Measurement of [formula omitted] meson cross sections at HERA and determination of the gluon density in the proton using NLO QCD

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 > 3 GeV 2 and in photoproduction at energies around W γp ≈ 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 7.5 × 10 −4 < x g < 4 × 10 −2 at average scales μ 2 = 25 to 50 GeV 2. 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.