Measurement of the photon-proton total cross section at a center-of-mass energy of 209 GeV at HERA

TL;DR

This paper reports a precise measurement of the photon-proton total cross section at 209 GeV center-of-mass energy at HERA, confirming its energy dependence aligns with existing high-energy hadron collision models.

Contribution

It provides the first dedicated measurement of the photon-proton total cross section at this energy with controlled systematic uncertainties.

Findings

Total cross section measured as 174 ± 1 (stat.) ± 13 (syst.) microbarns.

Energy dependence consistent with high-energy p-p and p-pbar data.

Measurement supports existing parameterizations of high-energy photon-proton interactions.

Abstract

The photon-proton total cross section has been measured in the process e+ p -> e+ gamma p -> e+ X with the ZEUS detector at HERA. Events were collected with photon virtuality Q^2 < 0.02 GeV^2 and average gamma-p center-of-mass energy W_{gamma p} = 209 GeV in a dedicated run, designed to control systematic effects, with an integrated luminosity of 49 nb^{-1}. The measured total cross section is sigma_{tot}^{gamma p} = 174 +- 1 (stat.) +- 13 (syst.) microbarns. The energy dependence of the cross section is compatible with parameterizations of high-energy p-p and p-pbar data.