RIBF Nuclear Physics Seminar

Study of charge symmetry breaking in A=4 hypernuclear system

201 (RIBF Hall)



=Date and Place=
Feb. 7th(Tue.), 13:30~ at RIBF Hall(room 201)

Dr.Takeshi Yamamoto

Study of charge symmetry breaking in A=4 hypernuclear system        via the gamma-ray spectroscopy experiment at J-PARC

The charge symmetry breaking (CSB) effect reported in the A=4 mirror hypernuclei (4ΛH and 4ΛHe) is one of the hot topics in strangeness nuclear physics. Unexpectedly large CSB effect reported in old experiments was long standing puzzle and may become key to understand ΛN interaction. High accuracy data, with modern experimental technique, was long time awaited to confirm existence of CSB effect. Precise gamma-ray spectroscopy with an energy resolution of a few keV is a powerful tool to investigate such an effect. In fact, a gamma-ray spectroscopy study of 4ΛHe was performed at the J-PARC K1.8 beam line (J-PARC E13, 2015) for this purpose. 4ΛHe hypernuclei were produced by the direct 4He(K−, π−)4ΛHe reaction with a high intensity kaon beam. Gamma rays were measured with a newly developed Ge detector array, Hyperball-J. The excitation energy of first excited state of 4ΛHe(1+) was successfully determined to be 1.406±0.004 MeV. By comparing to that of the mirror hypernucleus (4ΛH) from previous old studies, we confirmed the existence of CSB effect and its spin dependence. Our next step is a more precise and conclusive measurement of the excitation energy of 4ΛH(1+) to experimentally establish the A=4 mirror hypernuclei system. We are planning gamma-ray spectroscopy of 4ΛH at the J-PARC K1.1 beam line (J-PARC E63) via the 7Li(K−, π−) reaction. The results of the gamma-ray spectroscopy of 4Λ He and an outline of the future experiment will be given.