Recent Spectroscopy Results from ZEUS

TL;DR

This paper reports evidence for a narrow baryonic state consistent with the pentaquark theta^+ and its antiparticle, based on recent ZEUS detector data from deep inelastic scattering at HERA.

Contribution

It provides the first evidence for the antiparticle of the pentaquark theta^+ in high-energy ep collisions.

Findings

Evidence for a narrow resonance at 1521.5 MeV in Ks p and Ks pbar spectra.

First experimental indication of the antiparticle of the pentaquark theta^+.

Resonance width consistent with experimental resolution.

Abstract

Recent results on light hadron spectroscopy are reported, with special emphasis on the evidence for a narrow baryonic state decaying to Ks p and Ks pbar, compatible with the pentaquark state theta^+ observed by fixed target experiments. The data were collected with the ZEUS detector at HERA using an integrated luminosity of 121 pb^-1. The analyses were performed in the central rapidity region of inclusive deep inelastic scattering at an ep centre-of-mass energy of 300-318 GeV. Evidence for a narrow resonance in the Ks p and Ks pbar invariant mass spectrum is obtained, with mass 1521.5 \pm 1.5(stat)^{+2.8}_{-1.7}(syst) and width consistent with the experimental resolution. If the Ks p part of the signal is identified with the strange pentaquark theta^+, the Ks pbar part is the first evidence for its antiparticle, thetabar^-. Supporting results on other light hadron resonances are also discussed.