Measurement of inclusive (Ds±) photoproduction at HERA

The first measurement of inclusive Ds± photoproduction at HERA has been performed with the ZEUS detector for photon-proton centre-of-mass energies 130<W<280 GeV. The measured cross section for 3<ρ (perpendicular) Ds<12 GeV and |ηDs| < 1.5 is σep#yields#D#sub s#x=3.79±0.59(stat.)+0.26-0.46(syst.)±0.94 (br.) nb, where the last error arises from the uncertainty in the Ds± decay branching ratio. The measurements are compared with inclusive D*± photoproduction cross sections in the same kinematic region and with QCD calculations. The Ds± cross sections lie above a fixed-order next-to-leading order calculation and agree better with a tree-level Ο(ααs3) calculation that was tuned to describe the ZEUS D*± cross sections. The ratio of Ds± to D*± cross sections is 0.41±0.07 (stat.)0.030.05(syst.)±0.10 (br.). From this ratio, the strangeness-suppression factor in charm photoproduction, within the LUND string fragmentation model, has been calculated to be γs=0.27±0.05±0.07 (br.). The cross-section ratio and γs are in good agreement with those obtained in charm production in e+e- annihilation.