Eur. Phys. J. C (2004) 34: 255-265
https://doi.org/10.1140/epjc/s2004-01735-3

experimental physics

Search for QCD-instanton induced events in deep inelastic ep scattering at HERA

Abstract

A search for QCD-instanton-induced events in deep inelastic ep scattering has been performed with the ZEUS detector at the HERA collider, using data corresponding to an integrated luminosity of 38 pb^-1. A kinematic range defined by cuts on the photon virtuality, Q ² > 120 GeV², and on the Bjorken scaling variable, x > 10^-3, has been investigated. The QCD-instanton induced events were modelled by the Monte Carlo generator QCDINS. A background-independent, conservative 95% confidence level upper limit for the instanton cross section of 26 pb is obtained, to be compared with the theoretically expected value of 8.9 pb.