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Report No.

$$gamma$$-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 $$gamma$$-ray spectroscopy of $$Lambda$$ 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 $$(K^-,pi^-)$$ reaction on $$^4$$He and $$^{19}$$F targets. This is the first study of $$s$$-shell and $$sd$$-shell $$Lambda$$ hypernuclei with Ge detectors. The $$^4$$He target spectrum exhibited a $$gamma$$-ray peak of $$^4_{Lambda}{rm He}(1^+to 0^+)$$ at $$1.406 pm 0.002 pm 0.002$$ MeV. Compared with the energy ($$1.09 pm 0.02$$ MeV) of the corresponding transition for the mirror hypernucleus, $$^4_{Lambda}{rm H}(1^+to 0^+)$$, 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 $$^{19}$$F target run, a preliminary spectrum shows several $$gamma$$-ray peaks assigned to $$^{19}_{Lambda}{rm F}$$ transitions. Future plans of $$gamma$$-ray spectroscopy are also discussed.



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