Limits for the central production of Theta^+ and Xi^{--} pentaquarks in 920 GeV pA collisions

TL;DR

This study searched for pentaquark particles Theta^+ and Xi^{--} in high-energy proton-nucleus collisions but found no evidence, setting upper limits on their production rates that challenge some previous claims.

Contribution

The paper provides the first stringent upper limits on the production cross sections of Theta^+ and Xi^{--} pentaquarks in proton-induced reactions at 41.6 GeV, challenging earlier positive signals.

Findings

No evidence for Theta^+ or Xi^{--} signals was observed.

Upper limits on production cross sections are significantly below some model predictions.

Results contradict previous experimental claims of Xi^{--} detection.

Abstract

We have searched for Theta^+(1540) and Xi^{--}(1862) pentaquark candidates in proton-induced reactions on C, Ti and W targets at mid-rapidity and \sqrt{s} = 41.6 GeV. In 2x10^8 inelastic events we find no evidence for narrow (sigma~5 MeV) signals in the Theta^+ -> pK_s and Xi^{--} -> Xi^-pi^- channels; our 95% CL upper limits (UL) for the inclusive production cross section times branching fraction Bx(dsigma/dy)|_{y~0} are 3.7 and 2.5 microb/N. The UL of the yield ratio of [Theta^+ / Lambda(1520)] < 2.7% is significantly lower than model predictions. Our UL of [BxXi^{--} / Xi(1530)^0] < 4% is at variance with the results that have provided first evidence for the Xi^{--} signal.