Ⅱ-9. Instrumentation

RIKEN Accel. Prog. Rep. 50 (2017)

Calibration of the SπRIT TPC with light fragments
J. Estee,∗1,∗3 J. Barney,∗1,∗3 G. Cerizza,∗1,∗3 B. Hong,∗2 T. Isobe,∗3 G. Jhang,∗2,∗3 M. Kaneko,∗4,∗3M. Kurata-Nishimura,∗3 P. Lasko,∗5,∗3 J. W. Lee,∗2 J. Lukasik,∗5 W.G. Lynch,∗1 A.B. McIntosh,∗6T. Murakami,∗4,∗3 P. Pawlowski,∗5,∗3 K. Pelczar,∗8 C. Santamaria,∗1,∗3 D. Suzuki,∗3 M. B. Tsang,∗1S.J. Yennello,∗6 Y. Zhang,∗7,∗3 and the SπRIT collaboration
The SAMURAI Pion-Reconstruction and IonTracker Time-Projection Chamber (SπRIT-TPC)1)
was constructed to measure pions and light particle
fragments resulting from heavy ion collisions. While
the symmetry energy of the nuclear Equation of Stateis constrained at sub-saturation densities, large theoretical uncertainties still exist above nuclear saturation
density. In an eﬀort to constrain the symmetry energy
at high densities, two experiments were performed at
RIKEN in the spring of 2016 with the TPC inserted
into the SAMURAI magnet.
To calibrate the gain of the TPC, a ”cocktail” beamof (p,d,t,3 He,4 He,6 Li) light fragments was tuned fortwo diﬀerent Bρ settings. The BigRIPS fragment separator was able to provide the species listed in Table 1with a momentum resolution of about 0.8% as estimated by LISE++. Because the momentum of eachparticle was well deﬁned, we can also determine theenergy loss distribution of each particle species.

many readout pads1) . Thus, the energy loss of eachtrack is broken up into smaller analyzed segments orclusters. The straggling function for a 903.63 MeV/cproton was created with a Monte Carlo simulation,and is shown as a blue curve in Fig. 1. To calibrate
the TPC, we assign the energy deposited value D to ameasured ADC value Q. We assume a linear relationship and minimize Pearson’s χ2 to ﬁt the measured
straggling function to the theoretical Bichsel straggling
function yielding the relationship:
D = 0.45 ∗ Q + 0.48

(1)

The red curve in Fig. 1 shows the calibrated experimental straggling function of protons at 903.63 MeV/c.

Table 1. Mean momentum and momentum resolution fromthe BigRIPS separator as predicted by LISE++.
Particlepdt
3
He4He
6Limomentum [MeV/c]
903.6
886.9
886.9
1795.71782.92652.2dpp[%]
0.77
0.78
0.82
0.78
0.80
0.82

The energy loss distribution of a particle depends
not only on a particle’s momentum, but also on theanalyzed segment length and is explained in extensive
Such a technique is implemented indetail in Ref.1)1.. Suchother TPC’s such as STAR and ALICE2) . For ouranalysis, a C++ version of the Bichsel’s FORTRAN
code, in Ref.3)3,, was made and the resulting straggling
functions were compared to the original Bichsel code
to check for accuracy.
As the particle traverses the detection gas volume,the energy deposited is ampliﬁed and recorded over∗1∗2∗3∗4∗5∗6∗7∗8

NSCL and Dept. of Phys. and Ast., Michigan State University
Department of Physics, Korea University
RIKEN Nishina Center
Department of Physics, Kyoto University
IFJ PAN, Kraków
Dept. of Physics and Astronomy, Texas A&M University
Department of Physics, Tsinghua University
Faculty of Physics, Astronomy and Applied Computer Science, Jagiellonian UniversityFig. 1. Fitted TPC data and the Bichsel straggling function
for P-10 gas over a track segment length of 1.2cm. Bin
width is 10 [eV/cm]

In summary, good agreement between the energy
loss distribution of the TPC and the expected Bichsel curve was found for the protons. In the near future, other particle species will be analyzed as well as
the particles produced in the second Bρ setting which
provides higher momentum values.
This work is supported by the U.S. Departmentof Energy under Grant Nos. DE-SC0004835, DESC0014530, DE-NA0002923, US National ScienceFoundation Grant No. PHY-1565546 and the Japanese
MEXT KAKENHI (Grant-in-Aid for Scientiﬁc Research on Innovative Areas) grant No. 24105004.
References
1) R. Shane et al. Nucl. Instr. Meth. A 784, (2015) 513.
2) H. Bichsel Nucl. Instr. Meth. A 562, (2006) 154.
3) Original code found under ”Current research” sectionof home page http://faculty.washington.edu/hbichsel/- 175 -