Measurement of charm fragmentation ratios and fractions in photoproduction at HERA

The production of D(*+), D(0), D(+), D(s)(+) and Lambda(+)(c) charm hadrons and their antiparticles in ep scattering at HERA was measured with the ZEUS detector using an integrated luminosity of 79 pb(-1). The measurement has been performed in the photoproduction regime with the exchanged-photon virtuality Q(2) < 1 GeV(2) and for photon-proton centre-of-mass energies in the range 130 < W < 300 GeV. The charm hadrons were reconstructed in the range of transverse momentum PT (D, A,) > 3.8 GeV and pseudorapidity vertical bar eta(D, Lambda(c))vertical bar < 1.6. The production cross sections were used to determine the ratio of neutral and charged D-meson production rates, R(u/d), the strangeness-suppression factor, gamma(s), and the fraction of charged D mesons produced in a vector state, P(v)(d). The measured R(u/d) and gamma(s), values agree with those obtained in deep inelastic scattering and in e(+)e(-) annihilations. The measured P(v)(d) value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron, f(c -> D, Lambda(c)), were derived in the given kinematic range. The measured open-charm fragmentation fractions are consistent with previous results, although the measured f(c -> D(*+)) is smaller and f (c -> Lambda(+)(c)) is larger than those obtained in e(+)e(-) annihilations. These results generally support the hypothesis that fragmentation proceeds independently of the hard sub-process.