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

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(-0.20)(+0.18) GeV for the gammap 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. (C) 2001 Elsevier Science B.V. All rights reserved.