Measurement of inclusive D*+- and associated dijet cross sections in photoproduction at HERA

TL;DR

This paper measures inclusive D*+- meson and dijet production cross sections in photoproduction at HERA, comparing results with NLO QCD predictions, revealing discrepancies especially in the forward direction and highlighting the role of resolved photon processes.

Contribution

It provides the first detailed measurement of D*+- and associated dijet cross sections in photoproduction at HERA, including comparisons with NLO QCD models and insights into photon structure.

Findings

Measured cross sections are generally above NLO predictions.

Significant resolved photon contribution from charm in the photon.

Discrepancies observed in the forward (proton) direction.

Abstract

Inclusive photoproduction of D*+- mesons has been measured for photon-proton centre-of-mass energies in the range 130 < W < 280 GeV and a photon virtuality Q^2 < 1 GeV^2. The data sample used corresponds to an integrated luminosity of 37 pb^-1. Total and differential cross sections as functions of the D* transverse momentum and pseudorapidity are presented in restricted kinematical regions and the data are compared with next-to-leading order (NLO) perturbative QCD calculations using the "massive charm" and "massless charm" schemes. The measured cross sections are generally above the NLO calculations, in particular in the forward (proton) direction. The large data sample also allows the study of dijet production associated with charm. A significant resolved as well as a direct photon component contribute to the cross section. Leading order QCD Monte Carlo calculations indicate that the resolved contribution arises from a significant charm component in the photon. A massive charm NLO parton level calculation yields lower cross sections compared to the measured results in a kinematic region where the resolved photon contribution is significant.