Open Charm Production at HERA

Measurements of charmed particle cross sections at HERA in the photoproduction and deep inelastic regimes are reviewed. The status of the comparison with perturbative QCD calculations is discussed.Comment: Presented at the Ringberg Workshop on ``New Trends in HERA Physics 2001'' 17-22 June 2001. 12 pages, 11 figure

Production of J/psi Mesons at HERA

Inelastic and diffractive production of J/psi mesons at HERA is reviewed. The data on inelastic photoproduction are described well within errors by the Colour Singlet Model in next-to-leading order. A search for colour octet processes predicted within the NRQCD/factorisation approach is conducted in many regions of phase space. No unambiguous evidence has been found to date. Diffractive elastic production of J/psi mesons has been measured in the limit of photoproduction up to the highest photon proton center of mass energies. The increase of the cross section is described by pQCD models. At larger Q^2, the W dependence is found to be similar to that observed in photoproduction. First analyses of data at high t yield a powerlike dependence on |t|. A LO BFKL calculation gives a good description of the data.Comment: 14 pages, 12 figures, contribution to Ringberg 200

Lower bounds for open charm and beauty contributions to F_2

On the basis of some peculiar scaling properties of the OPE coefficient functions, we give the lower bounds for F_2^{c\bar{c}} and F_2^{b\bar{b}} independently of the properties of the gluon density function. Predictions for F_2^{b\bar{b}} within reach of HERA are made.Comment: 10 pages, 4 eps figures. Misprints are corrected and comment is added. To appear in JHE

Structure functions at large x

Structure function data together with other measurements from fixed-target deep inelastic scattering and hadron-hadron collider experiments which contribute to our knowledge of the parton density functions are reviewed. The inclusive cross-section measurements of neutral and charged current interactions at HERA are presented and their impact on the parton density functions is discussed. Future prospects for an improved knowledge of the parton density functions at large x are briefly mentioned.Comment: Invited talk given at the workshop on ``New Trends in HERA Physics 2001'', Ringberg castle, Germany, June 17-22, 200

Heavy Flavour Physics at HERA - a Survey

At the HERA collider at DESY, high energy electron and positron beams interact with proton beams. A review is presented of the variety of ways in which these collisions produce final states containing charm and beauty quarks.Comment: 45 pages including 30 figures. Submitted to International Journal of Modern Physics

Measurement of D^\pm Production in Deep Inelastic ep Scattering with the ZEUS Detector at HERA

Charm production in deep inelastic ep scattering was measured with the ZEUS detector using an integrated luminosity of 354 pb^{-1}. Charm quarks were identified by reconstructing D^{+} mesons in the D^{+} -\u3e K^{-} pi^{+} pi^{+} decay channel. Lifetime information was used to reduce combinatorial background substantially. Differential cross sections were measured in the kinematic region 5 \u3c Q^{2} \u3c 1000 GeV^{2}, 0.02 \u3c y \u3c 0.7, 1.5 \u3c p_{T}(D^{+}) \u3c 15 GeV and |eta(D^{+})| \u3c 1.6, where Q^{2} is the photon virtuality, y is the inelasticity, and p_{T}(D^{+}) and eta(D^{+}) are the transverse momentum and the pseudorapidity of the D^{+} meson, respectively. Next-to-leading-order QCD predictions are compared to the data. The charm contribution, F_{2}^{cc}, to the proton structure-function F_{2} was extracted

Measurement of D^*\pm Production in Deep Inelastic Scattering at HERA

The production of D∗± mesons in deep inelastic ep scattering has been measured for exchanged photon virtualities 5 \u3c Q2\u3c1000GeV2, using an integrated luminosity of 363 pb−1 with the ZEUS detector at HERA. Differential cross sectionshave been measured and compared to next-to-leading-order QC D calculations. The cross-sections are used to extract the charm contribution to the protonstructure functions, expressed in terms of the reduced charm cro ss section, σc̄cred. Theoretical calculations based on fits to inclusive HERA data are compared to the results

Deep Inelastic Scattering at HERA

Results from the H1 and ZEUS experiments at HERA on deep inelastic scattering are reviewed. The data lead to a consistent picture of a steep rise in the F_2 structure function and in the gluon density within the proton. Important new information on the partonic structure of diffraction is emerging from H1 and ZEUS. The space-like region in which the weak and electromagnetic interactions become of equal strength is being explored for the first time. A possible excess of events at high x and Q^2 compared to the expectations of the Standard Model has been observed in both experiments.Comment: 80 pages, 42 figure

Diffractive charm photoproduction at HERA ep-collider

The cross section of the $D^*$-meson diffractive photoproduction at the HERA collider has been calculated in the framework of perturbatively motivated model for the different kinematic regions. The camparison between the different Pomeron models has been performed.Comment: 9 pages, 3 figure