Research Group for Nuclear and Hadron Physics
Group Leader: Ken-ichi Imai
Members: Toshiki Maruyama, Hiroyuki Sako, Susumu Sato, Shoichi Hasegawa, SanghoonHwang, Kenji Hosomi, Hitoshi Sugimura, Yudai Ichikawa, Hiroyuki Ekawa, Tong-Gyu Lee,
Koichiro Nishikawa, Shoji Nagamiya, Kiyoshi Tanida, Kyoichiro Ozawa, and Makoto Oka

The research objectives of Research Group for Nuclear andHadron Physics are 1) experimental study of exotic hadrons andnuclei with strangeness and charm at J-PARC and BNL-RHIC,2) research and development of high rate particle detectors suchas a time projection chamber, silicon strip detectors, andscintillation fiber trackers, 3) theoretical study of nuclear matterat low and high densities and the role of strangeness in nuclear
matter and neutron stars. Through these topics, we study manybody problems of quarks and hadrons in relation with QCD.
Hadron physics experiments at J-PARC
Due to the radiation accident at the hadron experimental hallin May 2013, the hadron beam has been postponed to April
2015, when E13 (gamma spectroscopy in 4H and 19F
hypernuclei) will be resumed. Thus we did not have beam in2014. We contributed to renovation of the hadron experimental
hall for air tightness between the hadron beam line and theexperimental hall, to improve readout rates for the interaction
monitor of the secondary beam production target and the beamprofile monitor in the hadron beam line.
We analyzed data of E27 experiment, to measure the smallest
kaonic nucleus, a K-pp bound state in the d(+,K+) reactions. In
inclusive analysis which measured only + and K+, we observeda N cusp structure which is almost consistent with previous
data [1]. We also observed a mass shift in the peak of Y*[(1385) and (1405)] by -32.4 MeV/c2. This may be due toY*N final state interactions. In order to investigate the origin,further experimental and theoretical studies are necessary [1]. In
the exclusive analysis where two protons are required, weobserved K-pp-like structure in the Σ0p spectrum for the firsttime as shown in Fig. 1 [2]. The K-pp binding energy and thewidth are estimated to be 95 MeV and 162 MeV, respectively.
We observed a deeply bound state of - -nucleus bound state(-14N) for the first time in a new emulsion overall scan method
for KEK-E373 experiment [3], from  produced in 12C(K-, K+)
reactions and captured in emulsion atoms.
Research and development for high rate particle detectors
We have developed detectors for E03, E07, E42, and E45
experiments such as Beam Hodoscope (BH), Beam Aerogel
Cherenkov counter (BAC), Proton Veto Aerogel Cherenkov
counter (PVAC), and Charge Hodoscope (CH). We evaluatedtheir performance in the test beam experiment at ELPH inTohoku University. Time-Of-Flight counter (TOF) has been
also constructed. The final TPC (HypTPC) with readout pads,GEMs, the gating grid, and a test field cage with a short drift
length has been built and tested with radioactive sources. We
design the final field cage and the target holder, based onelectric field calculations which achieve electric field uniformityof 10-3 level. The test results of the prototype TPC and Silicon
Strip Detectors (SSD) were published in Ref. [4, 5]. The readout
electronic system based on GET (General Electronics for TPC)
has been developed for HypTPC. We added new functions forfast clear in AD conversion and to send fast clear and secondlevel trigger signals, and event-tag information from the JPARC DAQ system.
High energy heavy-ion physics at RHIC and J-PARC
The RHIC-PHENIX experiment aims at studies of partonic
matter called quark-gluon plasma. In 2014, we took Au+Au
collision data at nucleon-nucleon center-of-mass energies of 15
and 200 GeV and 3He+Au data at 200 GeV. More than 80% ofthe vertex pixel detector was functional, which has beendeveloped by JAEA and RIKEN to measure the secondary
vertex of heavy-flavor hadrons.
A future heavy-ion program at J-PARC aims at exploring
phase structures and hadron properties at the baryon density ashigh as neutron stars. We are developing a plan for the whitepaper. The acceleration scheme is being designed using existing
3-GeV Rapid-Cycling Synchrotron (RCS) and the Main Ring
(MR). We have also designed a large acceptance spectrometerfor hadron and lepton measurements in heavy-ion collisions [6].
Theoretical study of nuclear matter
We have studied nuclear matter in compact stars. In particular,competition between hyperon mixture and kaon condensation
has been studied within a relativistic mean field model.
Depending on the kaon potential,  and kaon may coexist in
uniform matter. However,  vanishes when kaons appear inuniform matter. Currently, the case of inhomogeneous matterwith pasta structures is studied.

Fig.1 Missing mass spectrum of the d(+,K+) reaction with two-proton
coincidence for p branch events.

References[1] Y. Ichikawa, et al., Prog. Theor. Exp. Phys. 101D03 (2014).
[2] Y. Ichikawa, et al., Prog. Theor. Exp. Phys. 021D01 (2015).
[3] K. Nakazawa, et al, Prog. Theor. Exp. Phys. 033D02 (2015).
[4] H. Sako, et al., Nucl. Instrum. Meth. A763, 65 (2014).
[5] R. Kiuchi, et al., Nucl. Instrum. Meth. A763, 399 (2014).
[6] H. Sako, et al., Nucl. Phys. A931, 1158 (2014).