Measurement of D* Meson Cross Sections at HERA and Determination of the Gluon Density in the Proton using NLO QCD

TL;DR

This paper measures D* meson production cross sections at HERA in different regimes and uses NLO QCD calculations to extract the gluon density in the proton, confirming previous results from structure function analyses.

Contribution

It provides new measurements of D* meson cross sections and determines the gluon distribution in the proton using NLO QCD, extending the kinematic range of previous studies.

Findings

NLO QCD describes the differential cross sections well.

Gluon distribution x_g g(x_g) is extracted in the range 7.5x10^{-4} to 4x10^{-2}.

Results agree with gluon distributions from F_2 scaling violations.

Abstract

With the H1 detector at the ep collider HERA, D* meson production cross sections have been measured in deep inelastic scattering with four-momentum transfers Q^2>2 GeV2 and in photoproduction at energies around W(gamma p)~ 88 GeV and 194 GeV. Next-to-Leading Order QCD calculations are found to describe the differential cross sections within theoretical and experimental uncertainties. Using these calculations, the NLO gluon momentum distribution in the proton, x_g g(x_g), has been extracted in the momentum fraction range 7.5x10^{-4}< x_g <4x10^{-2} at average scales mu^2 =25 to 50 GeV2. The gluon momentum fraction x_g has been obtained from the measured kinematics of the scattered electron and the D* meson in the final state. The results compare well with the gluon distribution obtained from the analysis of scaling violations of the proton structure function F_2.