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

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 γp centre-of-mass energy range 134 W k T 〉 to rise with interaction energy.