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

TL;DR

This paper reports measurements of elastic  photoproduction cross sections at two energies at HERA, analyzing the differential cross section and decay angular distributions to understand the underlying physics.

Contribution

It provides new measurements of  photoproduction cross sections at 55 and 187 GeV, including the slope parameter and decay angular distributions, advancing understanding of vector meson production.

Findings

Cross section at 55 GeV: 9.1  0.9 (stat)  2.5 (syst) 

Differential cross section slope: 10.9  2.4 (stat)  1.1 (syst) GeV

Cross section at 187 GeV: 13.6  0.8 (stat)  2.4 (syst) 

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 $9.1\pm 0.9 (\stat)\pm 2.5 (\syst) \mu$b. The logarithmic slope parameter of the differential cross section, ${\rm d}\sigma/{\rm d}t$, 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 $13.6\pm 0.8 (\stat)\pm 2.4 (\syst) \mu$b.