An Event excess observed in the deeply bound region of the C missing-mass spectrum

Ichikawa, Yudai*   ; Fujita, Manami; Hasegawa, Shoichi   ; Hayakawa, Shuhei; Sako, Hiroyuki   ; Sato, Susumu  ; Tamura, Hirokazu; Tanida, Kiyoshi   ; Yamamoto, Takeshi  ; 36 of others*

We have measured, for the first time, the inclusive missing-mass spectrum of the C reaction at an incident kaon momentum of 1.8 GeV/c at the J-PARCK 1.8 beamline. We observed a prominent quasi-elastic peak ( in this spectrum. In the quasi-elastic peak region, the effect of secondary interaction is apparently observed as a peak shift, and the peak exhibits a tail in the bound region. We compared the spectrum with a theoretical calculation based on the Green's function method by assuming different values of the parameters for the -nucleus optical potential. We found that the spectrum shape in the binding-energy region -300 MeV 40 MeV is best reproduced with the potential depths = -80 MeV (real part) and = -40 MeV(imaginary part). On the other hand, we observed a significant event excess in the deeply bound region around 100 MeV, where the major decay channel of is energetically closed, and the non-mesonic decay modes ( and ) should mainly contribute. The enhancement is fitted well by a Breit-Wigner function with a kaon-binding energy of 90 MeV and width 100 MeV. A possible interpretation is a deeply bound state of a -nucleus system.