17 research outputs found
BFKL predictions at small x from k_T and collinear factorization viewpoints
Hard scattering processes involving hadrons at small are described by a
-factorization formula driven by a BFKL gluon. We explore the equivalence
of this description to a collinear-factorization approach in which the
anomalous dimensions and are expressed as
power series in , or to be precise where
is the moment index. In particular we confront the
collinear-factorization expansion with that extracted from the BFKL approach
with running coupling included.Comment: 11 LaTeX pages, 1 figure (uuencoded
Asymptotic properties of DVCS
We compute the deeply virtual Compton scattering (DVCS) amplitude for forward
and backward scattering in the asymptotic limit. We make use of the Regge
calculus to resum important logarithmic contributions that are beyond those
included by the DGLAP evolution. We find a power-like behavior for the forward
DVCS amplitude.Comment: 3 pages, LaTeX, 3 figures. To be published in the proceedings of 7th
International Workshop on Deep Inelastic Scattering and QCD (DIS 99),
Zeuthen, Germany, 19-23 Apr 199
Inclusive production of meson in proton-proton collisions at BNL RHIC
Inclusive cross sections for production in proton-proton collisions
were calculated in the -factorization approach for the RHIC energy.
Several mechanisms were considered, including direct color-singlet mechanism,
radiative decays of mesons, decays of , open-charm associated
production of as well as weak decays of B mesons. Different
unintegrated gluon distributions from the literature were used. We find that
radiative decays and direct color-singlet contributions constitute the
dominant mechanism of production. These process cannot be consistently
treated within collinear-factorization approach. The results are compared with
recent RHIC data. The new precise data at small transverse momenta impose
stringent constraints on UGDFs. Some UGDFs are inconsistent with the new data.
The Kwieci\'nski UGDFs give the best description of the data. In order to
verify the mechanism suggested here we propose -- jet correlation
measurement and an independent measurement of meson production in
and/or decay channels. Finally, we address the issue of
\J spin alignment.Comment: 26 pages, 20 figures, the text was slightly modified, the title was
modified, more discussion was added, one figure was removed, one was adde
QCD running coupling effects for the non-singlet structure function at small x
A generalization of the leading-order DGLAP evolution at small x is performed
for the non-singlet structure function by resumming the leading-order DGLAP
anomalous dimension to all orders in the QCD coupling. Explicit expressions are
obtained for the non-singlet structure function of the deep inelastic
scattering, taking into account both the double-logarithmic and the
single-logarithmic contributions, including the running alpha_s effects. It is
shown that when these contributions are included, the asymptotic small-x
behaviour is power-like, with an exponent of about 0.4.Comment: Latex, 20 pages, 7 figure
Dijet Production at HERA as a Probe of BFKL Dynamics
We calculate the rate for the deep-inelastic electroproduction of dijets at
HERA. We study the weakening of the azimuthal (back-to-back) correlation
between the jets, as decreases, to see whether it can be used to identify
BFKL dynamics from conventional fixed-order QCD effects. We show how this may
give information on the transverse momentum ( dependence of the gluon
distribution of the proton.Comment: 7 pages (LaTeX) + 4 pages of figures appended in the end of the file
as a uuencoded postscript file, Durham DTP/94/56, CERN-TH.7357/9
Central exclusive production of scalar \chi_c meson at the Tevatron, RHIC and LHC energies
We calculate several differential distributions for exclusive double
diffractive production in proton-antiproton collisions at the
Tevatron and in proton-proton collisions at RHIC and LHC in terms of
unintegrated gluon distributions (UGDFs) within the -factorisation
approach. The uncertainties of the Khoze-Martin-Ryskin approach are discussed
in detail. The transition vertex is calculated as
a function of gluon virtualities applying the standard pNRQCD technique. The
off-shell effects are discussed and quantified. They lead to a reduction of the
cross section by a factor 2--5, depending on the position in the phase space
and UGDFs. Different models of UGDFs are used and the results are shown and
discussed. The cross section for diffractive component depends strongly on
UGDFs. We calculate also the differential distributions for the fusion mechanism. The integrated cross section for
photon-photon fusion is much smaller than that of diffractive origin. The two
components have very different dependence on momentum transfers in
the nucleon lines as well as azimuthal-angle correlations between both outgoing
nucleons.Comment: 34 pages, 23 figures, 2 table
Physics at Low x
The QCD expectations concerning the deep inelastic lepton - hadron scattering
at low and their phenomenological implications for HERA are summarised.
Theoretical predictions for the structure function based on the
leading log resummation are presented and compared with the results
obtained from the Altarelli-Parisi equations. Theoretical predictions are
confronted with the recent data from HERA. The role of studying the final
states in deep inelastic scattering for revealing the dynamics at low is
emphasised and some dedicated measurements like deep inelastic plus jet events,
transverse energy flow and dijet production in deep inelastic scattering are
discussed.Comment: 16 pages, 8 figures, review talk presented at the Workshop "QCD94",
7-13 July 1994, Montpellier, France (to appear in the Proceedings of the
Workshop), Krak\'ow INP report N0 1681/PH, hard copies of the figures
available on request from the author at [email protected]
Intercepts of the non-singlet structure functions
Infrared evolution equations for small- behaviour of the non-singlet
structure functions and are obtained and solved in the
next-to-leading approximation, to all orders in , and including
running effects. The intercepts of these structure functions, i.e.
the exponents of the power-like small- behaviour, are calculated. A detailed
comparison with the leading logarithmic approximation (LLA) and DGLAP is made.
We explain why the LLA predictions for the small- dependence of the
structure functions may be more reliable than the prediction for the
dependence in the range of explored at HERA.Comment: 26 pages, LaTeX, 5 Postscript figure
THE GLUON DISTRIBUTION AT SMALL x OBTAINED FROM A UNIFIED EVOLUTION EQUATION.
We solve a unified integral equation to obtain the and
dependence of the gluon distribution of a proton in the small regime; where
and are the longitudinal momentum fraction and the transverse
momentum of the gluon probed at a scale . The equation generates a gluon
with a steep behaviour, with , and a
distribution which broadens as decreases. We compare our solutions with, on
the one hand, those that we obtain using the double-leading-logarithm
approximation to Altarelli-Parisi evolution and, on the other hand, to those
that we determine from the BFKL equation.Comment: LaTeX file with 10 postscript figures (uuencoded
Associated Jet Production at HERA
We compare the BFKL prediction for the associated production of forward jets
at HERA with fixed-order matrix element calculations taking into account the
kinematical cuts imposed by experimental conditions. Comparison with H1 data of
the 1993 run favours the BFKL prediction. As a further signal of BFKL dynamics,
we propose to look for the azimuthal dependence of the forward jets.Comment: 11 pages, latex & Figures appended as uuencoded fil