Abstract
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 ⊥ D s <12 GeV and | η D s |<1.5 is σ ep→D sX =3.79±0.59 (stat.) +0.26 −0.46 (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( αα 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.) +0.03 −0.05 (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 γ s=0.27±0.05±0.07 (br.) . The cross-section ratio and γ s are in good agreement with those obtained in charm production in e + e − annihilation.
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