Scale Influence on the Energy Dependence of Photon-Proton Cross Sections

TL;DR

This study investigates how the energy dependence of photon-proton cross sections varies with the scale, defined by transverse momentum, revealing a steep increase in the W dependence slope with higher transverse momentum, and compares it with Q^2 evolution.

Contribution

It provides new insights into the scale dependence of photon-proton interactions at low Q^2, linking transverse momentum to the energy dependence of cross sections.

Findings

W dependence slope increases with transverse momentum

Comparison with Q^2 evolution shows consistent trends

Results support QCD and Regge phenomenology interpretations

Abstract

The scale dependence of the evolution of photoproduction cross sections with the photon-proton centre of mass energy W is studied using low Q^2 < 0.01 GeV^2 e^+p interactions collected by the H1 experiment at HERA. The value of the largest transverse momentum of a charged particle in the photon fragmentation region is used to define the hard scale. The slope of the $W$ dependence of the cross section is observed to increase steeply with increasing transverse momentum. The result is compared to measurements of the Q^2 evolution of the W dependence of the virtual photon-proton cross section. Interpretations in terms of QCD and in terms of Regge phenomenology are discussed.