Final state correlations in open charm production at HERA

Open charm production in electron-proton (ep) scattering at the high energies of HERA (centreof-mass energy √ s ∼ 320 GeV) is an ideal tool to study perturbative Quantum Chromodynamics (pQCD), since the charm mass provides a hard scale. The main charm production mechanism is photon-gluon fusion (PGF) where a photon emitted by the incoming electron interacts with a gluon in the proton forming a quark antiquark pair. The cross section is dominated by processes where the virtuality Q2 of the exchanged photon is very small. The kinematic region of Q2 < 1 GeV2 is generally referred to as photoproduction since the photon is almost real. In this regime resolved photon processes in which the photon ¤uctuates into a hadronic state before the hard interaction, become important. Investigating £nal state correlations increases the sensitivity to the details of the charm production mechanism. Here H1 and ZEUS measurements of D∗+jet cross sections in photoproduction are presented. Comparing the pseudorapidity distributions of the D∗ and a jet not containing the D∗ reveals the presence of non-charm initiated jets. The difference in the azimuthal angle φ between the two highest pt jets shows the need for higher order contributions to describe the data. Furthermore results from H1 investigations of the integrated jet shape in dijet events are shown, where charm is tagged by a muon. The observations contradict the Monte Carlo expectation of broad gluon initiated jets in a resolved enriched data sample.