Search for signals of bound (K)over-bar nuclear states in antiproton-He-4 annihilations at rest

摘要

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. (c) 2007 Elsevier B.V. All rights reserved.