Measurement of Three-jet Distributions in Photoproduction at HERA

TL;DR

This paper reports measurements of three-jet production in photoproduction at HERA, showing that angular distributions align with QCD models and reveal effects like initial state radiation and color coherence.

Contribution

First measurement of three-jet distributions in photoproduction at HERA, testing QCD predictions and parton shower models against experimental data.

Findings

Angular distributions deviate from uniform phase space

Data agree with parton shower and pQCD models

Evidence of initial state radiation and color coherence effects

Abstract

The cross section for the photoproduction of events containing three jets with a three-jet invariant mass of M_3J > 50 GeV has been measured with the ZEUS detector at HERA. The three-jet angular distributions are inconsistent with a uniform population of the available phase space but are well described by parton shower models and O(alpha alpha_s^2) pQCD calculations. Comparisons with the parton shower model indicate a strong contribution from initial state radiation as well as a sensitivity to the effects of colour coherence.