Exotic State Searches at the SPring-8: Observation of a Pentaquark State Theta^+ Baryon

TL;DR

This paper reports the observation of a narrow exotic baryon resonance, the Theta^+ pentaquark, at 1.54 GeV, providing experimental evidence for a state predicted by the chiral soliton model.

Contribution

First observation of a pentaquark state with strangeness S=+1, supporting the existence of exotic baryons beyond three-quark models.

Findings

Resonance peak at 1.54 GeV with a width less than 0.025 GeV

Significance level of 4.6 sigma for the resonance

Consistent with predictions of the antidecuplet baryon from the chiral soliton model

Abstract

A narrow resonance peak was observed at 1.54 +/- 0.01 GeV as an exotic baryon with strangeness S = +1 in the gamma + n going to K^+ + K^- + n reaction on Carbon. The new state have a width smaller than 0.025 GeV and a Gaussian significance of 4.6 sigma. It can not be interpreted as three quark state and is consistent with the lightest member of an antidecuplet of baryons predicted by the chiral soliton model.