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

TL;DR

This paper reports evidence for an exotic baryon, Theta+(1540), observed in photoproduction reactions from protons and deuterons, supporting its existence predicted by the chiral soliton model.

Contribution

It provides experimental evidence for the Theta+(1540) baryon in photoproduction reactions, confirming prior observations and supporting theoretical predictions.

Findings

Evidence for Theta+(1540) in neutron-kaon invariant mass

Consistent results with previous LEPS and ITEP experiments

Observation in both deuteron and proton target data

Abstract

CLAS photoproduction data on deuterium and hydrogen targets have been analyzed in a search for an exotic baryon state with strangeness S=+1, the \Theta^+ (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 gamma d --> 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 gamma p --> pi^+K^-K^+n was studied. Evidence for the \Theta^+ state is found in both analyses 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.