Annual Report 2023

  The RCNP Annual Report summarizing our activities in FY2023 is now available.

  A major highlight this year was the first PANDORA (Photo-Absorption of Nuclei and Decay Observation for Reactions in Astrophysics) experiment at RCNP, held in October 2023 under the program number E563. This international collaboration aims to produce precise systematic data of the photo-nuclear absorption cross sections and decay branching ratios for key light nuclei below iron, which are critical for understanding the photo-interactions of Ultra High Energy Cosmic Rays.

At LEPS2, differential cross sections of γp → f0(980)p → π0π0p were measured together with photon beam asymmetries for the first time in the energy range from the threshold to 2320 MeV. The f0(980) photoproduction signal was clearly observed thanks to no contribution from ρ meson photoproduction. The results indicate that a contribution from the t-channel exchange of vector mesons increases at higher energies, and it may suggest a stronger contribution from a q-q_bar component in f0(980).

The data acquisition infrastructure division in RCNP, newly established in 2022, has initiated a collaborative development group called SPADI Alliance for developing a common-use or standardization of the trigger-less streaming readout system. The first implementation of this system in physics experiments E585 and Honor Seminar in July 2023 showed that it enabled data acquisition with more than 100 kcps trigger-equivalent rate at the Grand Raiden spectrometer.

An aerogel Cherenkov counter with a refractive index of n=1.03 was developed and tested for K/p separation in a 3.5 GeV/c beam at the NA61 experiment. Nearly 100% efficiency was achieved using four fine-mesh PMTs, meeting the requirements for the NA61 experiment.

The theory group investigated the effect of nuclear deformation on β decay rates using the Zr isotopes where multiple deformed states compete energetically. Our calculations demonstrated significant changes in decay rates when shape transitions occur with changes in neutron number. A sudden drop of half-lives around N = 74, if observed experimentally, could indicate a shape transition in this region.

Calculations using the HAL QCD method were carried out to study the diquark degrees of freedom in charm baryons on the lattice. Considering a quark-diquark system where a spectator quark is replaced by a spectator static quark was found to be quite fruitful in avoiding uncertainties related to the charm quark mass and separating the diquark mass from interaction energy.

These highlights represent just a small sample of the diverse and high-quality research being conducted at RCNP by our talented researchers and collaborators around the world. We look forward to the new discoveries and insights that the next year will bring as we continue to push the frontiers of nuclear physics.

Sincerely yours,

Takashi Nakano
Director of Research Center for Nuclear Physics