Annual Report 2021

We are pleased to release a new RCNP Annual Report on our activities in FY2021.

　In this fiscal year, the AVF cyclotron upgrade was completed. Commissioning of the accelerator for the resumption of experiments at the cyclotron facility as soon as possible is rapidly underway. Progress was also made in the development of the beamline that would receive the beam. The MuSIC muon group has been continuing the beamline maintenance and developing new experimental apparatuses such as a beam tracking chamber for the 2-dimensional elemental mapping in the non-destructive muonic X-ray analysis in order to resume joint-use experiments in FY2022.

　At J-PARC, preparations for the E50 experiment are steadily underway to elucidate diquark correlations in hadrons. Two topics covered in 2021 Highlights relate to detector development for the E50 experiment. One of the big challenges of the E50 experiment is particle identification in a wide momentum range. Prototype of the threshold-type Cherenkov PID detector with a low index of 1.007 was evaluated at the LEPS2 facility. The results shows that the misidentification probability of a kaon as a pion is less than 1% while the pion-detection efficiency of greater than 95% in the momentum range of 2 to 4 GeV/c. Another challenge is high-rate capability. In the E50 experiment, a high-intensity pion beam of 30 MHz will be used. Therefore, the detectors irradiated by the high-intensity beam are required to stable operation under the high counting-rate condition of 1 MHz/mm. Scintillating fiber tracks will be used to detect particle tracks near the experimental target instead of a wire chamber because of potentially good rate capability. Test experiment with high-intensity beams was performed at the Research Center for Electron Photon Science, Tohoku University using two types of ASICs, called CITIROC1A and PETIROC2A for the readout of MPPC. Both ASICs shows high performance which satisfies the required performance for the charm baryon spectroscopy experiment.

　For an experiment in the very low energy region, the MAIKo active target has been developed to study production rate of 12C in the universe through the triple-alpha reaction. An experiment at OCTAVIAN demonstrated clear identification of the Hoyle state with the measured cross section which was consistent with the previous one. Encouraged by this success, construction of a new active target, MAIKo+, is in progress to improve the statistics by a factor of 10.

　The theoretical group reported the study on nucleon-hyperon interaction from Lattice QCD near the physical point, which is important to understand the high-density objects such as neutron stars. Progress report on the Z3-symmetric QCD was also presented. Although the effects of the dynamical quarks break the Z3-symmetry, the symmetry can be restored in three flavor QCD with symmetric quark masses by introducing flavor-dependent imaginary chemical potential. Further progress of the study may give an insight into the property of the confinement-decommitment transition at low temperature and finite density.

Sincerely yours,

Takashi Nakano
Director of Research Center for Nuclear Physics