190 research outputs found
Unintegrated parton distributions and inclusive jet production at HERA
We describe how unintegrated parton distributions can be calculated from
conventional integrated distributions. We extend and improve the 'last-step'
evolution approach, and explain why doubly-unintegrated parton distributions
are necessary. We generalise k_t-factorisation to (z,k_t)-factorisation. We
apply the formalism to inclusive jet production in deep-inelastic scattering,
mainly at leading-order, but we also study the extension to next-to-leading
order. We compare the predictions with recent HERA data.Comment: 32 pages, 11 figures. Version to appear in Eur. Phys. J.
The unintegrated gluon distribution from the CCFM equation
The gluon distribution f(x, k_t^2,mu^2), unintegrated over the transverse
momentum k_t of the gluon, satisfies the angular-ordered CCFM equation which
interlocks the dependence on the scale k_t with the scale \mu of the probe. We
show how, to leading logarithmic accuracy, the equation can be simplified to a
single scale problem. In particular we demonstrate how to determine the
two-scale unintegrated distribution f(x,k_t^2,mu^2) from knowledge of the
integrated gluon obtained from a unified scheme embodying both BFKL and DGLAP
evolution.Comment: 16 pages LaTeX, 3 eps figure
Diffractive gamma-gamma production at hadron colliders
We compute the cross section for exclusive double-diffractive gamma-gamma
production at the Tevatron, , and
the LHC. We evaluate both the gluon-gluon and quark-antiquark t-channel
exchange contributions to the process. The observation of exclusive gamma-gamma
production at the Tevatron will provide a check on the model predictions, and
offer an opportunity to confirm the expectations for exclusive
double-diffractive Higgs production at the LHC.Comment: 16 pages, 7 figure
NLO prescription for unintegrated parton distributions
We show how parton distributions unintegrated over the parton transverse
momentum, k_t, may be generated, at NLO accuracy, from the known integrated
(DGLAP-evolved) parton densities determined from global data analyses. A few
numerical examples are given, which demonstrate that sufficient accuracy is
obtained by keeping only the LO splitting functions together with the NLO
integrated parton densities. However, it is important to keep the precise
kinematics of the process, by taking the scale to be the virtuality rather than
the transverse momentum, in order to be consistent with the calculation of the
NLO splitting functions.Comment: 20 pages, 8 figures. v2: version to appear in Eur. Phys. J.
Q^2 dependence of diffractive vector meson electroproduction
We give a general formula for the cross section for diffractive vector meson
electroproduction, gamma^* p -> Vp. We first calculate diffractive qqbar
production, and then use parton-hadron duality by projecting out the J^P = 1^-
state in the appropriate mass interval. We compare the Q^2 dependence of the
cross section for the diffractive production of rho and J/psi mesons with
recent HERA data. We include the characteristic Q^2 dependence associated with
the use of the skewed gluon distribution. We give predictions for
sigma_L/sigma_T for both rho and J/psi production.Comment: 15 pages, LaTeX, including five PostScript figure
Solution of the Kwiecinski evolution equations for unintegrated parton distributions using the Mellin transform
The Kwiecinski equations for the QCD evolution of the unintegrated parton
distributions in the transverse-coordinate space (b) are analyzed with the help
of the Mellin-transform method. The equations are solved numerically in the
general case, as well as in a small-b expansion which converges fast for b
Lambda_QCD sufficiently small. We also discuss the asymptotic limit of large bQ
and show that the distributions generated by the evolution decrease with b
according to a power law. Numerical results are presented for the pion
distributions with a simple valence-like initial condition at the low scale,
following from chiral large-N_c quark models. We use two models: the Spectral
Quark Model and the Nambu--Jona-Lasinio model. Formal aspects of the equations,
such as the analytic form of the b-dependent anomalous dimensions, their
analytic structure, as well as the limits of unintegrated parton densities at x
-> 0, x -> 1, and at large b, are discussed in detail. The effect of spreading
of the transverse momentum with the increasing scale is confirmed, with
growing asymptotically as Q^2 alpha(Q^2). Approximate formulas for
for each parton species is given, which may be used in practical
applications.Comment: 18 pages, 6 figures, RevTe
An application of transverse-momentum-dependent evolution equations in QCD
The properties and behaviour of the solutions of the recently obtained
-dependent evolution equations are investigated. When used to reproduce
transverse momentum spectra of hadrons in Semi-Inclusive DIS, an encouraging
agreement with data is found. The present analysis also supports at the
phenomenological level the factorization properties of the Semi-Inclusive DIS
cross-sections in terms of -dependent distributions. Further improvements
and possible developments of the proposed evolution equations are envisaged.Comment: 6 pages, page format correcte
Prompt photon and associated heavy quark production at hadron colliders with kt-factorization
In the framework of the kt-factorization approach, the production of prompt
photons in association with a heavy (charm or beauty) quarks at high energies
is studied. The consideration is based on the O(\alpha \alpha_s^2) off-shell
amplitudes of gluon-gluon fusion and quark-(anti)quark interaction
subprocesses. The unintegrated parton densities in a proton are determined
using the Kimber-Martin-Ryskin prescription. The analysis covers the total and
differential cross sections and extends to specific angular correlations
between the produced prompt photons and muons originating from the semileptonic
decays of associated heavy quarks. Theoretical uncertainties of our evaluations
are studied and comparison with the results of standard NLO pQCD calculations
is performed. Our numerical predictions are compared with the recent
experimental data taken by the D0 and CDF collaborations at the Tevatron.
Finally, we extend our results to LHC energies.Comment: 14 pages, 10 figure
Double parton scatterings in b-quark pairs production at the LHC
A sizable rate of events where two pairs of b-quarks are produced
contemporarily is foreseen at the CERN LHC, as a consequence of the large
parton luminosity. At very high energies both single and the double parton
scatterings contribute to the process, the latter mechanisms, although power
suppressed, giving the dominant contribution to the integrated cross section.Comment: 17 pages, 6 figure
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