Measurement Of Elastic Phi Photoproduction At Hera

The production of phi mesons in the reaction e(+)p --> e(+)phi p (phi --> K+K-) at a median Q(2) of 10(-4) GeV2 has been studied with the ZEUS detector at HERA. The differential phi photoproduction cross section d sigma/dt has an exponential shape and has been determined in the kinematic range 0.1 < \t\ < 0.5 GeV2 and 60 < W < 80 GeV. An integrated cross section of sigma(gamma p-->phi p) = 0.96+/-0.19(-0.18)(+0.21) mu b has been obtained by extrapolating to t = 0. When compared to lower energy data, the results show a weak energy dependence of both sigma(gamma-->phi p) and the slope of the t distribution. The phi decay angular distributions are consistent with s-channel helicity conservation. From lower energies to HERA energies, the features of phi photoproduction are compatible with those of a soft diffractive process.