Charged Particle Cross Sections in Photoproduction and Extraction of the Gluon Density in the Photon

TL;DR

This paper uses photoproduction data from HERA to measure charged particle cross-sections and extract the gluon density in the photon, revealing a rise in gluon content at lower x_gamma values.

Contribution

It introduces a new method to determine the gluon density in the photon using high pT charged particles and perturbative QCD analysis.

Findings

Gluon content of the photon increases at lower x_gamma.

Measured cross-sections are sensitive to photon parton densities.

New method effectively extracts gluon distribution in the photon.

Abstract

Photoproduction data collected with the H1 detector at HERA in 1994 are used to study the cross-sections for inclusive charged particle production and the structure of the photon. The differential cross-sections dsigma/dpT2, for |eta| < 1 in the HERA laboratory frame, and dsigma/deta for pT > 2 GeV/c and pT > 3 GeV/c have been measured. Model calculations of these cross-sections, based on perturbative QCD, indicate that the results are sensitive to the parton densities of the photon as well as to higher order effects, which are phenomenologically treated by multiple interactions. This sensitivity is exploited to determine the leading order x_gamma distribution of partons in the photon using a new method based on high pT charged particles. The gluon content of the photon is extracted and found to rise with decreasing x_gamma.