Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 49 (2016)

First commissioning results for SπRIT-TPC
M. Kurata-Nishimura,∗1 G. Jhang,∗3 J. Barney,∗2 J. Estee,∗2 M. Kaneko,∗4 Y. Zhang,∗6∗2 J. W. Lee,∗3P. Lasko,∗5 G. Cerizza,∗2 C. Santamaria,∗2 K. Pelczar,∗5 Y. Kim,∗7 H. Lee,∗7 J. Lukasik,∗5 P. Pawlowski,∗5D. Suzuki,∗1 T. Isobe,∗1 T. Murakami,∗4 W.G. Lynch,∗2 M.B. Tsang,∗2 and for SπRIT-TPC collaboration
tral collision events.
The reaction vertex was extrapolated from tracks
event by event and the Z-vertex of 84% events wasfound around the target within 5mm in sigma for highmultiplicity events. The event ratio originating fromthe target depended on the trigger conditions.
The first commissioning of SπRIT-TPC was successfully performed outside of the SAMURAI magnet. The
high multiplicity track events were reconstructed andthe reaction vertex was found around the target. The
gating-grid driver worked with the fast trigger provided by three trigger arrays. Modification of readout
electronics and optimization of trigger system is underinvestigation for coming physics run.

The aim of the SAMURAI Pion-Reconstruction andIon-Tracker Time-Projection Chamber (SπRIT-TPC)
1)
project is to constrain the symmetry energy term in
the nuclear-matter equation of state (EOS) at supersaturation density. It is proposed to compare π + /π −production ratio among various isospin asymmetry environments combining different unstable Sn beams andstable Sn targets in SAMURAI.
The first commissioning run using 79 Se beam was
performed outside of the SAMURAI magnet in fall2015. The performance of SπRIT-TPC and trigger
systems were evaluated. Results revealed necessarymodifications for upcoming physics campaign.
For the commissioning, the SπRIT-TPC was placed
about 7 m away from the center of the SAMURAI
magnet and lined up on 60 deg with the 79 Se secondary
beam. Two targets of 0.5 mm natural Sn foil and 9 mmaluminum plate were mounted on a ladder in front of
the TPC field cage window.
The overall readout system3) was prepared and three
types of trigger arrays composed by plastic countersread by MPPCs were installed for opening a gating griddriver. (1) KATANA (KrAkow Trigger Array with amplitude discrimiNAtion) was placed at the exit window
to reject the non reacting beam. (2) The Multiplicity
Trigger Array4) was placed on the both sides of TPC toselect high multiplicity events. (3) The active collimators was mounted in front of the target to reject beams
hitting the target frame. The reaction trigger was provided by a start counter signal, no hit on the active
collimator, low energy deposit in KATANA, and multiple hits on Multiplicity Trigger Array. The trigger
condition was controlled through a trigger logic board.
The analysis framework, SπRITROOT5) , has beendeveloped for SπRIT-TPC experiment. Using thiscode, a typical high multiplicity 3D event display isshown in Fig.1. The straight tracks were reconstructedeven in dense track regions just after the target.
The total number of reconstructed tracks per event
was plotted for two different multiplicity selections
with KATANA and Multiplicity Trigger Array inFig.2. Higher multiplicity requirement resulted inhigher multiplicity track events corresponding to cen∗1
∗3
∗2

∗4
∗6
∗5
∗7Fig. 1. A typical high multiplicity track event producedwith 79 Se on Sn (nat.) target. The target was located
8.9 mm upstream from the field cage window.

Fig. 2. The total multiplicity in the TPC gated on the multiplicity in the ancillary detectors KATANA and Multiplicity Trigger Array

RIKEN Nishina Center
Department of Physics, Korea Universtiy
National Superconducting Cyclotron Laboratory and Department of Physics and Astronomy, Michigan State University
Department of Physics, Kyoto University
Department of Physics,Tsinghua University
Institute of Nuclear Physics, PAN
Institute for Basic Science, Korea

References
1) R. Shane at al.: Nucl. Instr. Meth. A 784 (2015) 513.
2) M.B. Tsang et al; Phys. Rev. Lett. bf 102 (2009) 122701.
3) T. Isobe et al,; in this report.
4) M. Kaneko et al,; in this report.
5) G. Jhang et al,; in this report.

- 43 -