Search for Excited Quarks in ep Collisions at HERA

TL;DR

This paper reports a search for excited quarks in electron-proton collisions at HERA, setting new limits on their production and coupling parameters, but finds no evidence of their existence.

Contribution

It provides the first comprehensive search for excited quarks at HERA, extending exclusion limits based on the full dataset and multiple decay channels.

Findings

No evidence for excited quark production was observed.

New exclusion limits were set on the production cross section and coupling ratios.

The limits extend previous bounds on excited quark models.

Abstract

A search for excited quarks is performed using the full ep data sample collected by the H1 experiment at HERA, corresponding to a total integrated luminosity of 475 pb^-1. The electroweak decays of excited quarks q* -> q gamma, q* -> q Z and q* -> q W with subsequent hadronic or leptonic decays of the W and Z bosons are considered. No evidence for first generation excited quark production is found. Mass dependent exclusion limits on q* production cross sections and on the ratio f/Lambda of the coupling to the compositeness scale are derived within gauge mediated models. These limits extend the excluded region compared to previous excited quark searches.