Ⅱ-1. Nuclear Physics

RIKEN Accel. Prog. Rep. 51 (2018)

Track reconstruction of recoil particles in CAT-S at RIBF113:
132
Sn(d,d’) measurement
S. Ota,∗1 H. Tokieda,∗1 C. Iwamoto,∗1 M. Dozono,∗1 U. Garg,∗2 S. Hayakawa,∗1 K. Kawata,∗1 N. Kitamura,∗1M. Kobayashi,∗1 S. Masuoka,∗1 S. Michimasa,∗1 A. Obertelli,∗3,∗4 D. Suzuki,∗4 R. Yokoyama,∗1 J. Zenihiro,∗4H. Baba,∗4 O. Beliuskina,∗1 S. Chebotaryov,∗4 P. Egelhof,∗5 T. Harada,∗6 M. N. Harakeh,∗7 K. Howard∗2N. Imai,∗1 M. Itoh,∗8 Y. Kiyokawa,∗1 C. S. Lee,∗1 Y. Maeda,∗9 Y. Matsuda,∗8 E. Milman,∗4 V. Panin,∗4
H. Sakaguchi,∗10 P. Schrock,∗1 S. Shimoura,∗1 L. Stuhl,∗4 M. Takaki,∗1 K. Taniue,∗9 S. Terashima,∗11T. Uesaka,∗4 Y. N. Watanabe,∗12 K. Wimmer,∗1,∗4,∗12 K. Yako,∗1 Y. Yamaguchi,∗1 Z. Yang,∗4 and K. Yoneda∗4The equation of state (EoS) of nuclear matter not
only governs the femto-scale quantum many-body system, namely nuclei, but also plays an important role inthe structure of neutron stars and in supernova phenomena. In particular, the EoS of isospin asymmetric nuclear matter has attracted much interest fromthe viewpoint of the existence of heavy neutron stars.
The asymmetric term of incompressibility, Kτ , can bea benchmark for various EoSs because it can be directly deduced from the energies of the isoscalar giant
monopole resonance (ISGMR) measured along an isotopic chain, such as tin isotopes.1) The present valueof Kτ is −550±100 MeV and its error is larger thanthose of other parameters of the EoS. In order to improve the Kτ value, the measurement on the isotopic
chain should be extended to unstable nuclei. A doubly
magic tin isotope, 132 Sn, has been chosen as a ﬂagshipfor the measurements of unstable tin isotopes becauseof its large isospin asymmetry and double magic nature. The measurement of deuterium inelastic scattering oﬀ 132 Sn was performed at RIBF in RIKEN. The
typical intensities of the secondary beam at F3 and F7
were 8.5×105 and 3.2×105 particles per second, respectively. The main components of the secondary beam
were 132 Sn, 133 Sb, and 134 Te with purities of 21%, 46%,and 25% at F7, respectively.
The excitation energy and scattering angle inthe center-of-mass frame are extracted by means of
missing-mass spectroscopy, for which the range andangle of the low-energy recoil deuteron must be measured. In order to measure such low-energy recoils,
a gaseous active target system CAT-S2) with 0.4-atm
deuterium gas has been employed as target and detector simultaneously. In this paper, we report thepresent status of track reconstruction for recoil particles stopping in CAT-S. Before the track reconstruc-tion, a cluster of hits as a candidate track is searchedfor. The detailed procedure of track ﬁnding was reported by Tokieda et al.3) Here, we focus on the energy calibration of each pad and track reconstruction
for the hit cluster found by the track-ﬁnding process.
CAT-S has an active are of approximately 10×10cm2 . Primary electrons produced by energy deposition
along the trajectory of the recoil particle drift toward
the THGEM and readout pad. The drift velocity iscurrently assumed to be 1 cm/µs according to the simulation using Garﬁeld for 0.4-atm deuterium gas with
an electric ﬁeld of 1 kV/cm/atm. The lateral diﬀusion
coeﬃcient is assumed to be 0.04 cm1/2 , which yields
a charge spreading of 2 mm in one standard deviation
for a drift length of 25 cm. In the procedure of trackreconstruction, the charge spreading should be taken
into account.
The track reconstruction is performed in a two-foldmanner. First, the track in the plane deﬁned by thedrift direction (Y) and axis perpendicular to beam (X)is deduced by using a linear ﬁt of position in this plane.
The position along the drift direction is calculated fromthe leading-edge timing multiplied by the drift velocity. The position along the X-axis is the centroid ofeach pad. Second, the track in the plane deﬁned by thebeam axis (Z) and the X-axis is reconstracted by ﬁtting
the calculated charges to the measured charges by taking the diﬀusion and the resolution into account. The
second part of track reconstruction requires energy calibration. A set of trial calibration parameters is usedto deduce the realistic energy calibration parameter
after comparing the measured charge with the one calculated from the best-ﬁt track. The charge resolution
can be estimated from the distribution of the diﬀerence
between the measured and calculated charge. The typical charge resolution after correction is less than 10%.
The analyses for particle identiﬁcation, improvementof track reconstruction using iteration, merging beam
particle identiﬁcation and so on are in progress.

∗1

Center for Nuclear Study, the University of Tokyo
Department of Physics, University of Notre Dame
∗3 Le Centre CEA de Saclay∗4 RIKEN Nishina Center∗5 GSI Helmholtzzentrum für Schwerionenforschung GmbH
∗6 Department of Physics, Toho University∗7 KVI, Center for Advanced Radiation Technology∗8 Cyclotron and Radio Isotope Center, Tohoku University∗9 Department of Applied Physics, University of Miyazaki∗10 Research Center for Nuclear Physics, Osaka University∗11 Dept. of Nucl. Sci. and Tech., Beihang University∗12 Department of Physics, the Univerisity of Tokyo∗2References
1) T. Li et al., Phys. Rev. Lett. 99, 162503 (2007).
2) S. Ota et al., J. Radioanal. Nucl. Chem. 305, 907–911(2015).
3) H. Tokieda et al., CNS Annual Report 2016, 53 (2018).

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