Rapidity distributions of Z = 1 isotopes and the nuclear symmetry energy from Sn+Sn collisions with radioactive beams at 270 MeV/nucleon

M Kaneko,Y Shimizu,J.W Lee,T Aumann,J Brzychczyk,N Nakatsuka,Y Leifels,P Pawłowski,S Tangwancharoen,J Barney,C Santamaria,H Otsu,T Isobe,H Baba,L Atar,P Lasko,N Chiga,J Estee,M Kurata-Nishimura,M.B Tsang,N Inabe,H Scheit,P Morfouace,H Simon,H.S Lee,S Nishimura,T Ichihara,K Ieki,A Horvat,Y Zhang,R Shane,H Törnqvist,G Cerizza,B Hong,Y Kondo,K Pelczar,J Manfredi,K Boretzky,D Rossi,R Wang,Y Togano,D Suzuki,J Łukasik,J Yurkon,G Jhang,N Fukuda,Y.J Kim,T Sumikama,T Murakami,Hiroshi Suzuki ,Akira Ono ,D S Ahn ,H Sakuraï ,A B Mcintosh ,Hiroyuki Takeda ,Takashi Nakamura ,Xiao Zhang ,W G Lynch ,Richard W Olsen ,Natsumi Ikeno ,Toshio Kobayashi ,S J Yennello ,I Gašparić ,Hiromi Sato ,C Y Tsang

doi:10.1016/j.physletb.2021.136681

Abstract

The rapidity distributions of hydrogen isotopes emitted from central collisions of neutron-rich 132Sn+124Sn and neutron-deficient 108Sn+112Sn systems at 270 MeV/nucleon were investigated at RIKEN-RIBF. The data are compared with antisymmetrized molecular dynamics (AMD) calculations and the rapidity distributions can be reproduced after adjusting the in-medium nucleon-nucleon cross sections. The double ratios between the two reaction systems taken for the relative yields of deuteron to proton (d/p) and triton to proton (t/p) are further examined in the midrapidity domain, where the adjustments in the AMD calculations do not affect much on them. The d/p and t/p double ratios at midrapidity agree well with the ratio of the system neutron numbers and its squared value, respectively, and the rapidity dependence of these double ratios is consistent with a picture of partial mixing of colliding nuclei. By comparing with the AMD model which shows a strong symmetry energy dependence of the t/p double ratio, the experimental result in the midrapidity domain favors the calculation with a symmetry-energy slope parameter around L=46 MeV rather than L=108 MeV.

Highlights

The density dependence of the symmetry energy term in the nuclear equation of state (EOS) is critically important for elucidating the properties of nuclear systems with large neutron-proton asymmetries [1,2,3]
We present the rapidity distributions and spectral ratios of hydrogen isotopes emitted from central collisions of neutron-rich 132Sn+124Sn (N/ Z = 1.56) and neutron-deficient 108Sn+112Sn (N/ Z = 1.2) systems at 270 MeV/nucleon, aiming to comprehend the cluster production and its relevance to the symmetry energy determination
The abscissa takes a scaled rapidity y0 = y/ ycN.mN . − 1, where y is the rapidity of the detected particle in the laboratory frame and ycN.mN . is the rapidity of the nucleon-nucleon (N N) center of mass in the laboratory frame, i.e., Fig. 2. dN/dy0 spectra of (a) protons, (b) deuterons and (c) tritons for 132Sn+124Sn of b0 < 0.15 central collisions, and those for 108Sn+112Sn (d)–(f)

Summary

Introduction

The density dependence of the symmetry energy term in the nuclear equation of state (EOS) is critically important for elucidating the properties of nuclear systems with large neutron-proton asymmetries [1,2,3]. We present the rapidity distributions and spectral ratios of hydrogen isotopes emitted from central collisions of neutron-rich 132Sn+124Sn (N/ Z = 1.56) and neutron-deficient 108Sn+112Sn (N/ Z = 1.2) systems at 270 MeV/nucleon, aiming to comprehend the cluster production and its relevance to the symmetry energy determination These are the first systematic measurements of hydrogen isotopes from HICs using “radioactive isotope beams” in the intermediate-energy domain focusing on the isospin degrees of freedom in HICs. In addition, the use of two reactions with the same total charge of the system allows us to efficiently extract the symmetry-energy effect by constructing the ratio observables, which is expected to reduce the contributions of the Coulomb force. This allows us to directly compare the calculated results and the experimental data to obtain information on the density dependence of the symmetry energy

Experiment

Results and discussion

Summary and perspective