Ⅰ. HIGHLIGHTS OF THE YEAR
RIKEN
Accel. Prog. Rep. 56 (2023)

RIKEN Accel. Prog. Rep. 56 (2023)

Isoscaling in central Sn + Sn collisions at 270 MeV/nucleon††

Condensed from the article in Eur. Phys. J. A 58, 201 (2022)
Department of Physics, Korea University∗2 Facility for Rare Isotope Beams, Michigan State University∗3 Department of Physics, Michigan State University∗4 RIKEN Nishina Center∗5 Department of Physics, Kyoto University∗6 Department of Physics, Tohoku University∗7 Instituto de Fı́sica, Universidade Federal do Rio de Janeiro∗8 Departamento de Engenharia Nuclear, Universidade Federal
de Minas Gerais∗9 Institut für Kernphysik, Technische Universität Darmstadt∗10 GSI Helmholtzzentrum für Schwerionenforschung GmbH∗11 Faculty of Physics, Jagiellonian University∗12 Division of Experimental Physics, Rudjer Boskovic Institute∗13 Department of Physics, Rikkyo University∗14 Department of Life and Environmental Agricultural Sciences,Tottori University∗15 Rare Isotope Science Project, Institute for Basic Science∗16 Department of Physics, Tokyo Institute of Technology∗17 Institute of Nuclear Physics PAN∗18 Cyclotron Institute, Texas A&M University∗19 Nikhef National Institute for Subatomic Physics∗20 Department of Physics, Tsinghua University∗21 Department of Chemistry, Texas A&M University∗1y = 0 - 0.40Z =1

α = 0.29

R 21

Experimental study on the early stage of heavy-ion
collision is challenging as excited fragments produced
from the collision decay into lighter particles before they
are detected. The nuclear isoscaling phenomenon is a
useful tool as the ratio of yields from two different reactions is weakly affected by the fragment de-excitation
process.1)
Rare isotope Tin beams 132 Sn and 108 Sn were produced from RIBF and impinged onto the isotopically enriched Tin targets. Hydrogen and helium isotopes weredetected in SπRIT time projection chamber2) placed inside the SAMRURAI dipole magnet.3) Particles wereidentified from the magnetic rigidity and mean energyloss.4) Most central events with impact parameter b <1.5 fm and mid rapidity range y0 = 0–0.4 are chosen forthis analysis.
The yield ratios between two systems R21 = Y(132 Sn+ 124 Sn)/Y(108 Sn + 112 Sn) as a function of pT /A are
shown in Fig. 1. Given that the collision systems arethermally equilibrated, R21 follow the isoscaling law
R21 = C exp(αN + βZ) where α and β are the fit parameters. Empirically, α and β have similar values withopposite signs, therefore, particles with the same (N −Z)
value show similar R21 values. Figure 1 show isoscaling
effect for pT < 280 MeV/c (left side of vertical dashedline). In this region, the isoscaling fit gives α = 0.29 andR 21J. W. Lee,∗1 M. B. Tsang,∗2,∗3 C. Y. Tsang,∗2,∗3 R. Wang,∗2 J. Barney,∗2,∗3 J. Estee,∗2,∗3 T. Isobe,∗4M. Kaneko,∗4,∗5 M. Kurata-Nishimura,∗4 W. G. Lynch,∗2,∗3 T. Murakami,∗4,∗5 A. Ono,∗6 S. R. Souza,∗7,∗8D. S. Ahn,∗4 L. Atar,∗9,∗10 T. Aumann,∗9,∗10 H. Baba,∗4 K. Boretzky,∗10 J. Brzychczyk,∗11 G. Cerizza,∗2N. Chiga,∗4 N. Fukuda,∗4 I. Gasparic,∗12,∗4,∗9 B. Hong,∗1 A. Horvat,∗9,∗10 K. Ieki,∗13 N. Ikeno,∗14 N. Inabe,∗4G. Jhang,∗2 Y. J. Kim,∗15 T. Kobayashi,∗6,∗4 Y. Kondo,∗16,∗4 P. Lasko,∗17 H. S. Lee,∗15 Y. Leifels,∗10 J. L ukasik,∗17∗2,∗3∗18∗2∗16,∗4∗4,∗5J. Manfredi,A. B. McIntosh,
P. Morfouace, T. Nakamura,
N. Nakatsuka,
S. Nishimura,∗4∗4∗17∗11∗9∗4∗2
H. Otsu, P. Pawlowski,
K. Pelczar,
D. Rossi, H. Sakurai, C. Santamaria, H. Sato,∗4 H. Scheit,∗9∗2∗4∗10
R. Shane, Y. Shimizu, H. Simon,
A. Snoch,∗19 A. Sochocka,∗11 T. Sumikama,∗4 H. Suzuki,∗4 D. Suzuki,∗4∗4∗2
H. Takeda, S. Tangwancharoen, Y. Togano,∗13,∗4 Z. G. Xiao,∗20 S. J. Yennello,∗18,∗21 and Y. Zhang∗20

β = -0.23

11.5

Z =2p /A < 280 MeV/c
T012N1Exp.
AMD0.50p100

d200t3He300

4He

400500600

p /A (MeV/c)
TFig. 1. The yield ratio R21 between two systems 132 Sn +124
Sn and 108 Sn + 112 Sn. Experimental data (markers)
are compared with AMD (shaded area). Inner panel:Isoscaling ﬁt for pT /A < 280 MeV/c.

β = −0.23 (inner panel of Fig. 1). On the other hand,
the triton and helium R21 values breakdown above thislimit, and the isoscaling phenomenon vanishes. Thissuggests that high pT /A particles come from the nonequilibrated environment.
The antisymmetrized molecular dynamics (AMD)model5,6) is employed with Skyrme SLy4 effective interaction and symmetry energy slope parameter L =46 MeV. The AMD result qualitatively explains isoscaling for pT /A < 280 even though AMD is a dynamical
model. However, AMD underestimate triton R21 and do
not reproduce breakdown of R21 .
References
1) M. B. Tsang et al., Phys. Rev. C 64, 054615 (2001).
2) J. Barney et al., Rev. Sci. Instrum. 92, 063302 (2021).
3) H. Otsu et al., Nucl. Instrum. Methods Phys. Res. B 376,175 (2016).
4) J. W. Lee et al., Nucl. Instrum. Methods Phys. Res. A965, 163840 (2020).
5) A. Ono, Prog. Part. Nucl. Phys. 105, 139 (2019).
6) M. Kaneko et al., Phys. Lett. B 822, 136681 (2021).

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