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 st HERA using an integrated luminosity of 38.5 pb(-1). Events wit
h photon-proton centre-of-mass energies, W-gammap, between 134 and 289 GeV
and a photon virtuality, Q(2), less than 1 GeV2 were selected requiring at
least two jets of transverse energy E-T(jet(2)) > 7(6) GeV and an electron
in the final state. The electrons were identified by employing the ionisati
on energy loss measurement. The contribution of beauty quarks was determine
d using the transverse momentum of the electron relative to the axis of the
closest jet, p(T)(rol). The data, after background subtraction, were fit w
ith a Monte Carlo simulation including beauty and charm decays, The measure
d beauty cross section was extrapolated to the parton level with the b quar
k restricted to the region of tranverse momentum p(T)(b) > p(T)(min) = 5 Ge
V and pseudorapidity \ eta (b)\ < 2 The extrapolated cross section is 1.6 /- 0.4 (stat.)(-0.5)(+0.3), (syst.)(-0.4)(+0.2) (ext.) nb. The result is co
mpared to a perturbative QCD calculation performed to next-to-leading order
.