Research Group for Hadron Physics
Group Leader : Kenichi ImaiMembers : Toshiki Maruyama, Hiroyuki Sako, Susumu Sato, Shoichi Hasegawa, Kenji Hosomi,Hitoshi Sugimura, Minoru Okamoto, Ton-Gyu Lee, Yudai Ichikawa, Sanghoon Hwang,
Ryuta Kiuchi, Kiyoshi Tanida, Shoji Nagamiya

The objectives of Research Group for Hadron Physics are:1) experimental study of exotic hadrons and nuclei withstrangeness and charm at J-PARC and BNL-RHIC, 2) researchand development of new high rate particle detectors such as asilicon strip detector, a scintillation fiber tracker and a time
projection chamber, 3) theoretical study of nuclear matter athigh and low 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.
In 2013, we started an experiment on -spectroscopy ofhypernuclei (E13) in May. During the commissioning of theexperiment, a gold target was melt because of unexpected
intense pulsed proton beam, and radioactive isotopes werereleased to the Hadron Hall and environment. The experiments
at J-PARC are, unfortunately, postponed to the next year due tothe investigation of the accident and the construction ofadditional safety mechanism and shielding for the target, beamline and the Hadron Hall. We have contributed to these works.
The data analyses of the two experiments, search for H
hypernucleus (E10) and search forstate (E27), have beenperformed. The result of E10 was published [1] and is described
as a research highlight in this annual report. Figure 1 shows apreliminary result of E27 suggesting a possible evidence of thestate which was reported at Hadron2013 conference [2].
Detector R&D and Time Projection Chamber (TPC)
We have carried out R&D of a silicon strip detector (SSD),
scintillating fiber tracker and time projection chamber (TPC) for
hadron experiments with high intensity beams at J-PARC. A
key word of the R&D is high rate capability. The SSDs andfiber trackers were successfully used at the rate of more than
10 pions/spill in the E10 experiment. The study of the SSD issummarized recently [3]. Intensive studies of the TPC wereperformed with prototype TPC [4]. We have confirmed the TPC
can be operated at the rate of more than 10 particles/sec. Basedon the studies, we have started the construction of the full size
TPC (sensitive volume of 50 cm in diameter and 50 cm high). It
has 3 layers of GEM (Gas Electron Multiplier) sheet and about
6000 readout pads of which width is 2.5 mm. It is designed todetect short-life hyperons as well as other charged particles
emitted from the target. It will be used for H-dibaryon searchexperiment (E42) and others at J-PARC.
High energy heavy ion physics at RHIC and J-PARC
We took a part in the data taking of polarized proton-proton
collisions and Au-Au collisions at RHIC to study phase diagramof hadron-quark matter, and contributed to the installation andcommissioning of vertex detectors in PHENIX.
We led a working group to study possible scheme of theacceleration of heavy ions at J-PARC and its physics possibility.
Uranium beams at maximum energy at J-PARC can create

nuclear matter with the highest baryon density achievable withheavy ion collisions. Phase transition to quark-gluon matter athigh baryon density is now a hot topic since the quark-gluonphase was confirmed at high temperature and very low baryon
density at RHIC and LHC. For further discussion, we organized
an international workshop on J-PARC heavy ion program. The
goal of the current works is to write a proposal of J-PARC
heavy ion physics.
Theoretical study of nuclear matterIn our study of inhomogeneous structures of liquid-gas
mixed phase of nuclear matter relevant to the neutron star crusts,
we have employed our fully three-dimensional mean-fieldmodel [5]. By using the deformation energy of the ground stateof matter obtained in our new framework, we calculated theshear moduli of crystals of nuclear droplets in neutron gas,
which indicates the mechanical strength of neutron star crusts.
As a preliminary result, we pointed out that the shear modulus
obtained in our full calculation is smaller than that of theconventional simplified calculation, due to the Coulomb
screening and finite-size effects.
The properties of collective excitations of an inhomogeneouschiral phase whose appearance is suggested in quark matter at
finite baryon densities have also been studied. We have foundthat some excitation modes, on the exotic ground state withspiral and wavy geometries, have an anisotropic dispersion
relation.

Fig.1 Missing mass spectrum for,reaction at 1.7GeV/
shown as a ratio of the spectrum with proton detection and thatwithout protons (proton coincidence probability). A possible
bound state. A
origin of a peak around 2.3GeV/ is thesharp peak at 2.13GeV/ is well known Σ -Λ cusp.

References[1] H. Sugimura et al., Phys. Lett. B729, 39 (2014).
[2] Y. Ichikawa et al., Proceedings of Science 181, (2014).
[3] R. Kiuchi et al., submitted to Nucl. Instr. & Methods A.
[4] H. Sako et al., submitted to Nucl. Instr. & Methods A.
[5] M. Okamoto et al., Phys. Lett. B713, 284 (2012); Phys. Rev.
C 88, 025801 (2013)