Abstract submitted to the
         International Europhysics Conference on High Energy Physics
                  July 12 - 18, 2001, Budapest, Hungary
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         Study of the effective transverse momentum of partons in the 
             proton using prompt photons in photoproduction at HERA

                    
                               ZEUS Collaboration



                                    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 \pm 0.18 ^{+0.18}_{-0.20} GeV for the gamma-p 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.