The first measurement of inclusive D-s(+/-) photoproduction at HERA has bee
n performed with the ZEUS detector for photon-proton centre-of-mass energie
s; 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 th
e uncertainty in the D-s(+/-) decay branching ratio. The measurements are c
ompared with inclusive D*(+/-) photoproduction cross sections in the same k
inematic 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 t
he ZEUS D* (+/-) cross sections. The ratio of D-s(+/-) to D*(+/-) cross sec
tions is 0.41 +/- 0.07(stat.)(-0.05)(+0.03)(syst.) +/- 0.10 (br.). From thi
s ratio, the strangeness-suppression factor in charm photoproduction, withi
n 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 go
od agreement with those obtained in charm production in e(+)e(-) annihilati
on. (C) 2000 Elsevier Science B.V. All rights reserved.