CJK-Improved 5 Flavour LO Parton Distributions in the Real Photon

Radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real, unpolarized photon, improved in respect to our previous paper, are presented. We perform three global fits to the F_2^gamma data, using the LO DGLAP evolution equation. We improve the treatment of the strong coupling running and used lower values of Lambda_QCD, as we have found that the too high values adopted in the previous work caused the high chi^2 of the fits. In addition to the modified FFNS_CJKL model, referred to as FFNS_CJK 1 we analyse a FFNS_CJK 2 model in which we take into account the resolved-photon heavy-quark contribution. New CJK model with an improved high-x behavior of the F_2^gamma(x,Q^2) is proposed. Finally, in the case of the CJK model we abandon the valence sum rule imposed on the VMD input densities. New fits give chi^2 per degree of freedom about 0.25 better than the old results. All features of the CJKL model, such as the realistic heavy-quark distributions, good description of the LEP data on the Q^2 dependence of the F_2^gamma and on F_2,c^gamma are preserved. Moreover we present results of an analysis of the uncertainties of the CJK parton distributions due to the experimental errors. It is based on the Hessian method used for the proton and very recently applied for the photon by one of us. Parton and structure function parametrizations of the best fits in both FFNS_CJK and CJK approaches are made accessible. For the CJK model we provide also sets of test parametrizations which allow for calculation of uncertainties of any physical value depending on the real photon parton densities.Comment: 27 pages, 14 figures, FORTRAN programs available at http://www.fuw.edu.pl/~pjank/param.htm

Nuclear effects in photoproduction of heavy quarks and vector mesons in ultraperipheral PbPb and pPb collisions at the LHC

The comparison of photoproduction cross sections for $c\bar{c}$ and b-b(bar) in PbPb and pPb collisions can give sensitivity to nuclear shadowing effects. The photoproduction of vector mesons is even more sensitive to the underlying gluon distributions. In this study we present the cross sections and rapidity dependence of the photoproduction of heavy quarks and exclusive production of vector mesons in ultraperipheral pPb and PbPb collisions at the Large Hadron Collider at sqrt(s_NN)=5 TeV and sqrt(s_NN)=2.76$TeV, respectively. The potentials of using these processes for constraining nuclear gluon shadowing are explored. It is found that photoproduction of$J/\psi$and$\Upsilon$ in PbPb collisions in particular exhibit very good sensitivity to gluon shadowing.Comment: 4 pages, 4 figure

Constraining Gluon Shadowing Using Photoproduction in Ultraperipheral pA and AA Collisions

Photoproduction of heavy quarks and exclusive production of vector mesons in ultraperipheral proton-nucleus and nucleus-nucleus collisions depend significantly on nuclear gluon distributions. In the present study we investigate quantitatively the extent of the applicability of these processes at the Large Hadron Collider (LHC) in constraining the shadowing component of nuclear gluon modifications.Comment: 15 pages, 10 figures. arXiv admin note: substantial text overlap with arXiv:1104.428

Contact terms in charged current processes at HERA

We obtain bounds on the mass scales characterizing four-fermion contact interactions in charged current processes. The bounds arise from the Q^2 and x distributions in the processes e p -> \nu X measured by the two HERA experiments, H1 and ZEUS

CJK- Improved LO Parton Distributions in the Real Photon and Their Experimental Uncertainties

A new analysis of the radiatively generated, LO quark (u,d,s,c,b) and gluon densities in the real, unpolarized photon, improved in respect to our paper [1], is presented. We perform four new global fits to the experimental data for F2^gamma, two using a standard FFNS approach and two based on ACOT(chi) scheme [2], leading to the FFNS(CJK) and CJK models. We also present the analysis of the uncertainties of the new CJK 2 parton distributions due to the experimental errors, the very first such analysis performed for the photon. This analysis is based on the Hessian method, for a comparison for chosen cross-sections we use also the Lagrange method.Comment: Prepared for Photon 2003: International Conference on the Structure and Interactions of the Photon (Including the 15th International Workshop on Photon-Photon Collisions), Frascati (Italy), 7-11 April 2003; 10 pages, Latex using espcrc2 style, 1 tex and 5 postscript figures; FORTRAN programs available at http://www.fuw.edu.pl/~pjank/param.htm