Measurement of D*+/- diffractive cross sections in photoproduction at HERA

The first measurement of D*+/- meson diffractive photoproduction cross sections has been performed with the ZEUS detector at the HERA $ep$ collider, using an integrated luminosity of 38 pb^-1. The measurement has been performed for photon--proton center-of-mass energies in the range 130 < W < 280 GeV and photon virtualities Q^2 < 1 GeV^2. D*+/- mesons have been reconstructed with p_T(D*)>2 GeV and -1.5 D^0 \pi^+_s with D^0 --> K-\pi^+ (+c.c.). The diffractive component has been selected with 0.001<x_Pom<0.018. The measured diffractive cross section in this kinematic range is: \sigma_(ep --> e'D*Xp') = 0.74 +/- 0.21 (stat.)^{+0.27}_{-0.18} (syst.) +/-0.16 (p. diss.) ~nb (ZEUS preliminary). Measured integrated and differential cross sections have been compared to theoretical expectations.Comment: LaTeX2e, 10 pages, 6 Postscript figures. Talk given at the Russian Academy of Science (RAS) Nuclear Physics 2000 Conference, Moscow, Russia, November 27-December 2, 2000. To be published in Rus. Nucl. Phys. (Ya.F.), Proceedings of RAS Nucl. Phys. 2000 Con

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

Diffractive phenomena

The most recent theoretical and experimental results in the field of diffractive scattering are reviewed. A parallel between the two current theoretical approaches to diffraction, the DIS picture in the Breit frame and the dipole picture in the target frame, is given, accompanied by a description of the models to which the data are compared. A recent calculation of the rescattering corrections, which hints at the universality of the diffractive parton distribution functions, is presented. The concept of generalized parton distributions is discussed together with the first measurement of the processes which might give access to them. Particular emphasis is given to the HERA data, to motivate why hard diffraction in deep inelastic scattering is viewed as an unrivalled instrument to shed light on the still obscure aspects of hadronic interactions.Comment: invited talk at the XX International Symposium on Lepton and Photon Interactions at High Energies, Rome, Italy, July 200

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

Photoproduction and electroproduction of charm at high energies

We estimate the differential and total cross sections for both the photoproduction of vector D*-meson and its yield in deep inelastic scattering at the HERA collider in the framework of model motivated by perturbative calculations in QCD. The offered model allows us to take into account higher twists over the transverse momentum of meson at p_T ~ m_c and to correctly approach the dominance of $c$-quark fragmentation at p_T >> m_c. We consider a possibility for the hadronization of color-octet c q-bar state into the meson. The combined contribution by the singlet and octet-color terms results in a good agreement with the experimental data for both the photoproduction and the production in deep inelastic scattering.Comment: 27 pages, ReVTeX, 8 eps-figures, explanations added, results unchange

From the exclusive photoproduction of heavy quarkonia at HERA to the EDDE at TeVatron and LHC

Exclusive photoproduction of heavy quarkonia at HERA is analyzed in the framework of the Regge-eikonal approach together with the nonrelativistic bound state formalism. Total and differential cross-sections for the process $\gamma+p\to (Q\bar{Q})_{1S}+p$ are calculated. The model predicts cross-sections of Exclusive Double Diffractive Events (EDDE) at TeVatron and LHC.Comment: 14 pages, 6 figures, reference is adde

Heavy Quark Hadroproduction in kTk_T-Factorization Approach with Unintegrated Gluon Distributions

We consider the processes of compare the heavy quark production using the unintegrated gluon distributions. The numerical predictions for high energy nucleon-nucleon and photon-nucleon collisions of the $k_T$-factorization approach (semihard theory) are compared with the experimental data from Tevatron-collider and HERA. The total production cross sections and $p_T$ distributions are considered and they are in reasonable agreement with the data for rather value of QCD scale.Comment: 21 pages, 10 figures, references adde

Antikaon angular distributions in the reaction γd→K−Θ+p→K−K+np{\gamma}d \to K^-{\Theta}^+p \to K^-K^+np near the threshold and the parity of the Θ+{\Theta}^+ pentaquark

Within spectator model we study the reaction ${\gamma}d \to K^-{\Theta}^+p \to K^-K^+np$ in the threshold energy region. We present the predictions for the exclusive and inclusive antikaon angular distributions in the laboratory system for this reaction calculated for two possible parity states of the ${\Theta}^+$ resonance at 1.5 and 1.75 GeV beam energies with and without imposing the relevant kinematical cuts on those parts of the sampled phase space where contribution from the main background sources associated with the ${\phi}(1020)$, ${\Lambda}(1520)$ production as well as with the $K^-p$--rescattering in the final state, is expected to be dominant. We show that under chosen kinematics these distributions are sensitive to the ${\Theta}^+$ parity and, therefore, can be used as a filter for the determination of its parity.Comment: 18 pages, 8 figures; will be published in Phys.Atom.Nucl_4_200

Complete O(alpha_s^2) Corrections to (2+1) Jet Cross Sections in Deep Inelastic Scattering

Complete next-to leading order QCD predictions for (2+1) jet cross sections and jet rates in deep inelastic scattering (DIS) based on a new parton level Monte Carlo program are presented. All relevant helicity contributions to the total cross section are included. Results on total jet cross sections as well as differential distributions in the basic kinematical variables $x,W^2$ and $Q^2$ are shown for HERA energies and for the fixed target experiment E665 at FERMILAB. We study the dependence on the choices of the renormalization scale $\mu_R$ and the factorization scale $\mu_F$ and show that the NLO results are much less sensitive to the variation of $\mu=\mu_F=\mu_R$ than the LO results. The effect of an additional $p_T$ cut to our jet definition scheme is investigated.Comment: 14 pages, LateX, MAD/PH/821, 15 figures (not included), figures are available upon request. (some essential changes to the figures, minor changes to the text). To appear in Z.Phys.