Polarization phenomena in open charm photoproduction processes

We analyze polarization effects in associative photoproduction of pseudoscalar ($\bar{D}$) charmed mesons in exclusive processes $\gamma+ N\to Y_c +\bar{D}$, $Y_c=\Lambda_c^+$, $\Sigma_c$. Circularly polarized photons induce nonzero polarization of the $Y_c$-hyperon with $x$- and $z$-components (in the reaction plane) and non vanishing asymmetries ${\cal A}_x$ and ${\cal A}_z$ for polarized nucleon target. These polarization observables can be predicted in model-independent way for exclusive $\bar{D}$-production processes in collinear kinematics. The T-even $Y_c$-polarization and asymmetries for non-collinear kinematics can be calculated in framework of an effective Lagrangian approach. The depolarization coefficients $D_{ab}$, characterizing the dependence of the $Y_c$-polarization on the nucleon polarization are also calculated.Comment: 36 pages 13 figure

Exclusive [Rho] 0 and [Phi] muoproduction at large Q 2

Arneodo M, Arvidson A, Badelek B, et al. Exclusive [Rho] 0 and [Phi] muoproduction at large Q 2. Nucl.Phys. B. 1994;429(3):503-529

Measurement of diffractive production of D*+-(2010) mesons in deep inelastic scattering at HERA

Diffractive production of D*+-(2010) mesons in deep inelastic scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 44.3 pb-1. Diffractive charm production is identified by the presence of a large rapidity gap in the final state of events in which a D*+-(2010) meson is reconstructed in the decay channel D*+ -> (D0 -> K-pi+) pi+ (+ charge conjugate). Differential cross sections when compared with theoretical predictions indicate the importance of gluons in such diffractive interactions.Comment: 19 pages, 4 figures; Submitted to Physics Letters. Comments from Journal referee incorporated, including one additional referenc

Exclusive electroproduction of phi mesons at HERA

Exclusive electroproduction of phi mesons has been studied in e (+/-) p collisions at root s = 318 GeV with the ZEUS detector at HERA using an integrated luminosity of 65.1 pb(-l). The gamma*p crosssection is presented in the kinematic range 2 GeV(2) < Q(2) < 70 GeV(2), 35 GeV < W < 145 GeV and vertical bar t vertical bar < 0.6 GeV(2). The cross sections as functions of Q(2), W, t and helicity angle phi(h) are compared to cross sections for other vector mesons. The ratios R of the cross sections for longitudinally and transversely polarized virtual photons are presented as functions of Q2 and W. The data are also compared to predictions from theoretical models. (c) 2005 Elsevier B.V. All rights reserved

Measurement of exclusive omega electroproduction at HERA

The exclusive electroproduction of omega mesons, ep -> e omega p, has been studied in the kinematic range 3<Q^2<20 GeV^2, 40<W<120 GeV and |t|<0.6 GeV^2 with the ZEUS detector at HERA using an integrated luminosity of 37.7 pb^{-1}. The omega mesons were identified via the decay omega -> pi^+pi^-pi^0. The exclusive (ep -> e omega p) cross section in the above kinematic region is 0.108 +- 0.014(stat.) +- 0.026(syst.) nb. The reaction ep -> e phi p, phi -> pi^+pi^-pi^0, has also been measured. The cross sections, as well as the cross-section ratios omega/rho and omega/phi, are presented as a function of W and Q^2. Thus, for the first time, the properties of omega electroproduction can be compared to those of rho^0, phi and J/psi electroproduction at high W.Comment: 15 pages including 4 figure

Diffractive Photoproduction of~ {\it \boldmath D∗±(2010)D^{*\pm}(2010)} at HERA

Diffractive photoproduction of D*+/-(2010) mesons was measured with the ZEUS detector at the ep collider HERA, using an integrated luminosity of 78.6 pb^{-1}. The D* mesons were reconstructed in the kinematic range: transverse momentum p_T(D*) > 1.9 GeV and pseudorapidity |eta(D*)| < 1.6, using the decay D*+ -> D0 pi+_s followed by D0 -> K- pi+ (+c.c.). Diffractive events were identified by a large gap in pseudorapidity between the produced hadronic state and the outgoing proton. Cross sections are reported for photon-proton centre-of-mass energies in the range 130 < W < 300 GeV and for photon virtualities Q^2 < 1 GeV^2, in two ranges of the Pomeron fractional momentum x_pom < 0.035 and x_pom < 0.01. The relative contribution of diffractive events to the inclusive D*+/-(2010) photoproduction cross section is about 6%. The data are in agreement with perturbative QCD calculations based on various parameterisations of diffractive parton distribution functions. The results are consistent with diffractive QCD factorisation.Comment: LaTeX2e, 29 pages, 9 Postscript figures, 4 tables, minor revisions, accepted for publication in the European Physical Journal