotates. Furthermore, the effects of special and general relativity affect the shape of these X-ray pulsations (light-bending and Doppler are the dominant effects). Therefore by modelling the X-ray pulsations, one can deduce the intensity of the gravitational field, and therefore the compactness of the neutron star. We have been applying this technique to NICER data and obtained measurements from five neutron stars, and a few more analyses are in progress. In this talk, I will summarise all results, emphasising on the most recent ones, their possible caveats, as well as the implications for the equation of state of dense matter. The talk will also include a discussion of expected constraints from future observatories.

Speaker: Sebastien Guillot (IRAP / U. Toulouse)

Guillot - NuSYM 2025.pdf

48 From days to minutes: machine learning transforms multi-messenger study on neutron star

Bayesian frameworks that combine theory, nuclear experiments, and astrophysical observations, such as GW170817 and NICER, have successfully placed strong constraints on the neutron star equation of state (EOS). However, the computational demands, which require days to weeks, have limited progress. Recent breakthroughs in machine learning, differential programming, and GPU acceleration transform this bottleneck. Normalizing flow-enhanced samplers analyze binary neutron star mergers in 20 minutes, while gradient-based methods enable complete Bayesian equation of state (EOS) inference in under one hour without the need for pre-trained emulators. This computational revolution enables previously impractical investigations, including high-dimensional parameter scaling, direct EOS breakdown density determination, and the revelation of nuclear parameter degeneracies. Our framework positions the field to fully exploit current and future data while opening a new window for studying supranuclear matter.

Speaker: Peter Pang (Nikhef / Utrech University)

PTHP_nusym25.pdf

10:40 Coffee Break

NuSym Scientific Session: Session 12

Convener: Jerzy Lukasik (Institute of Nuclear Physics IFJ-PAN)

49 A combined constraint on EOS, at high densities, by connecting neutron star observations and the data from heavy ion reactions

I will present a new way to combine constraints on the high density QCD equation of state, from connecting neutron star observations to data from heavy ion reactions at the HADES experiment. In this new setup, the Chiral Mean Field Model, which can describe neutron star and iso-spin symmetric matter, is used for the consistent calculation of the density and momentum dependent potentials of baryons which are then implemented in the UrQMD transport model. In contrast to previous studies, the same equation of state constrained from neutron star properties is also able to describe experimental observables in heavy ion reactions at the HADES experiment. Unlike many other approaches our results are not constraint to densities up to nuclear saturation or perturbative results which allows a continuous description of the equation of state over a large range in baryon density.

Speaker: Dr Jan Steinheimer-Froschauer (GSI)

NuSYM_25_steinheimer.pdf

50 Constraining the EoS of dense neutron rich matter with pion production and flow

Measurements of nucleus-nucleus collisions at the RIBF facility allows us to place constraints on the density dependence of the symmetry energy and on the pressure from the symmetry energy. When we combine these measurements with existing constraints on the symmetric matter EoS, we have obtained constraints on the Equation of State (EoS) of neutron-rich matter. These constraints are relevant to laboratory experiments and also to neutron star observations. In my talk, I will discuss the present status of these constraints and recent progress towards an improved understanding of the EoS of dense matter.

Speaker: William Lynch (FRIB and Michigan State University)

Nusym25_lynch_new_new_2 Autosaved.pdf

51 Experimental studies on symmetry energy using CSHINE

Symmetry energy, closely tied to the isospin dimension of the equation of state for nuclear matter, connects the fundamental properties of microscopic atomic nuclei and macroscopic neutron stars. In terrestrial laboratories, heavy-ion collisions offer a unique way to investigate the characteristics of symmetry energy. After over a decade of dedicated research, a Compact Spectrometer for Heavy Ion Experiments (CSHINE) has been successfully developed, and multiple experiments have been carried out using this facility.

In this talk, two previous works on isospin chronology [Phys. Lett. B, 825, 136856 (2022)] and isospin "ping-pang" emission [Phys. Rev. C, 107, L041601 (2023)] will be briefly reviewed. A recently completed study on the enhancement of neutron-rich particle emission from the out-of-fission-plane region in 25 MeV/u Kr+Pb reactions will then be discussed in detail [Nuclear Science and Techniques, 36, 155 (2025)].

In this study, the "³He-puzzle" in the energy spectrum was observed even during the fast fission process. Using a data-driven energy-spectrum peak-cutting scheme, it was found that the yield ratio R(t/³He) increases with the angle relative to the fission plane, indicating a significant enhancement of neutron-rich particle emission from the out-of-fission-plane. This phenomenon reveals the isospin distribution in fast fission processes and provides a novel probe for investigating nuclear symmetry energy during fast fission.

Finally, a discussion will be presented on the challenges encountered in our research and the future directions required for both experimental and theoretical investigations.

Speaker: Yijie Wang (Department of Physics, Tsinghua University)

20250911-Yijie Wang-NuSym2025.pdf

12:30 Lunch and Coffee

NuSym Scientific Session: Session 13

Convener: Arnaud Le Fèvre (GSI Darmstadt)

52 The measurement and analysis of neutron-neutron correlation function in the heavy ion experiment

The isospin-dependent equation of state of nuclear matter, i.e. symmetry energy plays an important role in the study of nuclear physics and astrophysics. The calculation of transport model has shown the symmetry energy affects significantly the nucleon emission times in HIC leading to significant variation of two-nucleon correlation functions.

Recent years, a compact spectrometer for heavy ion experiment（CSHINE）has been built, which has the ability to measure light charged particles, and the two charged particle correlation functions have been obtained. In 2024, a neutron array with 212ps time resolution has been mounted on CSHINE[ Nucl. Inst. Meth. A 1070(2025) 170055], and the neutron-neutron correlation function is obtained in 124Sn+124Sn at 25MeV/u. A novel method to subtract the crosstalk effect is used to avoid the distortion on the n-n correlation function. Finally, the scattering length, effective range, source size and timescale are obtained by Lednicky-Lyuboshitz approach. The interaction parameters are consistent with the low energy scattering experiment, demonstrating that femtoscopic correlation function method in heavy ion reactions provides an valid means to study the n-n strong interaction and to further shed light on the charge symmetry breaking of nuclear force[Phys. Rev. Lett. 134, 222301 (2025)].

Speaker: Dawei Si (Tsinghua University)

DaweiSi_nnCorrelationFunction.pdf

53 Nuclear Equation of State constrained by nuclear giant resonances

Nuclear giant resonances provide useful constraints on nuclear equation of state (EoS). For example, the isoscalar giant monopole resonance provides direct constraint on nuclear incompressibility and the isovector modes provide useful information on symmetry energy. In this talk, I will show you the unified description of giant monopole resonance in Sn and Pb isotopes is achieved by using the quasiparticle vibration coupling approach, which solves the puzzle “Why are tins so soft?”.
Besides the giant resonances, the GW170817 neutron star merger event and the PREX-2 experiment for neutron skin measurement have provided new clues in understanding nuclear Equation of State (EoS). However, inconsistency between tidal polarizability from GW170817 event and neutron skin thickness of 208Pb R208 from PREX-2 was found based on relativistic energy density functionals (EDFs). In this talk, I will also show you how the inconsistency is reconciled.

Speaker: Yifei Niu (Lanzhou University)

YifeiNiu2025@NuSym.pdf

YifeiNiu2025@NuSym.pptx

54 Equation of State of Neutron Star Cores

We present a model-independent framework to study neutron star (NS) cores by reformulating the Tolman–Oppenheimer–Volkoff (TOV) equations into a dimensionless form using scaled pressure and energy density. This intrinsic and perturbative analysis (IPAD-TOV) enables direct extraction of core equation-of-state (EOS) information from NS observables such as mass, radius, and compactness, without relying on any specific nuclear EOS model. We demonstrate that the inherent nonlinearity of the TOV equations forbids a linear EOS in the stellar core and leads to universal scaling relations connecting NS observables to their central thermodynamic conditions. Crucially, by combining these relations with the stability condition we reveal why there must exist a maximum mass for stable NSs. Our approach further constrains the EOS at the centers of canonical and massive NSs and sheds light on the properties of the densest visible matter in our Universe.

Speaker: Dr Bao-Jun Cai (Fudan University)

Nusym25-BJCai.pdf

15:10 Coffee Break

NuSym Scientific Session: Session 14

Convener: Byungsik Hong (Korea University)

55 Nuclear pasta in neutron stars: role of the symmetry energy and fully microscopic treatment

The extreme conditions encountered in neutron stars (NS) require the extension of the quantum chromodynamics phase diagram from the temperature-density plane to the isospin dimension. The crucial parameter for the description of nuclear matter in these very neutron-rich environments appears to be the nuclear symmetry energy. The smallest proton fractions (down to ≈ 3 %) can be found deep in the crust of NS. This region is predicted [1,2] to consist of very exotic nuclear configurations resembling spaghetti, lasagna or even bucatini and commonly referred to as “nuclear pasta”. Because of their peculiar structure, these pasta phases alter the transport and mechanical properties of the crust, leaving their imprints on the magneto-thermal evolution, oscillations and the emission of gravitational waves by NSs. The abundance of nuclear pasta in NS is governed to some extent by the symmetry energy at sub-saturation densities [3,4].

Recently [3,4], we have investigated the existence of nuclear pasta within the semiclassical extended Thomas-Fermi (ETF) approach. We have employed a series of Brussel-Montreal parametrizations of generalized Skyrme functionals that covers different behaviors for the symmetry energy and at the same time accurately reproduces (i) experimental masses of thousands of nuclei and (ii) state-of-the-art ab initio predictions for pure neutron and symmetric nuclear matter. For all adopted parametrizations, we observe that pasta shape transitions occur whenever the volume fraction $u$ occupied by nuclear clusters fills some threshold value $u_t$. In particular, spherical clusters turn into pasta at $u_t$ ≈ 0.14. This quasi-universality of pasta transitions coincides with the predictions of Ref. [2] (however, their values obtained within a liquid-drop picture are systematically higher; the difference can be explained by the curvature correction). The symmetry energy $S(n)$ at baryon number density $n$ is then found to control the density dependence of $u(n)$ and therefore determines the density ranges of the various pasta structures: the higher the symmetry energy at relevant densities, the softer u(n), hence the wider the density range for each pasta configuration.

However, accounting for quantum shell and pairing effects perturbatively within the Strutinsky integral method leads to a substantial shrinking of the pasta layer, questioning its very existence [3,5]. To better assess the presence of nuclear pasta in NS, we follow a fully three-dimensional quantum treatment based on the self-consistent nuclear energy-density functional theory. In the talk, I will show that the accurate determination of such exotic nuclear configurations requires large computational domains (encompassing several pasta replicas) and special convergence strategies of the mean-field problem. The stability of pasta shapes will be discussed through full 3D Hartree-Fock plus BCS pairing numerical calculations using our latest generalized Skyrme functional BSkG4 [6].

References:
[1] D.G. Ravenhall, C.J. Pethick, J.R. Wilson, Phys. Rev. Lett. 50, 2066 (1983)
[2] M. Hashimoto , H. Seki , M. Yamada, Progr. of Theor. Phys. 71 (2), p. 320 (1984)
[3] N.N. Shchechilin, N. Chamel, J.M. Pearson, Phys. Rev. C 108 (2), id.025805 (2023)
[4] N.N. Shchechilin, N. Chamel, A.I. Chugunov, Eur. Phys. Journ. A, accepted (2025)
[5] N.N. Shchechilin, N. Chamel, J.M. Pearson, A.I. Chugunov, A.Y. Potekhin, Phys. Rev. C 109 (5), id.055802 (2024)
[6] G. Grams, N.N. Shchechilin, A. Sánchez-Fernández, W. Ryssens, N. Chamel, S. Goriely Eur. Phys. Journ. A 61 (2), id.35 (2025)

Speaker: Nikolai Shchechilin (Universite Libre de Bruxelles)

Shchechilin_NuSym_25_c.pdf

56 Cooling of Neutron Star with a 2SC+<dd> Phase

Neutron stars are high-density stellar objects that remain after a supernova explosion. Their central density exceeds the nuclear density, and various states are thought to appear in their interiors that do not appear in ordinary nuclei, such as superfluid states of neutrons and protons, quark deconfinement and hyperon mixing. These states have a strong influence on the neutrino emission process, which is the main cooling process in neutron stars, and on the thermal history of neutron stars. Comparison of neutron star temperature observations with cooling calculations can constrain the internal state of neutron stars.

We have calculated the cooling of neutron stars by constructing a model in which quark matter in a colour superconducting state in the core. The colour superconducting state may have several pairings depending on the quark colour and flavour degrees of freedom, and we assume that the CFL (Colour Flavour Locked) or 2SC (Two-Flavour Colour Superconducting) phases appear. We also introduced quark-hadron continuity, where the ${}^3P_2$ superfluidity of neutrons in the hadron phase is taken over by unpaired $d$ quarks in the 2SC phase, and included that state (2SC+<$dd$> phase) in the cooling calculations. The results show that the cooling curves of neutron stars with the 2SC+<$dd$> phase are located in a higher temperature range than those with the 2SC phase and are similar to the CFL phase. According to these results, it can be concluded that the 2SC+<$dd$> phase can be realised in low-temperature neutron stars.

Speaker: Prof. Tsuneo NODA (Kurume Institute of Technology)

NODA-NuSym25.pdf

57 Measurement of the incompressibility in nuclei to reveal the equation of state of nuclear matter

The equation of state of nuclear matter plays essential roles not only in the nuclear structure and dynamics but also in the size and mass relation of neutron stars and in the dynamics of making and merging compact stars. Among various EoS parameters, the incompressibility (K) is particularly crucial as it directly reflects the sound velocity in nuclear matter and provides a robust constraint on the EoS with minimal model dependence.

However, determining the incompressibility presents unique challenges. The incompressibility of the nucleus differs from that of the the infinite matter due to finite-size and surface effects. Furthermore, the experimental access of the proton-neutron asymmetry is limited to the stable isotopes. Therefore Therefore, a comprehensive understanding requires the systematic determination of incompressibility across both stable and unstable nuclei.

The incompressibility of the nucleus can be calculated from the energy of isoscalar giant monopole resonance (ISGMR), which can be selectively populated by inelastic scattering of isoscalar probes such as alpha particles and deuterons. The measurements of the stable nuclei have been intensively performed at RCNP, while the measurements of the unstable nuclei have just started using the gaseous active target around the world. An active target CAT-M has been developed in Japan for inverse-kinematics experiments with high-intensity heavy ion beam, which enables us to perform the systematic measurement in a wide region of the nuclear chart.

In this paper, the recent activities on the measurement of the ISGMR in the world will be briefly reviewed and the development and recent activities with the CAT-M will be introduced.

Speaker: Dr Shinsuke Ota (RCNP, Osaka University)

20250911-NuSYM25-Ota-pub.pdf

Friday 12 September

09:00 Morning Coffee

NuSym Scientific Session: Session 15

Convener: Sherry Yennello (Texas A&M University)

58 Lambda and Sigma single-particle potentials in nuclear matter from chiral EFT: Bridging heavy-ion collisions, hypernuclei, and neutron stars

The hyperon single-particle potential in nuclear matter is a key quantity in discussing whether hyperons can appear in neutron stars. We investigate the Lambda and Sigma potentials calculated by using baryon interactions based on chiral effective field theory (chiral EFT). The resulting Lambda potential is sufficiently repulsive to suppress the appearance of hyperons in neutron stars. To examine the consistency of these potentials with experimental data, we perform model calculations to compare the results with both Lambda hypernuclear data and heavy-ion collision data. For the heavy-ion collision simulation, we newly incorporate the Sigma single-particle potential calculated by using the same baryon interactions as for Lambda. In this talk, we discuss the impact of hyperon potentials on experimental observables and explore whether the differences among the models are significant enough to be tested.

Speaker: Asanosuke Jinno (Kyoto University)

AJ_NuSym_v4.pdf

59 Relevance of non-resonant contributions to pion production in heavy-ion reactions close to threshold

A previous study of symmetry energy using pion production in heavy-ion collisions close to threshold is revisited [1,2]. Formerly neglected contributions, amounting to non-resonant pion production [3], have now been included in the dcQMD transport model. Their impact on total charged pion multiplicity and charged pion ratio is investigated in detail. Following the finding of relatively strong in-medium modification of transition matrix elements for elastic nucleon-nucleon scattering reported in Ref. [4], transition matrix elements for inelastic collisions are adjusted using simple scaling factors depending on density and isospin asymmetry. Their strengths and other quantities of interest, such as Δ(1232) in-medium potentials, neutron-proton effective mass difference and density dependence of symmetry energy, are determined from comparison to experimental data for integrated charged pion multiplicity and ratio [5,6]. It is found that no in-medium modifications of NN→NΔ transition matrix elements are required, while the strength of the isoscalar Δ(1232) potential at saturation is less attractive than that of the nucleon. Values for neutron-proton effective mass difference and slope of the symmetry energy at saturation compatible with world averages are deduced [7].

1. M.D. Cozma, Eur. Phys. J. A 57, 309 (2021);
2. J. Estee et al., Phys. Rev. Lett. 126, 162701 (2021);
3. O. Buss et al., Eur. Phys. J. A 29, 189 (2006);
4. M.D. Cozma, Phys. Rev. C 110, 064911 (2024);
5. W. Reisdorf et al., Nucl. Phys. A 848, 366 (2010);
6. G. Jhang et al., Phys. Lett. B 813, 136016 (2021);
7. M.D. Cozma, in preparation.

Speaker: Dan Cozma (IFIN-HH)

cozma_nusym25.pdf

60 Effects of nuclei shapes in a heavy-ion collision at intermediate energy

Collective flows from heavy-ion collisions have signals from the shapes of colliding nuclei. Most of nuclei are not spherical. The complex structures of atomic nuclei give various shapes: spherical, oblate, prolate shapes, and their co-existence. These shapes give different overlapped area of colliding heavy-ions. The emitting particles from the heavy-ion collision contain information of those nuclear matter which is formed at the colliding region. The transverse momenta of free nucleons are generated at this colliding region and they show collective phenomena. The directed flow (v1) depends on nuclear densities, and the elliptic flow (v2) comes from the eccentricity of overlapped shape. We study collective flows from heavy-ion collision with deformed nuclei. We simulate heavy-ion collisions at intermediate energies using Daejeon Boltzmann-Uehling-Uhlenbeck (DJBUU) model, and calculate the collective flows of free nucleons from collisions. Then, we discuss the effects of nuclear deformation, shape co-existence, and vibration in heavy-ion collisions.

Speaker: Kyungil Kim (Institute for Rare Isotope Science, Institute for Basic Science)

NUSYM2025-Kyungil-20250912.pdf

Status of the RAON Facility(NUSYM2025).pdf

10:50 Coffee Break

NuSym Scientific Session: Session 16

Convener: Dr Abdou Chbihi (GANIL)

61 FRIB’s Experimental Roadmap to the Nuclear Equation of State

The equation of state (EoS) of nuclear matter, particularly its symmetry energy component, remains a central question in nuclear physics and astrophysics. While recent astrophysical observations have provided valuable constraints, experimental input from terrestrial laboratories is essential to disentangle model dependencies and explore the high-density regime. The Facility for Rare Isotope Beams (FRIB) offers a unique opportunity to address this challenge by enabling experiments with neutron-rich radioactive beams that were previously inaccessible. This talk will provide an overview of the current status and future outlook for EoS-related research at FRIB. Emphasis will be placed on the upcoming experiment designed to probe the density dependence of the symmetry energy using heavy-ion collisions. It will also highlight long-term plans for the EOS research at FRIB and efforts to upgrade and integrate key detector systems. These developments position FRIB to play a key role in constraining the nuclear EOS over the next decade.

Speaker: Zbigniew Chajecki (Western Michigan University)

NuSYM25_chajecki.pptx

62 Status of FAIR: Towards the determination of the nuclear EOS

The Facility for Antiproton and Ion Research (FAIR) in Darmstadt, Germany is a next-generation accelerator facility designed to explore the properties of strongly interacting matter at extreme conditions of temperature, density, pressure, and isospin. One of its central goals is to constrain the nuclear matter equation of state (EOS) which is key to understanding the QCD phase diagram and astrophysical phenomena like neutron stars and supernovae.
At FAIR, a suite of complementary experiments — CBM, HADES, NUSTAR, and their hypernuclear programs — aim to constrain the EOS across a wide range of densities and temperatures.
The HADES (High Acceptance Di-Electron Spectrometer) and CBM (Compressed Baryonic Matter) experiments are designed to explore the behavior of strongly interacting matter at high baryon densities and moderate temperatures, using high-energy heavy-ion collisions. HADES complements the CBM setup by operating at lower beam energies and/or lighter systems. Both experiments focus on observables that are sensitive to the pressure-density relation of nuclear matter, such as collective flows, particle yields, and fluctuations of conserved charges. A crucial feature of both CBM and HADES is potential to detect dileptons. These leptonic probes carry undistorted information from the hot and dense states of the collision and provide insight into the in-medium properties of vector mesons. Those observables contribute to constrain the temperature and density evolution in the course of the collision.
The NUSTAR (Nuclear Structure, Astrophysics and Reactions) collaborations explore the EOS at all densities with a particular focus on the low-density, cold but highly asymmetric regime by studying exotic, neutron-rich nuclei far from stability. Key observables like two-neutron removal cross sections and dipole polarizability allow deducing the thickness of neutron skins. Neutron skins as well as high precision measurements of nuclear masses help to constrain the symmetry energy of the EOS and its slope, which are key ingredients for understanding the structure of neutron stars and the crust-core transition.
Additionally, FAIR’s hypernuclear program — pursued through CBM/HADES and NUSTAR — explores the role of strangeness in dense matter. Observables from single and double hypernuclei provide empirical constraints on hyperon-nucleon and hyperon-hyperon interactions, which become significant in the high-density interiors of neutron stars. The presence of hyperons tends to soften the EOS, reducing the maximum mass of neutron stars — a feature known as the "hyperon puzzle”. Precision hypernuclear studies help to resolve this puzzle by providing constraints at or below saturation densities. Novel observables like hyperon collective flow might give access to the hyperon-nucleon potential at higher densities.
In summary, the combination of CBM/HADES and NUSTAR at FAIR enables a comprehensive, multi-faceted exploration of the nuclear matter EOS. Each experiment probes a different regime of density, temperature, and isospin, collectively building a coherent picture of how matter behaves under such extreme conditions.

Speaker: Dr Yvonne Leifels (GSI Helmholtzzentrum für Schwerionenforschung)

63 KRAB detector characteristics and performance during the ASY-EOS II experiment at GSI

The only way to study the properties of asymmetric nuclear matter at high densities in the laboratory conditions is to investigate the relativistic heavy ion collisions. A complementary source of information are the astrophysical observations and gravitational waves. The degree of compression and pressures achieved during the heavy ion collision depend on the susceptibility of the nuclear matter to compression, and hence on its equation of state. In particular, the measured angular and energy distributions of neutrons and protons, light isobars and of the π −and π+emitted form the interaction zone depend on the symmetry energy and its gradients at the attained densities. Precision measurements of the azimuthal distributions of neutrons and protons and light isobars with respect to the reaction plane require specific detectors. The setup for the ASY-EOS II experiment, S122, within the R3B infrastructure at GSI allowed for improved resolution flow measurements through the usage of the NeuLAND neutron/proton detector, the KRAB fast multiplicity trigger, reaction plane and centrality detector, of the CHIMERA multidetector at intermediate angles and of two TOFD time of flight walls for flow measurements at very forward angles and for light charged particles heading towards NeuLAND. The presentation will focus on the KRAB detector constructed to fulfill the special requirements for the multiplicity trigger around the target in the ASY-EOS II setup. Its characteristics and performance measured during the tests at CCB on the proton beam and at GSI on the relativistic Au beams as well as some preliminary results obtained during the ASY-EOS II experiment in March 2025 will be presented.

Speaker: Jerzy Lukasik (Institute of Nuclear Physics IFJ PAN)

lukasik_nusym25.pdf

12:40 Lunch and Coffee

NuSym Scientific Session: Session 17

Convener: Betty Tsang (Michigan State University)

64 CEE experiment and its future physics program

Heavy-ion collisions (HICs) serve as a unique experimental tool for investigating the properties of nuclear matter under extreme conditions in the laboratory. At HIRFL-CSR energies, HICs can produce nuclear matter at densities reaching 2–3 times the normal nuclear saturation density. The HIRFL-CSR External-target Experiment (CEE) is a large-acceptance spectrometer specifically designed to explore frontier topics in high-energy nuclear physics, such as the QCD phase structure and the equation of state of nuclear matter.
In this talk, we will present an overview of the current status of the CEE experiment, progresses in simulation and data analysis software as well as its future physics program.

Speaker: Yapeng Zhang (Institute of modern physics, CAS)

NuSym25-Status of CEE-YapengZhang-Kobe.pdf

65 Perspectives of RIBF toward the Determination of the Nuclear Equation of State

The Radioactive Isotope Beam Factory (RIBF) at RIKEN is an accelerator-based experimental facility capable of producing energetic radioactive isotope beams by employing the large-acceptance fragment separator BigRIPS and the superconducting ring cyclotron SRC.
At RIBF, several experimental programs are underway to determine the nuclear equation of state (EoS) through studies of both nuclear structure and nuclear reaction.
So far, these efforts have included: proton elastic scattering measurements for neutron-rich isotopes, systematic measurements of the isoscalar giant monopole resonances across isotope chains, and the determination of nuclear radius from the measurement of reaction cross section.
The nuclear EoS for neutron-rich high-density matter has also been investigated using RI beams as projectiles in heavy-ion collisions — a unique method to create high-density matter in the laboratory.

In this talk, I will present the next-generation experimental programs at RIBF aimed at studying the density dependence of the symmetry energy, along with upgrade plans for RIBF to remain competitive with other next-generation RI-beam facilities.

Speaker: Tadaaki Isobe (RIKEN)

nusym25_isobe_pub.pdf

66 Closing

Speaker: Tadaaki Isobe (RIKEN)

15:10 Coffee Break

Transport Model Evaluation Project (TMEP)

Convener: Akira Ono (Tohoku University)

67 Progress of the box homework on pion production with mometum-dependent mean field

Speaker: Dan Cozma (IFIN-HH)

TMEP_1_Cozma.pdf

68 Comparatative study of realistic heavy-ion collisions including a Bayesian inference using experimental data

Speaker: Prof. Hermann Wolter (University of Munich (LMU))

TMEP_2_Wolter.pdf

69 Thoughts on application of Bayesian model averaging to transport code results

Speaker: Yingxun Zhang (China Institute of Atomic Energy)

TMEP_3_Zhang.pdf

TMEP_3_Zhang.pptx

70 Homework proposal for uncertainty quantification

Speakers: Dan Cozma (IFIN-HH), zhen zhang

TMEP_4_Cozma-Zhang.pdf

71 Remarks on fluctuations (and correlations) in transport models

Speakers: Maria Colonna (Istituto Nazionale di Fisica Nucleare - LNS), Stefano Burrello (Laboratori Nazionali del Sud (INFN))

TMEP_5_Burrello-Colonna.pdf

72 Box calculations within the BUU equation including light clusters

Speaker: Rui Wang (Laboratori Nazionali del Sud (INFN))

TMEP_6_Wang.pdf

Saturday 13 September

Transport Model Evaluation Project (TMEP)

Convener: Akira Ono (Tohoku University)

73 Review and summary of Friday's discussion

Speaker: Akira Ono (Tohoku University)