Research Group for Hadron Nuclear Physics

Group Leader : TAMURA Hirokazu
Members : SAKO Hiroyuki, HASEGAWA Shoichi, TANIDA Kiyoshi, SATO Susumu,ICHIKAWA Yudai, HASHIMOTO Tadashi, NARUKI Megumi, YAMAMOTO Takeshi, FUJITA
Manami, NANAMURA Takuya, NAKASUGA Satomi, DODO Taku, ICHIKAWA Masaya,
MARUYAMA Toshiki, Philipp GUBLER, SUZUKI Kei, MIAKE Yasuo, TANAKA Kazuhiro,
IMAI KenIchi, NAGAMIYA Shoji, ESUMI ShinIchi, OYAMA Ken

The research objectives of the Hadron Nuclear Physics Groupare experimental studies of 1) exotic hadrons and nuclei withstrange and charm quarks and 2) hot and dense partonic/hadronicmatter at J-PARC, BNL-RHIC, and Belle (II). Through these
topics, we investigate many-body problems of quarks andhadrons in relation to Quantum Chromo Dynamics (QCD).
Hadron experimental studies at J-PARC
We completed the J-PARC E03 experiment (X-ray
spectroscopy with Ξ- atom) in Apr. 2021 [1]. We collected 95billion K- irradiated events, which correspond to 95% of theplanned statistics. The analysis of the X-ray spectrum isunderway.
We also completed the first experiment E42 (Search for Hdibaryon) to use the Hyperon Spectrometer in June 2021, with
175 billion K- irradiated events. The Time Projection Chamber(TPC) has been stably operated with good 3-dimensional tracking
performance as shown in Fig. 1. The efficiency of 94% isachieved. Calibration of the TPC such as the baseline correction
and the drift time correction is being performed.
We analyzed the E40 (Study of Σ±p scattering) data, andpublished two papers for Σ-p elastic [1] and Σ-p→Λn inelastic [2]scatterings. A press release is also published for the former result.
For details, refer to the research highlight article in this volume.
The Transition Edge Sensor detector developed for the X-ray
spectroscopy for Kaonic atoms at K1.8 beamline was applied formuonic atoms and detailed deexcitation processes were unveiled[3]. We issued a press release for this result.

Fig.1: An interaction event of the TPC at J-PARC E42 experiment.

J-PARC E16 aims at studying in-medium modification of theφ meson spectrum through φ decay into e+e- inside the nucleus. A
commissioning run of E16 was performed in May-June 2021. We
evaluated the electron identification and pion rejection
performance of Hadron Blind Detectors and Lead Glass
Calorimeters. We also tested time-of-flight measurements withprototype Multi-gap Resistive Plate Chamber (MRPC) and a starttiming counter for charged hadron identification for the φ→K+Kexperiment (P88 below). We also developed a high-rate capable
MRPC by heating glass sheets and confirmed improvement of thetiming resolution by increasing temperature at LEPS2. We
submitted a proposal for the φ→K+K- measurement to J-PARC
Program Advisory Committee (PAC) in June 2021, and tworeviews were held in July 2021 and Jan. 2022. The proposal (P88)
is going to be approved for Stage-I status (physics importance) inearly JFY 2022.
Other research activities
We propose a future heavy-ion beam program at J-PARC (JPARC-HI) to create dense baryonic matter to search for a phaseboundary and the QCD critical point in the QCD phase diagram.
We submitted the first experimental proposal (P89) to J-PARC
PAC in July 2021, which aims to measure the temperature ofthermal photons with e+e- pairs at the J-PARC E16 spectrometerwith detector upgraded for heavy-ion collisions to search for thephase transition. The proposal submission accelerated thediscussions for J-PARC-HI in J-PARC center and JAEA.
We also studied exotic hadrons at Belle and Belle IIexperiments, and studied high-density matter at the STAR
experiment and developed silicon-strip detectors for sPHENIX
experiment at RHIC.
Reimei research programs
The Reimei research program “Systems with two strange quarks
at FAIR and J-PARC” continued since JFY 2020 to strengthen thecooperation between scientists working at J-PARC and FAIR, theonly two facilities in the world for the two-strange quark systems,
through an international collaboration with Prof. J. Pochodzalla(Univ. of Mainz). We continued weekly seminars between ourReimei research program and the THEIA program funded by EU,
including discussions on research plans to search for X-rays fromheavy hyperatoms for the PANDA experiment at FAIR and JPARC experiments.
We proposed another Reimei program “Collaborative research
to evaluate QCD vacuum properties at high density from ϕ meson
decay inside the nucleus”. In this program, we collaborate withtheorists led by S. H. Lee (Yonsei Univ.) and exprimentalists at JPARC to study φ properties inside the nucleus. We developed
theoretical model for J-PARC P88 to support the review. We helda Reimei Workshop “Hadrons in dense matter at J-PARC” online
with about 100 participants in Feb. 2022.
References[1] K. Miwa et al., Phys. Rev. C 104, 045204 (2021).
[2] K. Miwa et al., Phys. Rev. Lett. 128, 072501 (2022).
[3] T. Okumura et al., Phys. Rev. Lett. 125, 053001 (2021).