Dijet angular distributions in photoproduction of charm at HERA

TL;DR

This paper measures dijet angular distributions in charm photoproduction at HERA, providing insights into the photon’s charm content through comparison with theoretical models.

Contribution

It presents the first detailed measurement of angular distributions in charm dijet photoproduction, distinguishing direct and resolved photon processes.

Findings

Angular distributions indicate charm from the photon.

Results agree with NLO QCD predictions.

Evidence supports photon-originated charm production.

Abstract

Dijet angular distributions of photoproduction events in which a $D^{*\pm}$ meson is produced in association with one of two energetic jets have been measured with the ZEUS detector at HERA, using an integrated luminosity of 120 pb$^{-1}$. Differential cross sections as a function of the angle between the charm-jet and the proton-beam direction in the dijet rest frame have been measured for samples enriched in direct or resolved photon events. The results are compared with predictions from leading-order parton-shower Monte Carlo models and with next-to-leading-order QCD calculations. The angular distributions show clear evidence for the existence of charm originating from the photon.