Measurement of D*+/- diffractive cross sections in photoproduction at HERA

The first measurement of D*+/- meson diffractive photoproduction cross sections has been performed with the ZEUS detector at the HERA $ep$ collider, using an integrated luminosity of 38 pb^-1. The measurement has been performed for photon--proton center-of-mass energies in the range 130 < W < 280 GeV and photon virtualities Q^2 < 1 GeV^2. D*+/- mesons have been reconstructed with p_T(D*)>2 GeV and -1.5 D^0 \pi^+_s with D^0 --> K-\pi^+ (+c.c.). The diffractive component has been selected with 0.001<x_Pom<0.018. The measured diffractive cross section in this kinematic range is: \sigma_(ep --> e'D*Xp') = 0.74 +/- 0.21 (stat.)^{+0.27}_{-0.18} (syst.) +/-0.16 (p. diss.) ~nb (ZEUS preliminary). Measured integrated and differential cross sections have been compared to theoretical expectations.Comment: LaTeX2e, 10 pages, 6 Postscript figures. Talk given at the Russian Academy of Science (RAS) Nuclear Physics 2000 Conference, Moscow, Russia, November 27-December 2, 2000. To be published in Rus. Nucl. Phys. (Ya.F.), Proceedings of RAS Nucl. Phys. 2000 Con