Abstract

A search for a narrow baryonic state in the $pK^0_S$ and $\bar{p}K^0_S$ system has been performed in $ep$ collisions at HERA with the ZEUS detector using an integrated luminosity of 358 pb$^{-1}$ taken in 2003-2007. The search was performed with deep inelastic scattering events at an $ep$ centre-of-mass energy of 318 GeV for exchanged photon virtuality, $Q^2$, between 20 and 100 $\rm{} GeV^{2}$. Contrary to evidence presented for such a state around 1.52 GeV in a previous ZEUS analysis using a sample of 121 pb$^{-1}$ taken in 1996-2000, no resonance peak was found in the $p(\bar{p})K^0_S$ invariant-mass distribution in the range 1.45-1.7 GeV. Upper limits on the production cross section are set.

Highlights

  • The observation of a narrow baryon resonance with a mass of≈1.53 GeV, reported first by the LEPS experiment in 2003 [1,2] in the missing-mass distribution for γ A collisions, generated considerable theoretical and experimental interest

  • A narrow baryonic resonance close to the observed mass had previously been predicted in the chiral soliton model [3] and named + with quark configuration uudds

  • This paper presents the result of a search at HERA II for a narrow resonance in the p system in the central rapidity region of high-energy ep collisions in a similar kinematic region to the previous ZEUS analysis

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Summary

Introduction

≈1.53 GeV, reported first by the LEPS experiment in 2003 [1,2] in the missing-mass distribution for γ A collisions, generated considerable theoretical and experimental interest. This paper presents the result of a search at HERA II for a narrow resonance system in the central rapidity region of high-energy ep collisions in a similar kinematic region to the previous ZEUS analysis. The sample includes both e+ p and e− p collisions at a centre-of-mass energy of 318 GeV. The analysis was done with DIS events, requiring a visible scattered electron in the detector, at a photon virtuality, Q 2, in the range 20–100 GeV2

Experimental set-up
Monte Carlo simulation
Event sample
Proton selection and particle identification
Results
Upper limits on the production cross section
Summary
Full Text
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