Measurement of D* photoproduction at three different centre-of-mass energies at HERA

TL;DR

This study measures D* meson production at three different energies at HERA, analyzing how the production rate varies with energy and comparing results to QCD predictions, thus testing the theory's accuracy.

Contribution

It provides the first detailed measurement of D* photoproduction at multiple energies at HERA, normalizing results to reduce systematic uncertainties and testing NLO QCD predictions.

Findings

QCD predictions match the energy dependence of D* production well.

Normalization to the highest energy data cancels systematic effects.

Results support the validity of NLO QCD in describing photoproduction.

Abstract

The photoproduction of $D^{*\pm}$ mesons has been measured with the ZEUS detector at HERA at three different ep centre-of-mass energies, $\sqrt{s}$, of 318, 251 and 225 GeV. For each data set, $D^*$ mesons were required to have transverse momentum, $p_T^{D^*}$, and pseudorapidity, $\eta^{D^*}$, in the ranges $1.9 < p_T^{D^*} < 20$ GeV and $|\eta^{D^*}|<1.6$. The events were required to have a virtuality of the incoming photon, $Q^2$, of less than 1 GeV$^2$. The dependence on $\sqrt{s}$ was studied by normalising to the high-statistics measurement at $\sqrt{s} =318$ GeV. This led to the cancellation of a number of systematic effects both in data and theory. Predictions from next-to-leading-order QCD describe the $\sqrt{s}$ dependence of the data well.