Search for signals of bound Kbar nuclear states in antiproton-4He annihilations at rest

Lambda p and Lambda d narrow peaks in the p pi(-)p and p pi(-)d invariant mass distributions are observed in anti-proton -He-4 annihilations at rest. By considering the Lambda p peak as the signature of the two-body decay of the (K) over bar pp bound state, its mass, binding energy and decay width would be 2212.1 +/- 4.9 MeV, -160.9 +/- 4.9 MeV and < 24.4 +/- 8.0 MeV with a statistical significance of 3.7 sigma. By considering the Lambda d peak as the signature of the two-body decay of the (K) over bar ppn bound state, the same quantities should be 3190 +/- 15 MeV, -121 +/- 15 MeV and < 60 MeV with a statistical significance of 2.6 sigma. Alternative explanations are also discussed. The data were collected with the OBELIX spectrometer at the LEAR complex at CERN.