Measurement of charm fragmentation ratios and fractions in photoproduction at HERA

The production of D^{∗ +}, D⁰, D⁺, D⁺ _s and Λ⁺ _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 Q² < 1GeV² 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,Λ_c) > 3.8GeV and pseudorapidity |η(D,Λ_c)| < 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, γ_s, and the fraction of charged D mesons produced in a vector state, P^d _v. The measured R_u/d and γ_s values agree with those obtained in deep inelastic scattering and in e⁺e^- annihilations. The measured P^d _v value is smaller than, but consistent with, the previous measurements. The fractions of c quarks hadronising as a particular charm hadron, f(c → D, Λ_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 → Λ⁺ _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.