108 research outputs found
New NLO Parametrizations of the Parton Distributions in Real Photons
We present new NLO sets of parton distributions in real photons based on a
scheme invariant definition of the non-perturbative input. We compare the
theoretical predictions with LEP data and a best fit allows us to constrain the
parameters of the distributions. The shape of the gluon distribution is poorly
constrained and we consider the possibility to measure it in photoproduction
experiments. Three parametrizations which aim to take into account the
scattering of LEP data are proposed. They are compared to other NLO
parametrizations.Comment: 38 pages, 23 Postscript figures, fig. 6,7,8,9 improved, comparisons
with other NLO parametrizations, added reference
Large-p_T Inclusive pi^0 Cross Sections and Next-to-Leading-Order QCD Predictions
We review the phenomenology of pi^0 production at large transverse momentum
in proton-induced collisions. Uncertainties in the next-to-leading-order
predictions of Quantum Chromodynamics are discussed. The comparison with data
reveals that the disagreement between theory and experiment lies essentially in
an overall normalization factor. The situation for pi^0 production is
contrasted with that of prompt-photon production in hadronic collisions.Comment: 21 pages (Latex), 13 figures (Postscript
A critical phenomenological study of inclusive photon production in hadronic collisions
We discuss fixed target and ISR inclusive photon production and attempt a
comparison between theory and experiments. The dependence of the theoretical
predictions on the structure functions, and on the renormalization and
factorization scales is investigated. The main result of this study is that the
data cannot be simultaneously fitted with a single set of scales and structure
functions. On the other hand, there is no need for an additional intrinsic
to force the agreement between QCD predictions and experiments, with
the possible exception of one data set. Since the data cover almost overlapping
kinematical ranges this raises the question of consistency among data sets. A
comparative discussion of some possible sources of experimental uncertainties
is sketched.Comment: 22 pages, 3 tables, 10 figures, Late
On the photoproduction of jets at HERA
We discuss the inclusive jet production at HERA in the next-to-leading
logarithm approximation. Theoretical uncertainties are considered in some
details. We show the importance of the jet rapidity distribution to constrain
the parton densities in the photon. A comparison is made with the recent H1
data.Comment: 10 + 7 figures included uuencoded tar-compressed
([email protected]) , ENSLAPP-A-484/94, LPTHE Orsay 94-8
An NLO calculation of the electroproduction of large-E_\bot hadrons
We present a Next-to-Leading Order calculation of the cross section for the
leptoproduction of large- hadrons and we compare our predictions with
H1 data on the forward production of . We find large higher order
corrections and an important sensitivity to the renormalization and
factorization scales. These large corrections are shown to arise in part from
BFKL-like diagrams at the lowest order.Comment: 24 pages, plain LaTeX2e, 10 figure
Cross section of isolated prompt photons in hadron-hadron collisions
We consider the production of isolated prompt photons in hadronic collisions.
We present a general discussion in QCD perturbation theory of the isolation
criterion used by hadron collider experiments. The isolation criterion is
implemented in a computer programme of the Monte Carlo type, which evaluates
the production cross section at next-to-leading order accuracy in perturbative
QCD. The calculation includes both the direct and the fragmentation components
of the cross section, without any approximation of the dependence on the radius
R of the isolation cone. We examine the scale dependence of the isolated cross
section, the sensitivity of the cross section to the values of the isolation
parameters, and we provide a quantitative comparison between the full R
dependence and its small-R approximation.Comment: 29 pages, 1 figure, few comments slightly expanded, results
unchanged, misprints correcte
A Parton Shower Model for Hadronic Two-Photon Process in e^+e^- Scatterings
A new model of QCD parton shower is proposed which is dedicated to two-photon
process in scattering. When hadron jets are produced, the photon may
resolve into quark-antiquark pairs so that the structure functions of the
photon should be introduced. Based on the Altarelli-Parisi equation for these
functions, an algorithm is formulated that allows us to construct a model for
parton showers for the photon. Our model consists of two parts, one of which
describes the deep inelastic scattering of the photon and the other one the
scattering of two quasi-real photons. Using the model some results are
presented on parton distributions and jet production.Comment: LaTeX file 16 pages 7 figures available on requis
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