-ray spectroscopy of hypernuclei; Recent results and prospect at J-PARC

Tamura, Hirokazu*; Ekawa, Hiroyuki; Hasegawa, Shoichi   ; Hayakawa, Shuhei; Hosomi, Kenji  ; Hwang, S.; Ichikawa, Yudai   ; Imai, Kenichi; Sako, Hiroyuki   ; Sato, Susumu  ; Sugimura, Hitoshi; Tanida, Kiyoshi   ; J-PARC E13 Collaboration*; 42 of others*

The present status and future prospects of precision -ray spectroscopy of hypernuclei are described. A new experiment (J-PARC E13) has been performed at the J-PARC K1.8 line employing a newly-developed germanium (Ge) detector array, Hyperball-J, via the reaction on He and F targets. This is the first study of -shell and -shell hypernuclei with Ge detectors. The He target spectrum exhibited a -ray peak of at MeV. Compared with the energy ( MeV) of the corresponding transition for the mirror hypernucleus, , the present result clearly indicates a large charge symmetry breaking (CSB) effect. This decisive data for CSB allows a stringent test of baryon-baryon interaction models. As for the F target run, a preliminary spectrum shows several -ray peaks assigned to transitions. Future plans of -ray spectroscopy are also discussed.