Evidence for an Exotic Baryon State, Θ+(1540), in Photoproduction Reactions from Protons and Deuterons with CLAS

CLAS photoproduction data on deuterium and hydrogen targets have been analyzed in a search for an exotic baryon state with strangeness S = +1, the Θ+ (originally named the Z+). This resonance was predicted recently in theoretical work based on the chiral soliton model as a lowest mass member of an anti‐decuplet of 5‐quark states. The reaction γd → pK−K+n, which requires a final state interaction inside the deuteron, was used in the analysis of deuteron data. In the analysis of proton data, the reaction γp → π+K−K+n was studied. Evidence for the Θ+ state is found in both analyzes in the invariant mass distribution of the nK+. Our results are consistent with previously reported results by LEPS/Spring‐8 collaboration (Japan), and by the ITEP (Moscow) group.