Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 50 (2017)

Measurement of Pion Multiplicities in Asymmetric Sn Reactions Using
the SπRIT Time Projection Chamber
J. Barney,∗1,∗2 G. Cerizza,∗1,∗2 J. Estee,∗1,∗2 B. Hong,∗3 T. Isobe,∗2 G. Jhang,∗3,∗2 M. Kaneko,∗2,∗4M. Kurata-Nishimura,∗2 P. Lasko,∗5,∗6,∗2 H. S. Lee,∗7 J. W. Lee,∗3,∗2 J. Łukasik,∗5 W.G. Lynch,∗1A.B. McIntosh,∗8 T. Murakami,∗4,∗2 P. Pawłowski,∗5,∗2 K. Pelczar,∗6 H. Sakurai,∗2 C. Santamaria,∗1,∗2R. Shane,∗1 D. Suzuki,∗2 M. B. Tsang,∗1 S.J. Yennello,∗8 Z.G. Xiao,∗9,∗2 Y. Zhang,∗9,∗2and the SπRIT and NeuLAND collaborations
Determination of the nuclear Equation of State(EOS) is of fundamental importance in nuclear physics.
To constrain the symmetry energy term of the EOS
at supra-saturation density, a series of measurements
were proposed with neutron rich and neutron deﬁcient
Sn isotopes at about 300 MeV/U. Experimental observables include pion production, n vs. p emission
and diﬀerential ﬂow, and t and 3 He emission. An international collaboration initially started and fundedby the groups from Michigan State University, Kyoto
University, and RIKEN, which was later joined by collaborators from Korea, Poland, and China, completed
the construction of the SπRIT Time Projection Chamber (TPC)1) , designed to measure pions as well as lightcharge particles emitted in heavy ion collisions.

reject beam particles which do not hit the target. Thetrigger condition requires a multiplicity of 4 or greaterin the Kyoto Array, enhancing central collision events.
The NeuLAND neutron detection system (not shown)is used to measure neutrons emitted in the reactions.
The 2016 run of the SπRIT TPC is shown in Tab. 1.
A commissioning run was performed in April 2016 with
the TPC inside the SAMURAI spectrometer at the 0◦
conﬁguration, set to 0.5 T. A 132 Sn secondary beam
was impinged on a 0.5 mm thick natural Sn target.
The dedicated commissioning run inside the SAMURAI magnet allowed particle identiﬁcation with thecomplete version of the SπRITROOT analysis framework. The ﬁrst experiment consisted of neutron deﬁcient 108 Sn and stable 112 Sn secondary beams impinging on 0.836 mm thick 112 Sn and 0.828 mm thick 124 Sntargets, respectively. The second experiment consistedof neutron rich 132 Sn and stable 124 Sn secondary beams
impinging on 0.828 mm thick 124 Sn and 0.836 mm
thick 112 Sn targets, respectively. Additionally, a cocktail beam of charge Z = 1 − 3 was produced at 100 and300 MeV/U, providing reference points to calibrate theenergy loss measurements with the TPC.
Table 1. Spring Campaign with the SπRIT TPC
Beam132
Sn108
Sn112
Sn124
Sn132
Sn
Z=1-3 cocktailFig. 1. The SπRIT TPC inside the SAMURAI magnet withancillary detectors outlined.

Figure 1 shows the experimental set up, including
some ancillary devices. The Kyoto Array, consistingof two arrays of 30 scintillators each, are positioned on
the beam left and beam right sides of the TPC, while
the Krakow Array for Triggering with Amplitude discrimiNAtion (KATANA)2) , consisting of 12 thick scintillators and three veto paddles, is positioned on thedownstream side. Three KATANA beam veto scintillator paddles are used to reject unreacted beam particles. A veto collimator with 2x2 scintillators (notshown) is positioned 22 cm upstream of the target to
∗1
∗2
∗3
∗4
∗5
∗6
∗7
∗8
∗9Reaction TargetnatSn112
Sn124
Sn112
Sn124
SnNo Target

Triggered Events∼ 2.0 × 106∼ 1.0 × 107∼ 5.9 × 106∼ 5.3 × 106∼ 1.0 × 107∼ 6.8 × 105

Over 250 TB of data were collected in the 2016 experimental campaign, and analysis of this data is ongoing. The experiment represents a new measurement
to constrain the symmetry energy term of the EOS.
This work is supported by the U.S. DOE underGrant Nos. DE-SC0004835, DE-SC0014530, DENA0002923, US NSF Grant No. PHY-1565546, theJapanese MEXT KAKENHI grant No. 24105004 andby the Polish National Science Center (NCN), under contract Nos. UMO-2013/09/B/ST2/04064 andUMO-2013/10/M/ST2/00624.

NSCL and Dept. of Phys. & Ast., Michigan State University
RIKEN Nishina Center
Department of Physics, Korea University
Department of Physics, Kyoto University
IFJ PAN, Kraków
Jagiellonian University, Kraków
Rare Isotope Science Project, Institute for Basic Science
Cyclotron Institute, Texas A&M University
Department of Physics, Tsinghua University

Referencesal., Nucl.
1) R. Shane et al.:Nucl. Instr.
Instr. Meth. A 784, 513 (2015).
Lasko etet al.:al., arXiv:1610.06682 (2016).
2) P. Lasko- 49 -