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Measurement of charm fragmentation ratios and fractions in photoproduction at HERA
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DESY–05–147
August 2005
Measurement of charm fragmentation ratios
and fractions in photoproduction at HERA
ZEUS Collaboration
Abstract
The production of D?+, D0, D+, D+s and Λ
+
c charm hadrons and their antipar-
ticles 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 300GeV.
The charm hadrons were reconstructed in the range of transverse momentum
pT (D,Λc) 3.8GeV and pseudorapidity |η(D,Λc)| 1.6. The production cross
sections were used to determine the ratio of neutral and charged D-meson pro-
duction rates, Ru/d, the strangeness-suppression factor, γs, and the fraction of
charged D mesons produced in a vector state, P dv . The measured Ru/d and γs
values agree with those obtained in deep inelastic scattering and in e+e? an-
nihilations. The measured P dv value is smaller than, but consistent with, the
previous measurements. The fractions of c quarks hadronising as a particular
charm hadron, f(c → D,Λc), were derived in the given kinematic range. The
measured open-charm fragmentation fractions are consistent with previous re-
sults, 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.
The ZEUS Collaboration
S. Chekanov, M. Derrick, S. Magill, S. Miglioranzi1, B. Musgrave, J. Repond, R. Yoshida
Argonne National Laboratory, Argonne, Illinois 60439-4815, USA n
M.C.K. Mattingly
Andrews University, Berrien Springs, Michigan 49104-0380, USA
N. Pavel, A.G. Yagu?es Molina
Institut fu?r Physik der Humboldt-Universita?t zu Berlin, Berlin, Germany
P. Antonioli, G. Bari, M. Basile, L. Bellagamba, D. Boscherin
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