Abstract submitted to the
         International Europhysics Conference on High Energy Physics
                  July 12 - 18, 2001, Budapest, Hungary
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       Measurement of open beauty production in photoproduction at HERA

                    
                               ZEUS Collaboration



                                    Abstract


        The production and semi-leptonic decay of heavy quarks have been 
        studied in the photoproduction process 
        e^+p -> e^+ + dijet + e^- + X with the ZEUS detector at HERA 
        using an integrated luminosity of 38.5 pb^{-1}. Events with 
        photon-proton centre-of-mass energies, W_{gamma-p}, between 134 and 
        269 GeV and a photon virtuality, Q^2, less than 1 GeV^2 were 
        selected requiring at least two jets of transverse energy 
        E_T^{jet1(2)} > 7(6) GeV and an electron in the final state. The 
        electrons were identified by employing the ionisation energy loss 
        measurement. The contribution of beauty quarks was determined using 
        the transverse momentum of the electron relative to the axis of the 
        closest jet, p_T^{rel}. The data, after background subtraction, 
        were fit with a Monte Carlo simulation including beauty and charm 
        decays. The measured beauty cross section was extrapolated to the 
        parton level with the b quark restricted to the region of 
        transverse momentum p_T^{b} > p_T^{min} = 5 GeV and pseudorapidity 
        |eta^{b}| < 2. The extrapolated cross section is 
        1.6 \pm 0.4 (stat.)^{+0.3}_{-0.5} (syst.) ^{+0.2}_{-0.4} (ext.) nb. 
        The result is compared to a perturbative QCD calculation performed 
        to next-to-leading order.