Nuclear shadowing at low Q^2

We re-examine the role of vector meson dominance in nuclear shadowing at low Q^2. We find that models which incorporate both vector meson and partonic mechanisms are consistent with both the magnitude and the Q^2 slope of the shadowing data.Comment: 7 pages, 2 figures; to appear in Phys. Rev.

Heavy Quark Photoproduction in Ultra-peripheral Heavy Ion Collisions

Heavy quarks are copiously produced in ultra-peripheral heavy ion collisions. In the strong electromagnetic fields, c c-bar and b b-bar are produced by photonuclear and two-photon interactions; hadroproduction can occur in grazing interactions. We present the total cross sections, quark transverse momentum and rapidity distributions, as well as the Q Q-bar invariant mass spectra from the three production channels. We consider AA and pA collisions at the Relativistic Heavy Ion Collider and Large Hadron Collider. We discuss techniques for separating the three processes and describe how the AA to pA production ratios might be measured accurately enough to study nuclear shadowing.Comment: Minor changes to satisfy referees and typo fixes; 52 pages including 17 figure

Uncertainties of the CJK 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, calculated in the CJK model being an improved realization of the CJKL approach, have been recently presented. The results were obtained through a global fit to the experimental F2^gamma data. In this paper we present, obtained for the very first time in the photon case, an estimate of the uncertainties of the CJK parton distributions due to the experimental errors. The analysis is based on the Hessian method which was recently applied in the proton parton structure analysis. Sets of test parametrizations are given for the CJK model. They allow for calculation of its best fit parton distributions along with F2^gamma and for computation of uncertainties of any physical value depending on the real photon parton densities. We test the applicability of the approach by comparing uncertainties of example cross-sections calculated in the Hessian and Lagrange methods. Moreover, we present a detailed analysis of the chi^2 of the CJK fit and its relation to the data. We show that large chi^2/DOF of the fit is due to only a few of the experimental measurements. By excluding them chi^2/DOF approx 1 can be obtained.Comment: 28 pages, 8 eps figures, 2 Latex figures; FORTRAN programs available at http://www.fuw.edu.pl/~pjank/param.html; table 10, figure 10 and section 6 correcte

Testing Color Evaporation in Photon-Photon Production of J/Psi at CERN LEP II

The DELPHI Collaboration has recently reported the measurement of J/Psi production in photon-photon collisions at LEP II. These newly available data provide an additional proof of the importance of colored c bar{c} pairs for the production of charmonium because these data can only be explained by considering resolved photon processes. We show here that the inclusion of color octet contributions to the J/Psi production in the framework of the color evaporation model is able to reproduce this data. In particular, the transverse-momentum distribution of the J/Psi mesons is well described by this model.Comment: 10 pages, 5 Figures, Revtex

Parton content of the real photon: astrophysical implications

We possess convincing experimental evidence for the fact that the real photon has non-trivial parton structure. On the other hand, interactions of the cosmic microwave background photons with high energy particles propagating through the Universe play an important role in astrophysics. In this context, to invoke the parton content could be convenient for calculations of the probabilities of different processes involving these photons. As an example, the cross section of inclusive resonant $W^+$ boson production in the reaction $\nu \gamma\to W^+X$ is calculated by using the parton language. Neutrino--photon deep inelastic scattering is considered.Comment: 4 pages, 2 figures. The spin states of the initial particles in the reaction $\nu\gamma\to W^+X$ are correctly treated. As a result, the corresponding cross section becomes two times greater than the one from the previous version. Some changes in the tex

Hard diffractive quarkonium hadroproduction at high energies

We present a study of heavy quarkonium production in hard diffractive process by the Pomeron exchange for Tevatron and LHC energies. The numerical results are computed using recent experimental determination of the diffractive parton density functions in Pomeron and are corrected by unitarity corrections through gap survival probability factor. We give predictions for single as well as central diffractive ratios. These processes are sensitive to the gluon content of the Pomeron at small Bjorken-x and may be particularly useful in studying the small-x physics. They may also be a good place to test the different available mechanisms for quarkonium production at hadron colliders.Comment: 7 pages, 3 figures, 1 table. Final version to be published in European Physical Journal

Low- and high-mass components of the photon distribution functions

The structure of the general solution of the inhomogeneous evolution equations allows the separation of a photon structure function into perturbative (``anomalous") and non-perturbative contributions. The former part is fully calculable, and can be identified with the high-mass contributions to the dispersion integral in the photon mass. Properly normalized ``state" distributions can be defined, where the \gamma\to\qqbar splitting probability is factored out. These state distributions are shown to be useful in the description of the hadronic event properties, and necessary for a proper eikonalization of jet cross sections. Convenient parametrizations are provided both for the state and for the full anomalous parton distributions. The non-perturbative parts of the parton distribution functions of the photon are identified with the low-mass contributions to the dispersion integral. Their normalizations, as well as the value of the scale $Q_0$ at which the perturbative parts vanish, are fixed by approximating the low-mass contributions by a discrete, finite sum of vector mesons. The shapes of these hadronic distributions are fitted to the available data on $F_2^\gamma(x,Q^2)$. Parametrizations are provided for $Q_0=0.6\,$GeV and $Q_0=2\,$GeV, both in the DIS and the $\overline{\mathrm{MS}}$ factorization schemes. The full parametrizations are extended towards virtual photons. Finally, the often-used ``FKP-plus-TPC/$2\gamma$" solution for $F_2^\gamma(x,Q^2)$ is commented upon.Comment: 33 pages, Latex, 6 Z-compressed and uuencoded figure

Charm quark and D^* cross sections in deeply inelastic scattering at DESY HERA

A next-to-leading order Monte Carlo program for the calculation of heavy quark cross sections in deeply inelastic scattering is described. Concentrating on charm quark and D^*(2010) production at HERA, several distributions are presented and their variation with respect to charm quark mass, parton distribution set, and renormalization-factorization scale is studied.Comment: 15 pages including 8 figures. Uses Latex, Revtex, and psfig. References added - others updated. Several sentences/words added for clarity. Results/conclusions unchanged. To appear in Phys. Rev.

Discovery and Identification of W' Bosons in e gamma to nu q +X

We examine the sensitivity of the process e gamma to nu q +X to W' bosons which arise in various extensions of the standard model. We consider photon spectra from both the Weizsacker Williams process and from a backscattered laser. The process is found to be sensitive to W' masses up to several TeV, depending on the model, the center of mass energy, the integrated luminosity, and assumptions regarding systematic errors. If extra gauge bosons were discovered first in other experiments, the process could also be used to measure W' couplings. This measurement would provide information that could be used to unravel the underlying theory, complementary to measurements at the Large Hadron Collider.Comment: 17 pages, 9 figures, uses Revtex and epsfi

Measuring Parton Densities in the Pomeron

We present a program to measure the parton densities in the pomeron using diffractive deep inelastic scattering and diffractive photoproduction, and to test the resulting parton densities by applying them to other processes such as the diffractive production of jets in hadron-hadron collisions. Since QCD factorization has been predicted NOT to apply to hard diffractive scattering, this program of fitting and using parton densities might be expected to fail. Its success or failure will provide useful information on the space-time structure of the pomeron.Comment: Contains revisions based on Phys. Rev. D referee comments. RevTeX version 3, epsf, 31 pages. Uuencoded compressed postscript figures appended. Uncompressed postscript files available at ftp://ftp.phys.psu.edu/pub/preprint/psuth136