Evidence for the Strangeness S=+1 Pentaquark from LEPS and CLAS Experiments

Abstract

There are now several experimental collaborations that have seen evidence for a narrow state in the mass spectrum of the ($nK^+$) system. Two of these experiments, from the LEPS collaboration in Japan and the CLAS collaboration in the USA, are described briefly. Both use similar photoproduction reactions with a $K^+K^-$ pair in the final state. In addition, data from the CLAS collaboration for the $\gamma p \to K_s K^+ n$ reaction are presented for the first time, which has no prominant peak in the ($nK^+$) mass spectrum when the $K_s$ angle is limited to forward angles.