SAMURAI International Collaboration Workshop 2015

7 Sept 2015, 08:00 → 8 Sept 2015, 18:30 Asia/Tokyo

RIBF hall (RIKEN Nishina Center)

The SAMURAI facility has been operated successfully in several experiments at the RIKEN RIBF since March 2012. The main aim of the workshop is to summarize the status of projects and experimental programs being conducted and to discuss new proposals. We welcome new collaborators and hope this workshop will be a good place to exchange information on the performance of the SAMURAI spectrometer and to shape new proposals into highly competitive proposals for NP-PAC meetings at the RIKEN RIBF. Those who are planning to submit a new proposal with the SAMURAI collaboration in NP-PAC at RIKEN RIBF are strongly encouraged to give a presentation at the workshop. The presentation should include the following experimental information to discuss its feasibility; 1) Motivation and purpose of the experiment, 2) Detector configuration and setting, 3) Trigger condition and expected trigger rate, 4) Status of additional detectors you use, other than the standard SAMURAI detectors. In addition to the submission of the abstract, we kindly ask you submit a pre-proposal describing your new proposal, as an attachment file. The file of the pre-proposal can be found in the middle of this page. The submission of the pre-proposal for this workshop is not mandatory but will be very helpful for improving the feasibility of your experiment as much as possible during the workshop. One can make the pre-proposal submission afterwards but with some deadline in advance of the NP-PAC.

File for preproposal File for preproposal

Monday, 7 September

10:00 → 10:20 Opening address

10:00 Opening remark

Speaker: Prof. Takashi Nakamura (Tokyo Institute of Technology)

10:05 Welcome address

Speaker: Dr Tomohiro Uesaka (RIKEN Nishina Center)

10:20 → 12:10 Progress report - 1

Convener: Dr Tomohiro Uesaka (RIKEN Nishina Center)

10:20 Report on Day one experiments

Report on experimental programs performed in Day one experiments.

Speaker: Dr Yosuke KONDO (Tokyo Institute of Technology)

10:45 Report on Day two experiments

Report on experimental programs performed in Day two experiments.

Speaker: Dr Hideaki Otsu (RIKEN Nishina Center)

11:10 Progress report on missing mass spectroscopy with SAMURAI

Progress report

Speaker: Masaki Sasano (RIKEN Nishina Center)

11:30 Status of the SAMURAI12 experiment preparation

The NP1206-SAMURAI12 experiment aims to provide a quantitative study of the clustering aspects in neutron-rich Beryllium isotopes 10,12,14Be by use of cluster quasi-free reactions in inverse kinematics using a solid proton target. Cluster spectroscopic factors and internal momentum distribution will be extracted from (p,pa) and (p,p6He) quasi-free scattering reactions. Besides this goal, multineutron systems will also be studied using the same setup. The detection system comprises the solid hydrogen target and proton detectors of the ESPRI setup in a modified configuration. Clusters will be detected with SAMURAI and Si-CsI telescopes at larger angles. Residues will be detected by SAMURAI using FDC2 and Hodoscopes. A status of the preparation will be presented.

Speaker: Dr Didier Beaumel (IPN Orsay / RIKEN Nishina center)

11:45 Progress report on polarized target project at SAMURAI:Preparation status for experiment with polarized proton target (SAMURAI13)

Progress report. Spin-orbit interaction in the elastic scattering of 6He on proton will be investicated with a polarized proton target and SAMURAI spectrometer. Spin-orbit coupling can show different behaviour in unstable nuclei due to the diffuse surface structure of nuclei far from the stability. We will present preparation status for the SAMURAI13 experiment including the development of polarized target, a recoil proton detector (ESPRI-RPS) and method to fill the SAMURAI gap chamber with helium gas.

Speaker: Dr Satoshi Sakaguchi (Dept. of Physics, Kyushu University)

12:10 → 14:00 Lunch

14:00 → 15:15 Progress report - 2

Convener: Dr Hideaki Otsu (RIKEN Nishina Center)

14:00 Progress report on SAMURAI TPC

Progress report.

Speaker: Dr Tetsuya MURAKAMI (Department of Physics, Kyoto University)

14:25 Progress report on CATANA

Progress report.

Speaker: Dr Yasuhiro Togano (Tokyo Institute of Technology)

14:50 Progress report on heavy-ion (HI) proton project

Progress report.

Speaker: Dr Valerii Panin (RIKEN, Spin-isospin laboratory)

15:15 → 15:30 Coffee break

15:30 → 16:35 Progress report - 3

Convener: Dr Ken-ichiro YONEDA (RIKEN Nishina Center)

15:30 Progress report on NeuLAND

Progress report.

Speakers: Dr Haik Simon, Prof. Thomas Aumann (Technische Universitaet Darmstadt)

15:55 Progress report on NEBULA+

Speaker: Nigel Orr (LPC-Caen)

16:10 Progress report on MINOS SEASTAR campaign at SAMURAI

Progress report.

Speaker: Dr Pieter Doornenbal (RIKEN)

16:35 → 16:45 Coffee break

16:45 → 18:00 New proposals - 1

Convener: Prof. Thomas Aumann (Technische Universitaet Darmstadt)

16:45 Structure in the Region of N=16: Follow up Studies to NP1106-SAMURAI04

Experiment NP1106-SAMURAI04 “Structure of 18,19B and 21,22C” was run in May 2012 as part of the SAMURAI DayOne campaign of experiments. As will be discussed briefly in the first part of this contribution, whilst the analysis is still underway, the data acquired have enabled a number of interesting results to be obtained for unbound states in the region of the N=16 sub-shell closure below doubly-magic 24O. In the case of the search for the first 2+ state of 22C we have tantalizing evidence for a level around 2.5 MeV above the two-neutron threshold following single-proton removal from 23N. Our investigations of the N isotopes have allowed us to extend the known systems out to unbound 24N, whereby two-proton removal from 26F has been found to populate a single low-lying resonance-like structure. Plans for a more definitive investigation of the 22C continuum states using the MINOS active target coupled with the NeuLAND+NEBULA setup and an improved 48Ca primary beam intensity will be discussed. In addition the prospects for undertaking a search for 23C and 25N will be presented.

Speaker: Nigel Orr (LPC-Caen)

17:10 A Proposal for Invariant Mass Measurement of 39Mg at SAMURAI

We would like to propose an invariant mass measurement of the neutron unbound N=27 nucleus 39Mg, lying one neutron hole outside of the quenched N=28 shell gap. This region of the nuclear chart is an area of significant recent interest, with the quenching of the N=28 shell gap below 48Ca resulting in well-developed ground-state deformation, rapid shape evolution and shape coexistence along the N=28 isotones, and evidence for an extended region of deformation in the Mg isotopes extending from N=20 to N=28. First structural information in the neutron-unbound nucleus 39Mg will provide insight into the evolution of structure both in the neighbouring N=28 isotones, and the Z=12 isotopes. This unbound nucleus will be produced following a one proton removal reaction from a secondary radioactive beam of 40Al on the thick liquid hydrogen target of MINOS. Charged particle decay products will be analyzed through the SAMURAI magnet while neutrons will be detected by the combination of NEBULA and NeuLAND. Details of the proposed experiment and preliminary simulation results will be presented.

Speaker: Dr Heather Crawford (Lawrence Berkeley National Laboratory)

17:35 Study on the cluster structure related to neutron-rich Carbon isotope beams

Nucleon clustering inside a nucleus is an intriguing phenomenon observed since the early time of nuclear physics. For stable nuclei, the cluster structure is generally developed at excited states close to the corresponding particle decay threshold as illustrated in the Ikeda diagram. When approaching the neutron drip line, a large number of cluster configurations are expected both in the excited and ground states. Many theoretical and experimental efforts have been devoted to this topic, but the detailed mechanism of cluster formation in nuclei is still an open question, which is of fundamental importance not only for nuclear physics but also for astrophysics. We propose to study the cluster structure of neutron-rich carbon isotopes with Quasi-Free Scattering (QFS) method at RIBF. High-intensity secondary beams of carbon isotopes can be provided by BigRIPS. To reduce complex target effect from heavier targets, a solid hydrogen target will be used in this research, which will also increase the reaction luminosity. The proposed study will be a kinematically complete measurement, with the outgoing particles detected by high-performance SAMURAI spectrometer, Recoil Protons Spectrometer (ESPRI-RPS) detector, NEBULA array, and silicon-CsI(Tl) telescope. The cluster spectroscopic factors of the carbon isotope chain can then be extracted by employing DWIA calculations, and this will further allow to systematically investigate the behavior of clustering when approaching the drip line. We will also study he cluster structure in the excited states of neutron-rich beryllium isotopes and the neutron-neutron correlation in the multi-neutron clusters, as they will be produced after the QFS alpha knockout from carbon isotopes.

Speaker: Dr Zaihong Yang (RIKEN)

Tuesday, 8 September

10:00 → 10:50 New proposal - 2

Convener: Nigel Orr (LPC-Caen)

10:00 Electric Dipole Response and multi-­neutron decay of n­‐rich weakly bound nuclei

We propose to study the dipole response of weakly bound neutron-rich nuclei close to the drip line via a measurement of the multi-neutron decay after heavy-ion induced electromagnetic excitation. The experiment will make use of the combination of NEBULA plus NeuLAND at SAMURAI, which allows the efficient detection of multi-neutron events. The physics cases selected are 8He, 24O, and 29F. The most important channels for the selected cases are 4n emission in case of 8He, 1n-4n emission in case of 24O, and 2n emission in the case of the Borromean nucleus 29F. In the latter case, the high 2n efficiency is particular important due to the relatively low beam rate of around 40 pps for 29F. All these measurements will be possible for the first time due to the combination of NEBULA and NeuLAND. Almost nothing is known for the dipole response of 8He due to the difficulty of 4n detection. The low energy part (2n channel to 6He) has been measured previously at GSI with insufficient statistics, while the α+4n channel could not be investigated at all. 8He is on the other hand an extremely interesting case since ab-initio calculations of the dipole response are possible (and will be available by end of the year). A previous GSI measurement of the Oxygen chain did not reach 24O due to too less intensity. For 23O, only the 1n channel could be measured. A completion of the oxygen chain would be very valuable due to the new development of RG ab-initio calculations extending the Lorentz-transform method to this region. These ab-initio calculations have reproduced the low-energy Pygmy peak observed in 22O in the previous GSI experiment. Finally, 29F is the heaviest neutron-rich Borromean nucleus reachable today. The dipole response of this nucleus, which will be reconstructed from the 27F+2n decay, will clarify the valence-neutron structure, its main configurations and extension. The experiment could be performed with the standard SAMURAI setup in neutron-configuration using NEBULA plus NeuLAND. For 8He and 24O, high-statistics high-quality data could be extracted for the B(E1) distribution challenging ab-initio theory. For 29F, the measurement would concentrate on the low-energy part (2n decay).

Speaker: Prof. Thomas Aumann (Technische Universitaet Darmstadt)

10:25 Study of cluster degree of freedom in neutron-rich sd-shell nuclei via inelastic alpha scattering (tentative title)

Cluster degree of freedom of neutron rich nuclei with heavier cluster core like O isotope gets much attention. We propose studies of cluster degree of freedom in neutron-rich 28Ne and 32Mg via inelastic scattering on liquid He target, which is useful to excite cluster energy level. Invariant mass spectroscopy of 24O + (28Ne), 24O + 2 and 28Ne+ (32Mg) decay channels is performed in order to reconstruct cluster energy levels which appear above emission threshold (S). This method was successfully utilized with SAMURAI for cluster degree of freedom in 16C (NP1112-SAMURAI08). The setup of the experiment is nearly the same as NP1112-SAMURAI08, except that PDCs are placed to obtain A=Z = 2 particles with sufficient angular covorage as well as appropriately high efficiency for Z = 2 particles. Other decay channels of symmetric break-up as the 32Mg -> xC + xC + xn reactions are expected to be measured simultaneously by the property of large acceptance of SAMURAI.

Speaker: Mr Shunpei KOYAMA (Department of Physics, University of Tokyo)

10:50 → 11:10 Coffee break

11:10 → 12:00 New proposal - 3

Convener: Dr Walter Henning (Argonne National Laboratory (ANL) and Riken Nishina Center (RNC))

11:10 Probing the origin of the Isospin Dependence of Nucleon Correlations and Asymmetry of Parallel Momentum Distribution using (p, pN) reaction at intermediate energy

Single-nucleon knockout reactions of fast radioactive beams have been shown to be a powerful tool for identifying single-particle structure in exotic nuclei and forinvestigating effects of correlations in the nuclear wave functions. The knockout crosssections can be used to infer spectroscopic factors based on the associated reaction models. For the deeply-bound nucleon removal on C/Be target, a strong reduction in the spectroscopic factor deduced using Glauber-based reaction model from experiment relative to the shell-model calculations is found [1]. Such large disagreement has not been explained and is inconsistent with results from systematic studies of transfer reactions [2]. The recently developed INC model has provided a new reaction mechanism resulting in such large disagreement [3], however, our experiment performed at RCNP does not support the INC explanation [4]. Such long-standing puzzle of large disagreement still remains. In addition, the origin of the observed asymmetric parallel momentum distribution (P//) of the residual nuclei, with shape characterized by a steep fall-off on the high momentum side and a long-ranged tail on the low momentum side, is still not understood Instead of C/Be, using hydrogen target structureless probe) for one-nucleon removal leads to a simpler reaction mechanism which can be more accurately described by the three-body breakup reaction dynamics. A recent theoretical work with (p,pN) reaction model provides the first quantitative explanation on the origin of the asymmetric parallel momentum distribution [5]. This model [5], if proved as successful, could resolve the long-standing puzzle of the large disagreement and the origin of asymmetric P// mentioned above, and consequently could serve as a reliable theoretical framework to extract structure information.We therefore propose to perform the cross section and P// measurements of 14O(p,2p)13N reaction at 100 MeV/nucleon in inverse kinematics. Data will be used to assess the reaction model quantitatively. We assume the beam intensity of 14O of 1x105 pps (from LISE++), the cross section to 13N (g.s.) of 10 mb, solid hydrogentarget of 2 mm and other detection efficiency. So to achieve enough statistics for detailed study of P//, 1-day beam time (including 8 hr beam time for empty target measurement) is required. The proposed measurement is considered as a campaign experiment with an approved SAMURAI experiment (NP1206-SAMURAI12: Cluster structure of Beryllium isotopes and study of multineutron systems, spokesperson: Didier Beaumel). Same experimental setup and same primary beam will be used. Tuning the secondary beam from 10,12,14Be to 14O is needed in between two experiments. [1] A. Gade et al., Phys. Rev. C77, 044306 (2008) and reference therein. [2] J. Lee et al., Phys. Rev. Lett. 104, 112701 (2010). [3] C. Louchart et al., Phys. Rev. C 83, 011601 (R) (2011). [4] Y. Sun, J.Lee et al., paper in preparation [5] K. Ogata et al., arXiv:1505.06624 (2015)

Speaker: Dr Jenny Lee (Hong Kong University)

11:35 Fission fragment measurement of U isotope via (p,2p) reaction

The fission threshold energy will be determined for Uranium isotopes with mass numbers ranging from 200 to 230 through the missing mass spectroscopy for the (p,2p) reaction in combination with the fission fragment detection with the SAMURAI spectrometer. These nuclei are of special interest, showing transitions from the asymmetric to symmetric fission and possibly strong effect of the deformation on the shell structures. The measurements will provide a rich source of information of the fission with respect to: 1) fission threshold energy 2) Shell effect of deformation near fission threshold 3) Washout of shell effect at high excitation energy 4) Potential surface energy (scission point, ridge between mass symmetric and asymmetric fission)

Speaker: Mr Masami Sako (Riken Nishina Center)

12:00 → 13:30 Lunch

13:30 → 15:00 Discussion

Convener: Prof. Takashi Nakamura (Tokyo Institute of Technology)

15:30 → 18:30 Excursion?