Evidence for a narrow resonance at 1530 MeV/c2 in the K0 p - system of the reaction pp --> Sigma+ K0 p from the COSY-TOF experiment

TL;DR

This paper reports the observation of a narrow resonance at 1530 MeV/c2 in the K0 p system from the pp --> Sigma+ K0 p reaction, providing evidence for the Theta+ pentaquark state with strangeness S=+1.

Contribution

First experimental evidence of a narrow resonance at 1530 MeV/c2 in the K0 p system in proton-proton collisions, supporting the existence of the Theta+ pentaquark.

Findings

Narrow peak observed at 1530 MeV/c2 with 4-6 sigma significance

Resonance width estimated to be less than 18 MeV/c2 (FWHM)

Estimated cross section around 0.4 microbarns

Abstract

The hadronic reaction pp --> Sigma+ K0 p was measured exclusively at a beam momentum of 2.95 GeV/c using the TOF detector at the COSY storage ring. A narrow peak was observed in the invariant mass spectrum of the K0 p subsystem at 1530 +- 5 MeV/c2 with a significance of 4 - 6 standard deviations, depending on background assumptions. The upper limit of 18 +- 4 MeV/c2 (FWHM) for its width is given by the experimental resolution. The corresponding total cross section is estimated to be about 0.4 +- 0.1(stat) +- 0.1(syst) microbarn. Since a resonance in this subsystem must have strangeness S = + 1 we claim it to be the Theta+ state for which very recently evidence was found in various experiments.