Measurement of Elastic $\varphi$ Photoproduction at HERA

Abstract

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

23 pages, including 6 post script figures