213 research outputs found
Real and Virtual Photoproduction of Large-pt Particles at NLO
In the first part of this paper we assess the possibility of observing the
gluon distribution in a real photon by measuring the photoproduction cross
section of large-pt photons. In the second part we calculate the virtual
photoproduction of large-pt forward pi0. The theoretical results are compared
with data and with BFKL-inspired predictions. These studies are done at the NLO
approximation.Comment: Latex, 8 pages with 4 figure
Is a Large Intrinsic k_T Needed to Describe Photon + Jet Photoproduction at HERA?
We study the photoproduction of an isolated photon and a jet based on a code
of partonic event generator type which includes the full set of next-to-leading
order corrections. We compare our results to a recent ZEUS analysis in which an
effective k_T of the incoming partons has been determined. We find that no
additional intrinsic k_T is needed to describe the data.Comment: 23 pages LaTeX, 12 figure
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
Real photon structure at an e^+e^- linear collider
Previous studies of the kinematic coverage for measuring the photon structure
function F_2^gamma at a future 500 GeV e^+e^- linear collider are updated using
current estimates of luminosities and important detector parameters. The
perturbative expansion for the evolution of F_2^gamma is briefly recalled in
view of a recent claim that all existing next-to-leading order analyses of the
photon structure are incorrect. A simple illustration is given of the different
sensitivities of hadronic and photonic structure functions on the strong
coupling constant alpha_s.Comment: 6 pages LaTeX including 7 eps-figures, uses espcrc2.sty (included).
Talk presented at PHOTON'99, Freiburg (Germany), May 1999. To appear in the
proceedings [Nucl. Phys. B (Proc. Suppl.)
Next-To-Leading Order Determination of Fragmentation Functions
We analyse LEP and PETRA data on single inclusive charged hadron
cross-sections to establish new sets of Next-to-Leading order Fragmentation
Functions. Data on hadro-production of large- hadrons are also used
to constrain the gluon Fragmentation Function. We carry out a critical
comparison with other NLO parametrizations
A new critical study of photon production in hadronic collisions
In the light of the new prompt photon data collected by PHENIX at RHIC and by
D0 at the run II of the Tevatron, we revisit the world prompt photon data, both
inclusive and isolated, in hadronic collisions, and compare them with the NLO
QCD calculations implemented in the Monte Carlo programme JETPHOX.Comment: 19 pages; 12 figure
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
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