Measurement of Elastic $\phi$ Photoproduction at HERA

TL;DR

This paper measures the elastic photoproduction of phi mesons at HERA, analyzing cross sections, angular distributions, and energy dependence to understand the underlying diffractive processes.

Contribution

It provides the first detailed measurement of differential and integrated phi photoproduction cross sections at HERA energies, confirming the soft diffractive nature of the process.

Findings

Exponential shape of differential cross section $d\sigma/dt$

Weak energy dependence of cross section and slope parameter

Consistency with s-channel helicity conservation

Abstract

The production of $\phi$ mesons in the reaction $e^{+}p \rightarrow e^{+} \phi p$ ($\phi \rightarrow K^{+}K^{-}$) at a median $Q^{2}$ of $10^{-4} \ \rm{GeV^2}$ 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 $0.1<|t|<0.5 \ \rm{GeV^2}$ and $60 < W < 80 \ \rm{GeV}$. An integrated cross section of $\sigma_{\gamma p \rightarrow \phi p} = 0.96 \pm 0.19^{+0.21}_{-0.18}$ $\rm{\mu b}$ has been obtained by extrapolating to {\it t} = 0. When compared to lower energy data, the results show a weak energy dependence of both $\sigma_{\gamma p \rightarrow \phi p}$ 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.