Study of the effective transverse momentum of partons in the proton using prompt photons in photoproduction at HERA

TL;DR

This paper measures the effective transverse momentum of partons in the proton using prompt photon photoproduction data from HERA, finding results consistent with energy-dependent trends observed in hadron-hadron collisions.

Contribution

It provides a new measurement of the proton's parton transverse momentum using prompt photons at HERA, extending understanding of parton dynamics in high-energy interactions.

Findings

Measured k_T = 1.69 GeV with uncertainties

Results agree with energy-dependent trend in hadron-hadron scattering

Supports models of parton transverse momentum increasing with energy

Abstract

The photoproduction of prompt photons, together with an accompanying jet, has been measured with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb^{-1}. A study of the effective transverse momentum, k_T, of partons in the proton, as modelled within the framework of the PYTHIA Monte Carlo, gives a value of k_T = 1.69+/-0.18 ^{+0.18}_{-0.20} GeV for the photon-proton centre-of-mass energy range 134 < W < 251 GeV. This result is in agreement with the previously observed trend in hadron-hadron scattering for k_T to rise with interaction energy.