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

The cross sections for the photoproduction of D*± mesons have been measured with the ZEUS detector at HERA at three different ep centre-of-mass energies, √(s), of 318, 251 and 225 GeV. For each data set, D*± mesons were required to have transverse momentum, pD*T, and pseudorapidity, ηD*, in the ranges 1.9<pD*T<20 GeV and vertical stroke ηD* vertical stroke <1.6. The events were required to have a virtuality of the incoming photon, Q2, of less than 1 GeV2. The dependence on √(s) was studied by normalising to the high-statistics measurement at √(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 √(s) dependence of the data well.