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, Shinhyung KIM, NANAMURA Takuya, ICHIKAWA Masaya, NAKASUGA Satomi,
EBATA Kengo, DODO Taku, HIRATA Hikari, AKAISHI Takaya, MARUYAMA Toshiki,
Philipp GUBLER, SUZUKI Kei, MIAKE Yasuo, TANAKA Kazuhiro, SAKAGUCHI Takao,IMAI KenIchi, NAGAMIYA Shoji, ESUMI ShinIchi, OYAMA Ken

The research goals of the Hadron Nuclear Physics Group are toexperimentally study 1) exotic hadrons and nuclei with strange
and charm quarks, and 2) hot and dense partonic/hadronic matter
at J-PARC (Japan), BNL-RHIC (USA), and Belle (II) (Japan).
Through these studies, we explore many-body problems ofquarks and hadrons in relation to Quantum Chromo Dynamics(QCD).
Hadron experimental studies at J-PARC
On the X-ray spectroscopy of Ξ- atoms, we developed a novel
experimental method with emulsion and germanium detectors [1].
We searched for signals of Ξ--Br and Ξ--Ag atoms in the X-ray
energy spectrum. Although we found no signal, we reduced thebackground level by a factor of 170 [2]. We also proposed anexperiment to search for a Ξ--C atom, which was approved with
Stage-1 status (for its physical significance).
We have analyzed the data for the first experiment to search for
H-dibaryon with the Hyperon Spectrometer. Using the trackreconstruction algorithm developed with the Time Projection
Chamber (TPC), we obtained clear peaks for Λ and Ks, in the pπand π-π- invariant mass spectra, respectively. We demonstrated
clear identification of π and p with the energy deposit in the TPC.
We also proposed a new experiment to study ΣN cusp, which hasbeen approved as Stage-1 status.
We have been making final detector preparations to study Ξ-nucleus for the beam time planned in June 2023.
We studied Σ+p elastic scattering using the data of anexperiment to study of Σ±p scattering [3]. Analyzing 2400
scattering events, 80 times the number of events in previous
experiments, we obtained precise differential cross sections andphase shifts, where the latter are related to the strength of theinteraction. As shown in Fig. 1, the phase shift of Σ+-p scattering
is found to be twice as large as that of p-p scattering, that indicatesstrong repulsive force between Σ+ and p. A press release waspublished for the result.
In the experiment to study Λ(1405) via (K-, n) reaction on thedeuteron target, we obtained a precise pole position of Λ(1405)
in d(K-, n)πΣ reactions [4]. We published a press release for thisresult.

Fig.1: Phase shifts of proton-proton and Σ+-proton scatterings.

We study modification of the φ meson mass with φ decay intoe+e- inside the nucleus at J-PARC. We evaluated the electron
identification performance of Hadron Blind Detectors and LeadGlass Calorimeters with the data of the commissioning run in
2021 [5]. A new experimental proposal of φ→K+K- measurement
has been approved with Stage-1 status. We have developed andtested Multi-gap Resistive Plate Chambers with high-rate
capability and achieved a timing resolution of 74 ps and a
detection efficiency of 95%.
Other research activities
A future heavy-ion beam program at J-PARC (J-PARC-HI) is
proposed to create dense baryonic matter and search for phasestructures in the high-density region of the QCD phase diagram.
In this fiscal year, we submitted “A request to investigate heavyion acceleration” to J-PARC, which started the official
investigation of heavy-ion acceleration at J-PARC. We also
submitted “Future academic promotion plans” for J-PARC-HI
from Univ. of Tsukuba as a representative of the community.
We studied exotic hadrons at Belle and Belle II experiments. In
heavy-ion collisions, we performed the STAR experiment tostudy high-density matter, and made final preparations forIntermediate Silicon Tracker (INTT) for the sPHENIX
experiment to study the quark-gluon plasma at RHIC.
Reimei research programs
We continued the Reimei program “Collaborative research toevaluate QCD vacuum properties at high density from ϕ meson
decay inside the nucleus” starting from JFY2021, led by S. H.
Lee (Yonsei Univ.) to study φ properties inside the nucleus. We
studied the relation between decay kinematics of φ→e+e- and φ→
K+K- decays. We found that φ polarization can be distinguishedin both decays with the decay angle of the daughter particles [6].
In particular with φ→K+K-, both longitudinally and transverselypolarized φ can be clearly distinguished. We held a Reimei
Workshop “Polarization phenomena and Lorentz symmetry
violation in dense matter” at Yonsei University and online with
41 participants in Oct. 2022.
References[1] M. Fujita et al., Nucl. Instrum. Meth. A 1042, 167439 (2022).
[2] M. Fujita et al., Prog. Theor. Exp. Phys. 2022, 123D01 (2022).
[3] T. Nanamura et al., Prog. Theor. Exp. Phys. 2022 093D01(Editor’s Choice).
[4] S. Aikawa, et al., Phys. Lett. B 837, 137637 (2023).
[5] S. Nakasuga, et al., Nucl. Instr. Meth. A 1041 (2022) 167335.
[6] I.W. Park, H. Sako, K. Aoki, P. Gubler and S. H. Lee, Phys.
Rev. D 107, 074033 (2023).