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

Abstract

The photoproduction of $D^{\ast \pm }$ 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, $D^{\ast }$ mesons were required to have transverse momentum, $p_T^{D^{\ast }}$, and pseudorapidity, $\hat{I}{\cdot }^{D^{\ast }}$, in the ranges $1.9<p_T^{D^{\ast }}<20$ GeV and $|\hat{I}{\cdot }^{D^{\ast }}|<1.6$. 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.

17 pages, 7 figures, accepted by JHEP. Updated version includes comments from journal referee