“Kpp”, a K-Meson nuclear bound state, observed in 3He(K, Λp)n Reactions

J-PARC E15 Collaboration

Research output: Contribution to journalArticlepeer-review


We observed a distinct peak in the Λp invariant mass spectrum of 3He(K, Λp)n, well below the mass threshold of mK + 2mp. 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 → ΛN. We found that the simplest fit to the observed peak gives us a Breit-Wigner pole position at BKpp = 47 ± 3 (stat.) +36 (sys.) MeV having a width ΓKpp = 115 ± 7 (stat.) +1020 (sys.) MeV, and the S-wave Gaussian reaction form-factor parameter QKpp = 381 ± 14 (stat.) +570 (sys.) MeV/c, as a new form of the nuclear bound system with strangeness - “Kpp”.

Original languageEnglish
JournalUnknown Journal
Publication statusPublished - 2018 May 30


  • Kaon
  • Mesonic nuclear bound state
  • Strangeness

ASJC Scopus subject areas

  • General

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