Research Group for Hadron Nuclear Physics
Group Leader : Makoto Oka
Members : Hiroyuki Sako, Toshiki Maruyama, Shoichi Hasegawa, Susumu Sato, Kiyoshi Tanida,Hitoshi Sugimura, Yudai Ichikawa, Takayasu Sekihara, Hiroyuki Ekawa, Shuhei Hayakawa,Shinji Kinbara, Yoshiyuki Nakada, KenIchi Imai, Shoji Nagamiya, Atsushi Hosaka, EmikoHiyama

Our group has performed 1) experimental studies of exotic
hadrons and nuclei with strangeness and charm, high-density
matter at J-PARC and BNL-RHIC, and 2) theoretical studies ofnuclear matter at low and high densities, and the roles ofstrangeness and charm in nuclear matter and neutron stars.
Through these topics, we study many-body problems of quarks
and hadrons in relation with quantum chromodynamics (QCD).
Hadron physics experiments at J-PARC and Belle
We performed the first run of J-PARC E07 experiment tomeasure double Λ hypernuclei in stopped Ξ− reactions using thehybrid-emulsions-SSD method, where we associate tracks from
SSD (Silicon Strip Detectors) with hits in emulsions. We
irradiated 18 out of 100 emulsions stacks with 𝐾𝐾 − beam fromthe K1.8 beam line at the hadron hall of J-PARC. We haveconfirmed that the hybrid-emulsion-SSD method works asplanned, and expect 10000 Ξ − stopped events in these data
[1,2]. We also analysed the E05 pilot run data. We observed apeak which can be identified as 12ΞBe in 𝐾𝐾 − 12C → 𝐾𝐾 + 𝑋𝑋 reaction.
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We also measured 𝐾𝐾 − 12C → 𝑝𝑝𝑝𝑝 reaction to study 𝐾𝐾
interaction, and the result of the analysis is shown in Fig. 1 [3].
As a preparation of the Hyperon spectrometer for the Hdibaryon search experiment (J-PARC E42), we perform
excitation tests of the Helmholtz-type superconducting magnet
at KEK. The Stage-II request of the E42 experiment will beapproved after our update of the technical design review (TDR).
Results of the E15 experiment of 𝐾𝐾 − 3He → Λ𝑝𝑝𝑝𝑝 reactions [4],and a theoretical analysis [5] for possible 𝐾𝐾 − 𝑝𝑝𝑝𝑝 bound states aregiven in a separate report.
At the Belle detector of the KEK B-factory, we analyzed
spectrum of charm baryon excited states and weak decays ofcharmed baryons. We observed Λ+c → 𝑝𝑝𝐾𝐾 + 𝜋𝜋 − decay in 𝑒𝑒 + 𝑒𝑒 −collisions [6], which is the first observation of a double
Cabibbo-suppressed decay of charmed baryons.
High energy heavy-ion physics at RHIC and J-PARC
The RHIC-PHENIX experiment aims at studies of quark-gluon
plasma. In the 2015-2016 run, we investigated the reactions
Au + Au at nucleon-nucleon center-of-mass energy √𝑠𝑠𝑁𝑁𝑁𝑁 of200 GeV, 𝑑𝑑 + Au at √𝑠𝑠𝑁𝑁𝑁𝑁 of 20, 39, 52, and 200 GeV. It was
the last run of PHENIX. It will be upgraded into sPHENIXexperiment which is to measure jets in 2019.
The J-PARC Heavy-Ion project (J-PARC-HI) aims to explore
QCD phase structures at extremely high baryon density with theworld’s most intense heavy-ion beam. Detailed design of the
dilepton spectrometer and the hypernuclear spectrometer andtheir expected physics performance has been discussed [7]. We
have submitted the Letter-Of-Intent of J-PARC-HI to the JPARC PAC (Program Advisory Committee) in June 2016.
Hadron Theory Research and Theoretical Physics InstituteThe J-PARC experimental programs are quite competitive andhighly regarded internationally, and they rely on strong
theoretical supports. Our theorists benefit from working closelywith experimentalists and have established collaborative
research in multi-strange hadron/nuclear physics, charm hadron
physics, and properties of dense hadronic matter. Much efforts
have been devoted to promote theoretical researches to support
J-PARC experiments. For example, we started the Theoretical
Physics Institute (TPI) at ASRC, aiming to promoteinternational collaborations related to the J-PARC hadron
physics. It is also intended to host cross-disciplinary
collaborations among the theorists in ASRC. We held a series of
TPI Lectures, for which we invited several guest speakers
covering hadron physics, nuclear structure and reactions andcondensed-matter physics.
The Reimei Program and International Collaborations
A Reimei Program on “Advanced Study of New Exotic Hadron
Matter at J-PARC” was successfully carried out with Prof.
Hyun-Chul Kim (Inha Univ., Korea) as the PI. We had a fruitfulresearch collaboration to study heavy quark hadrons and dense
matter physics with heavy-ion collisions. We held three Reimei
workshops: the J-PARC Workshop 2016 “From Exotic Hadronsto QGP” at Inha University in June with 50 participants, theReimei Workshop “Physics of Heavy-ion Collisions at J-PARC”
at ASRC in August with 50 participants, and the Reimei
Workshop “New Exotic Hadron Matter at J-PARC” at Inha
University in October with 57 participants.

Fig.1 Missing mass spectrum for the 𝐾𝐾 − 12C → 𝑝𝑝𝑝𝑝 reaction at

1.8 GeV/c. Experimental data are shown by black points. Fitting
results are indicated with different colors [3].
References[1] H. Ekawa et al., JPS Conf. Proc. 17 (2017) 033002.
[2] S. Hayakawa et al., JPS Conf. Proc. 17 (2017) 033003.
[3] Y. Ichikawa et al., JPS Conf. Proc. 13 (2017) 020007.
[4] Y. Sada et al., Prog. Theor. Exp. Phys. 2016 (2016) 051D01.
[5] T. Sekihara et al., Prog.Theor.Exp.Phys.2016(2016)123D03.
[6] S.B. Yang et al. (Belle Collaboration), Phys. Rev. Lett. 117(2016) 011801.
[7] H. Sako et al., Nucl. Phys. A 956 (2016) 850-853.