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SUMMARY:Constraints on the Symmetry Energy from Neutron-Removal Cross Sect
ions
DTSTART;VALUE=DATE-TIME:20180605T011200Z
DTEND;VALUE=DATE-TIME:20180605T013000Z
DTSTAMP;VALUE=DATE-TIME:20200705T101759Z
UID:indico-contribution-11029@indico2.riken.jp
DESCRIPTION:Speakers: Thomas Aumann (Technische Universität Darmstadt\, G
ermany\, GSI Helmholtzzentrum für Schwerionenforschung\, Darmstadt\, Germ
any)\nAn experimentally constrained equation-of-state (EoS) of neutron-ric
h matter is one of the fundamental goals in nuclear physics that has not b
een reached yet.The asymmetry term of the EoS is usually expressed by the
symmetry energy\, with its parameters representing its value $J$ and slope
$L$ at saturation density. To date\, in particular the parameter $L$ is s
till poorly known. One method to bring insight into this open issue is to
relate nuclear observables as theoretically predicted using well-calibrate
d energy-density functionals (EDF) with the corresponding $L$-value. The c
hallenge is to find observables that are sensitive to $L$ and experimental
ly accessible. Two appropriate candidates\, \\textit{i.e.}\, the neutron-s
kin thickness $\\Delta r_{np}$ and the ground-state dipole polarizabillity
$\\alpha_D$ have been identified in recent years. The accurate experiment
al determination of these observables\, however\, remains as a challenging
task in particular for neutron-rich nuclei.\n\nSeveral publications by Ro
ca-Maza \\textit{et al.} demonstrate the feasibility of this method on the
basis of a large set of EDF. The reachable constraint on $L$ naturally sc
ales with the experimental uncertainty of the measured observable while th
e model-dependence\, \\textit{i.e.}\, the scatter of theory points sets a
hard limit that is in the order of $\\pm 10\\\,$ MeV [1]. The latest analy
sis [2] limits the symmetry-energy slope parameter to 20-66 MeV by compari
ng available data for $\\alpha_D$ with calculations in the random-phase ap
proximation.\n\nFollowing the idea described above we have recently propos
ed a new method to constrain $L$ that might allow to reach the theoretical
limit\, namely\, the measurement of neutron-removal cross sections $\\sig
ma_{\\Delta N}$ of neutron-rich nuclei [3]. In our fist systematical study
we show the sensitivity of $\\sigma_{\\Delta N}$ to $\\Delta r_{np}$ and
$L$ for the Sn isotopic chain using a parameter-free eikonal reaction-theo
ry and modified versions of the DD2 interaction where $L$ is systematicall
y varied. We conclude that $L$ can be potentially constrained down to $\\p
m$ 10 MeV\, given that both the measured and calculated cross-section are
known to a 2\\\,\\% accuracy. \nBeing aware that this seems to be an ambit
ious goal\, both aspects\, \\textit{i.e.}\, the status and perspectives of
the reaction theory as well as the requirements of the experiments propos
ed to be performed at R$^{3}$B will be discussed to show that this goal is
definitely not out of reach.\n\nReferences:\n\n[1] X. Roca-Maza\, M. Cent
elles\, X. Vi{\\~n}as\, and M. Warda\, Phys. Rev. Lett. \\textbf{106}\, 25
2501 (2011)\n\n[2] X. Roca-Maza\, X. {Vi{\\~n}as}\, M. Centelles\, B.K. A
grawal\, G. Col{\\`o}\, N. {Paar}\, J. {Piekarewicz}\, and D. Vretenar\, P
hys. Rev. C \\textbf{92}\, 064304\, (2015)\n\n[3] T. Aumann\, C.A. Bertula
ni\, F. Schindler\, and S. Typel\, Phys. Rev. Lett. \\textbf{119}\, 262501
(2017)\n\nhttps://indico2.riken.jp/event/2536/contributions/11029/
LOCATION:Matsue Kunibiki Messe
URL:https://indico2.riken.jp/event/2536/contributions/11029/
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