J-PARC E15 collaborationAjimura, S.Asano, H.Beer, G.Berucci, C.Bhang, H.Bragadireanu, M.Buehler, P.Busso, L.et al.2019-03-272019-03-2720192019Ajimura, S., Asano, H., Beer, G., Berucci, C., Bhang, H., Bhang, H. & Zmeskal, J. (2018). “K−pp”, a K-meson nuclear bound state, observed in 3He(K−, Λ p)n reactions. Physics Letters B, (789), 620-625. https://doi.org/10.1016/j.physletb.2018.12.058https://doi.org/10.1016/j.physletb.2018.12.058http://hdl.handle.net/1828/10675We observed a distinct peak in the Ap invariant mass spectrum of 3 He(K −, Ap)n, well below mK 2mp , i.e., the mass threshold of the K − to be bound to two protons. By selecting a relatively large momentum- transfer region q = 350 ∼ 650 MeV/c, one can kinematically separate the peak from the quasi-free process, KN → KN followed by the non-resonant absorption by the two spectator-nucleons KNN → AN. We found that the simplest fit to the observed peak gives us a Breit–Wigner pole position at BKpp = 47 ± 3 (stat.) +3 (sys.) MeV having a width rKpp = 115 ± 7 (stat.) +10 (sys.) MeV, and the S-wave Gaussian reaction form-factor parameter QKpp 381 14 (stat.) 0 (sys.) MeV/c, as a new form of the nuclear bound system with strangeness – “K − pp”.enKaonStrangenessMesonic nuclear bound stateArticleDepartment of Physics and Astronomy