Measurement of inclusive (Ds±) photoproduction at HERA

The first measurement of inclusive D(s)(+/-) 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 < p(perpendicular to)(Ds) < 12 GeV and \eta(Ds)\ < 1.5 is sigma(ep-->DsX) = 3.79 +/- 0.59(stat.)(-0.46)(+0.26)(syst.) +/- 0.94(br.) nb, where the last error arises from the uncertainty in the D(s)(+/-) decay branching ratio. The measurements are compared with inclusive D*(+/-) photoproduction cross sections in the same kinematic region and with QCD calculations. The D(s)(+/-) cross sections lie above a fixed-order next-to-leading order calculation and agree better with a tree-level O(alpha alpha(s)(3)) calculation that was tuned to describe the ZEUS D* (+/-) cross sections. The ratio of D(s)(+/-) to D*(+/-) cross sections is 0.41 +/- 0.07(stat.)(-0.05)(+0.03)(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 gamma(s)= 0.27 +/- 0.05 +/- 0.07(br.). The cross-section ratio and gamma(s) are in good agreement with those obtained in charm production in e(+)e(-) annihilation.