317 research outputs found
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 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
Diffractive charm photoproduction at HERA ep-collider
The cross section of the -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
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
Determination of the longitudinal structure function at HERA
Recent results from the HERA experiment H1 on the longitudinal stucture
function of the proton are presented. They include proton structure
function analyses with particular emphasis on those kinematic regions which are
sensitive to . All results can be consistently described within the
framework of perturbative QCD.Comment: 16 pages, 11 figures (requires iopart, iopams and epsfig); Talk
presented in the Intern. Workshop on New Trends in HERA Physics 2001, 17-22
June 2001, Ringberg Castle, Tegernsee, Germany; To appear in the Proceeding
Open Heavy Flavor Production in QCD -- Conceptual Framework and Implementation Issues
Heavy flavor production is an important QCD process both in its own right and
as a key component of precision global QCD analysis. Apparent disagreements
between fixed-flavor scheme calculations of b-production rate with experimental
measurements in hadro-, lepto-, and photo-production provide new impetus to a
thorough examination of the theory and phenomenology of this process. We review
existing methods of calculation, and place them in the context of the general
PQCD framework of Collins. A distinction is drawn between scheme dependence and
implementation issues related to quark mass effects near threshold. We point
out a so far overlooked kinematic constraint on the threshold behavior, which
greatly simplifies the variable flavor number scheme. It obviates the need for
the elaborate existing prescriptions, and leads to robust predictions. It can
facilitate the study of current issues on heavy flavor production as well as
precision global QCD analysis.Comment: 13 pages, 10 figures, Proceedings of Ringberg Workshop: New Trends in
HERA Physics 2001, Munich, German
Saturation and geometric scaling in DIS at small x
We present various aspects of the saturation model which provides good
description of inclusive and diffractive DIS at small x. The model uses parton
saturation ideas to take into account unitarity requirements. A new scaling
predicted by the model in the small x domain is successfully confronted with
the data.Comment: Presented at New Trends in HERA Physics 2001, Ringberg Castle,
Tegernsee, Germany, 17-22 June 2001, minor corrections, some references adde
Uncertainties on parton distribution functions from the ZEUS NLO QCD fit to data on deep inelastic scattering
An NLO QCD analysis of the ZEUS data on deep inelastic scattering
together with fixed-target data has been performed from which the gluon and
quark densities of the proton and the value of the strong coupling parameter,
, have been extracted. The study includes a full treatment of
the experimental systematic uncertainties, including point-to-point
correlations. Different ways of incorporating correlated systematic
uncertainties into the fit are discussed and compared.Comment: 8 pages, 1 figure. Invited talk at the Conference on Advanced
Statistical Techniques in Particle Physics, March 18-22 2002, Durham, U
Regge behaviour of distribution functions and t and x-evolutions of gluon distribution function at low-x
In this paper t and x-evolutions of gluon distribution function from
Dokshitzer-Gribov-Lipatov-Altarelli-Parisi(DGLAP) evolution equation in leading
order(LO) at low-x, assuming the Regge behaviour of quark and gluon at this
limit, are presented. We compare our results of gluon distribution function
with MRST 2001, MRST 2004 and GRV '98 parameterizations and show the
compatibility of Regge behaviour of quark and gluon distribution functions with
perturbative quantum chromodynamics(PQCD) at low-x. We also discuss the
limitations of Taylor series expansion method used earlier to solve DGLAP
evolution equations, in the Regge behaviour of distribution functions.Comment: 19 pages, 7 figure
pQCD Calculations of Heavy Quark and J/psi Production
We review the present status of theoretical predictions for both closed
(J/psi) and open heavy quark production in high energy collisions, and their
comparisons to experimental data.Comment: 8 pages, invited talk given at Quark Matter 2006, Shanghai, China,
14-20 November 200
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