Evidence for a narrow baryonic state decaying to K0s-p and K0s-pbar in deep inelastic scattering at HERA

TL;DR

This paper reports evidence for a narrow baryonic state decaying to K0s-p and K0s-pbar observed in deep inelastic scattering at HERA, supporting the existence of a pentaquark with a mass around 1522 MeV.

Contribution

It provides experimental evidence for a narrow baryonic resonance consistent with a pentaquark in deep inelastic scattering data, extending previous fixed-target results.

Findings

Evidence for a resonance at 1522 MeV with a width consistent with experimental resolution.

Signal observed at high Q2 with over 220 events in the specified mass range.

Background fluctuation probability below 6x10^{-5}.

Abstract

A resonance search has been made in the K0s p and K0s pbar invariant-mass spectrum measured with the ZEUS detector at HERA using an integrated luminosity of 121 pb-1. The search was performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318 GeV for exchanged photon virtuality, Q2, above 1 GeV2. Recent results from fixed-target experiments give evidence for a narrow baryon resonance decaying to K+ n and K0s p, interpreted as a pentaquark. The results presented here support the existence of such state, with a mass of 1521.5+/-1.5(stat.)^{+2.8}_{-1.7}(syst.) MeV and a Gaussian width consistent with the experimental resolution of 2 MeV. The signal is visible at high Q2 and, for Q2>20 GeV2, contains 221+/-48 events. The probability of a similar signal anywhere in the range 1500-1560 MeV arising from fluctuations of the background is below 6x10^{-5}.