Search for Resonances Decaying to e^+ jet in e^+ p Interactions at HERA

TL;DR

This study analyzes the e^+ jet invariant mass spectrum at HERA, finding no conclusive evidence for new resonances but setting limits on leptoquark and squark production at high masses.

Contribution

First search for resonances decaying to e^+ jet in e^+ p interactions at HERA, providing limits on leptoquark and squark production for various masses.

Findings

No significant excess observed above 210 GeV

Limits set on leptoquark and squark production cross sections

Specific leptoquark types excluded at 95% confidence for certain masses

Abstract

The e^+ jet invariant mass spectrum produced in the reaction e^+ p -> e^+ X has been studied at a center-of-mass energy of 300 GeV. The data were collected using the ZEUS detector operating at the HERA collider, and correspond to an integrated luminosity of 47.7 pb^{-1}. The observed mass spectrum is in good agreement with Standard Model expectations up to an e^+ jet mass of 210 GeV. Above this mass, some excess is seen. The angular distribution of these events is typical of high-Q^2 neutral current events and does not give convincing evidence for the presence of a narrow scalar or vector state. Limits are presented on the product of cross section and branching ratio for such a state and are interpreted as limits on leptoquark or R-parity-violating squark production. Specific leptoquark types are ruled out at 95% confidence level for coupling strength lambda=0.3 for masses between 150 and 280 GeV.