Elastic Photoproduction of ${\rho }^0$ Mesons at HERA

Abstract

The cross section for the elastic photoproduction of \r0 mesons ($\gamma p\to {\rho }^{0}p$) has been measured with the H1 detector at HERA for two average photon-proton centre-of-mass energies of 55 and 187 GeV. TheFcenterline lower energy point was measured by observing directly the ${\rho }^0$ decay giving a cross section of $9.1\pm 0.9 (\stat)\pm 2.5 (\syst) μ$b. The logarithmic slope parameter of the differential cross section, $\mathrm{d}\sigma /\mathrm{d}t$, is found to be $10.9 \pm 2.4 (\stat) \pm 1.1 (\syst) $GeV${}^{-2}$. The \r0 decay polar angular distribution is found to be consistent with s-channel helicity conservation. The higher energy cross section was determined from analysis of the lower part of the hadronic invariant mass spectrum of diffractive photoproduction and found to be $13.6\pm 0.8 (\stat)\pm 2.4 (\syst) μ$b.

25 pages, latex, 9 Figures appended as uuencoded file