Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 47 (2014)

RIKEN Accel. Prog. Rep. 00 (0)Study of symmetry energy using isospin diﬀusion process inheavy-ion collision at RIBF
N. Nakatsuka,∗1 R.H. Showalter,∗2 T. Isobe,∗3 J. Winkelbauer,∗2 T. Murakami,∗1 W.G. Lynch,∗2 B. Tsang,∗2H. Sakurai,∗3 J. Lee,∗3 M. Nishimura,∗3 S. Nishimura,∗3 Y. Nakai,∗3 N. Fukuda,∗3 N. Inabe,∗3 D. Kameda,∗3T. Kubo,∗3 H. Suzuki,∗3 H. Takeda,∗3 Y. Yanagisawa,∗3 S. Yennello,∗4 A.B. McIntosh,∗4 L. Heilborn,∗4A. Zarrella,∗4 W. Powell,∗5 J. Sampson,∗5 J. Estee,∗2 L. Fei,∗6 G. Zhang,∗6 A. Chbihi,∗7 A. Galindo-Uribarri,∗8E.P. Rodal,∗9 B. Hong,∗10 G. Jhang,∗10 W. Reviol,∗11 D.G. Sarantites,∗11 and L.G. Sobotka∗11The nuclear equation of state (EoS) is an important
information that helps in understanding the astrophysical phenomena such as neutron stars and type-2 supernovae. The EoS shows highest uncertainty on a symmetry energy term, which is proportional to the squareof the isospin asymmetry. We strive to improve theremaining uncertainties of constraints on the density
dependence of the symmetry energy at subsaturation
densities, ρ/ρ0 ≈ 0.4-1 in the so called isospin-diﬀusion
process of heavy-ion collisions. The isospin diﬀusion
process has been observed in the experiments performed at NSCL/MSU using stable nuclear beams1) .
We performed the experiment to measure the isotopic
distribution of the projectile residues from the colli112
sion of cocktail beams, where the 107
49 In and the 50 Sn
124112
beams are on 50 Sn and 50 Sn targets at 70MeV/urespectively. The particle identiﬁcation of projectile
residues is performed by the Bρ-∆E-TOF techniqueusing the ZeroDegree spectrometer. The WashingtonUniversity Microball2) was used to obtain the centrality information. We used Bρ settings of 2.41 and 2.52
T·m in order to avoid beam particles with any charge
states hitting the detectors at F11. The standard beam
tracking and timing detectors at F10 and F11 wereused for reconstructing the beam tracks through thespectrometer. Fig#1 shows a preliminary PID plotof Z versus A = Q for the 107 In on 124 Sn reaction.
Isotopes with Z=30-40 are clearly shown separated in
the ﬁgure. Fig#2 shows a preliminary plot of Z versus
multiplicity of the charged particles obtained by theMicroball. From the obvious correlation between themultiplicity and the size of the residue, we can determine the collision centrality with the help of a model
calculation. In the oﬄine analysis, we will select thedata in the ZeroDegree Spectrometer only from theperipheral events using obtained information from theMicroball. Then the measured yields of isotopes withZ = 30 ∼ 40 will be compared with the theoretical predictions to extract a new constraint on the symmetryenergy at sub saturation densities.

Fig. 1. PID of heavy-ion collision residue performed using
ZeroDegree Spectrometer∗1Department of Physics, Kyoto University
National Superconducting Cyclotron Laboratory, Michigan
State University∗3 RIKEN Nishina Center∗4 Cyclotron Institute, Texas A&M University∗5 Department of Physics, University of Liverpool∗6 Chinese Academy of Sciences∗7 Physics Division, GANIL∗8 Physics Division, Oak Ridge National Laboratory∗9 Institute of Nuclear Sciences, National Autonomous University of Mexico∗10 Department of Physics, Korea University∗11 Department of Chemistry, Washington University∗2Fig. 2. Correlation between multiplicity and Z of residue
using Microball

References
1) M.B. Tsang et al., Phys. Rev. Lett. 92 (2004) 062701.
2) D.G.Sarantities et al., Nucl. Instrum. Methods
Phys.Res., Sec. A 381 (1996) 418.

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