Three- and four-jet final states in photoproduction at HERA

TL;DR

This paper reports the first measurement of four-jet photoproduction cross sections at HERA, comparing experimental results with Monte Carlo models and perturbative QCD calculations to enhance understanding of multi-jet processes.

Contribution

It presents the first measurement of four-jet photoproduction cross sections at HERA and compares these with theoretical models and calculations.

Findings

Four-jet cross section measured for the first time.

Three- and four-jet cross sections agree with Monte Carlo models.

Perturbative QCD calculations describe three-jet data well.

Abstract

Three- and four-jet final states have been measured in photoproduction at HERA using the ZEUS detector with an integrated luminosity of 121 pb^-1. The results are presented for jets with transverse energy E_T^jet>6 GeV and pseudorapidity |eta^jet|<2.4, in the kinematic region given by the virtuality of the photon Q^2<1 GeV^2 and the inelasticity 0.2<y<0.85 and in two mass regions defined as 25<M_nj<50 GeV and M_nj>50 GeV, where M_nj is the invariant mass of the n-jet system. The four-jet photoproduction cross section has been measured for the first time and represents the highest-order process studied at HERA. Both the three- and four-jet cross sections have been compared with leading-logarithmic parton-shower Monte Carlo models, with and without multi-parton interactions. The three-jet cross sections have been compared to an order(alpha alpha_s^2) perturbative QCD calculation.