425 research outputs found
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
Recent Low x and Diffractive Collider Data
Selected recent data from collider experiments pertaining to the
understanding of QCD at low Bjorken-x are reviewed. The status of QCD and Regge
factorisation in hard diffractive interactions is discussed in terms of data
from HERA and the Tevatron. The possibility of anomalous behaviour in the
total cross section is confronted with the most recent
measurements from LEP. Data from all three colliders that are sensitive to
possible BFKL effects are presented and different interpretations are
discussed.Comment: 9 pages, introductory talk from the 1999 Durham Phenomenology
Workshop on Collider Physic
Momentum Spectra in the Current Region of the Breit Frame in Deep Inelastic Scattering at HERA
The production of charged particles has been measured in deep inelastic
scattering (DIS) with the ZEUS detector. The evolution of the moments of the
scaled momenta distributions in and has been investigated in the
current fragmentation region of the Breit frame. The results in the current
region are compared to data and QCD analytical calculations. The
results are consistent with the universality of single-particle spectra in DIS
and annihilation at high The results at low disagree with
analytical calculations based on the modified leading log approximation (MLLA)
and local parton hadron duality (LPHD).Comment: 3 pages. 1 postscript figure + 1 postscript preprint logo + 1 LaTeX
file + 1 style fil
A characteristic plot of pomeron-exchanged processes in diffractive DIS
The dependence of the fractal behaviors of the pomeron induced system in deep
inelastic lepton-nucleon scattering upon the diffractive kinematic variables is
found rather robust and not sensitive to the distinct parameterization of the
pomeron flux factor and structure function. A feasible experimental test of the
phenomenological pomeron-exchanged model based on the fractal measurement in
DESY collider HERA is proposed.Comment: 14 pages, 2 Postscript figure
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
Bayesian model comparison applied to the Explorer-Nautilus 2001 coincidence data
Bayesian reasoning is applied to the data by the ROG Collaboration, in which
gravitational wave (g.w.) signals are searched for in a coincidence experiment
between Explorer and Nautilus. The use of Bayesian reasoning allows, under well
defined hypotheses, even tiny pieces of evidence in favor of each model to be
extracted from the data. The combination of the data of several experiments can
therefore be performed in an optimal and efficient way. Some models for
Galactic sources are considered and, within each model, the experimental result
is summarized with the likelihood rescaled to the insensitivity limit value
(`` function''). The model comparison result is given in in terms of
Bayes factors, which quantify how the ratio of beliefs about two alternative
models are modified by the experimental observationComment: 16 pages, 4 figures. Presented at the GWDAW2002 conference, held in
Kyoto on Dec.,2002. This version includes comments by the referees of CQG,
which has accepted the paper for pubblication in the special issue of the
conference. In particular, note that in Eq. 12 there was a typeset error. As
suggested by one of the referees, a uniform prior in Log(alpha) has also been
considere
Heavy Quark Mass Effects in Deep Inelastic Scattering and Global QCD Analysis
A new implementation of the general PQCD formalism of Collins, including
heavy quark mass effects, is described. Important features that contribute to
the accuracy and efficiency of the calculation of both neutral current (NC) and
charged current (CC) processess are explicitly discussed. This new
implementation is applied to the global analysis of the full HERA I data sets
on NC and CC cross sections, with correlated systematic errors, in conjunction
with the usual fixed-target and hadron collider data sets. By using a variety
of parametrizations to explore the parton parameter space, robust new parton
distribution function (PDF) sets (CTEQ6.5) are obtained. The new quark
distributions are consistently higher in the region x ~ 10^{-3} than previous
ones, with important implications on hadron collider phenomenology, especially
at the LHC. The uncertainties of the parton distributions are reassessed and
are compared to the previous ones. A new set of CTEQ6.5 eigenvector PDFs that
encapsulates these uncertainties is also presented.Comment: 32 pages, 12 figures; updated, Publication Versio
Open charm production in diffractive ep collisions
The cross section for the diffractive reaction gamma* + p -> c cbar + p with
a real or virtual photon is calculated in the nonperturbative two-gluon
exchange model of Landshoff and Nachtmann. Numerical predictions are given for
cross sections and spectra at typical HERA values of c.m. energy and photon
virtuality. The contribution of charm to the diffractive structure function is
evaluated and found to be rather small in the model, and the ratio between the
production rates for b bbar and c cbar is tiny.Comment: 16 pages including 7 figures, Latex2e, uses epsf.st
Factorization scheme and scale dependence in diffractive dijet production at low Q^2
We calculate diffractive dijet production in deep-inelastic scattering at
next-to-leading order of perturbative QCD, including contributions from direct
and resolved photons, and compare our predictions to preliminary data from the
H1 collaboration at HERA. We study how the cross section depends on the
factorization scheme and scale M_\gamma at the virtual photon vertex for the
occurrence of factorization breaking. The strong M_\gamma-dependence, which is
present when only the resolved cross section is suppressed, is tamed by
introducing the suppression also into the initial-state NLO correction of the
direct part.Comment: 14 pages, 6 figure
The DVCS Measurement at HERA
The recent results of the studies of Deeply Virtual Compton Scattering (DVCS)
events at HERA are presented. The possibility offered by this process to gain
information about skewed parton distributions (SPD) is emphasized.Comment: Talk given at New Trends in HERA Physics 2001, Ringberg Castle,
Tegernsee, Germany, 17-22 Jun 2001, 13 pages, 10 figures, recent ZEUS data
discussed, references update
- …