42 research outputs found
Heavy Quark Production in Parton Model and in QCD
The cross sections of heavy quark production in collision and for their
photo- and electroproduction are calculated in the framework of QCD. The
virtual nature of the interacting gluons as well as their transverse motion and
different polarizations are taken into account. The obtained cross sections
exhibit more rapid growth with the initial energy than the parton model
predictions and the distributions of produced heavy quarks are more
smooth.Comment: 12 pages, LaTeX, 10 uuencoded-compressed-tar fig
Treatment of heavy quarks in QCD
We show that to correctly describe the effects of the heavy-quark mass, m_h,
in DGLAP evolution, it is necessary to work in the so-called `physical' scheme.
In this way, we automatically obtain a smooth transition through the
heavy-quark thresholds. Moreover, we show that to obtain NLO accuracy, it is
sufficient to account for the heavy-quark mass, m_h, just in the LO (one-loop)
splitting function. The use of the MS-bar factorisation scheme is not
appropriate, since at NLO we deal with a mixture of quarks and gluon (that is,
the mass of the heavy parton is not well-defined). The formulae for the
explicit m_h dependence of the splitting functions, and for alpha_s, are
presented.Comment: 14 pages, 3 figures, references updated, version to be published in
EPJ
Diffractive parton distributions from perturbative QCD
The asymptotic collinear factorisation theorem, which holds for diffractive
deep-inelastic scattering, has important modifications in the sub-asymptotic
HERA regime. We use perturbative QCD to quantify these modifications. The
diffractive parton distributions are shown to satisfy an inhomogeneous
evolution equation. We emphasise that it is necessary to include both the
gluonic and sea-quark t-channel components of the perturbative Pomeron. The
corresponding Pomeron-to-parton splitting functions are derived in the
Appendix.Comment: 34 pages, 13 figures. Version published in Eur. Phys. J.
A QCD analysis of diffractive deep-inelastic scattering data
We perform a novel type of analysis of diffractive deep-inelastic scattering
data, in which the input parton distributions of the Pomeron are parameterised
using the perturbative QCD expressions. In particular, we treat individually
the components of the Pomeron of different size. We are able to describe
simultaneously both the recent ZEUS and H1 diffractive data. In addition to the
usual two-gluon model for the perturbative Pomeron, we allow for the
possibility that it may be made from two sea quarks.Comment: 13 pages, 5 figures. Version published in Eur. Phys. J.
Comparison of -Factorization Approach and QCD Parton Model for Charm and Beauty Hadroproduction
We compare the numerical predictions for heavy quark production in high
energy hadron collisions of the conventional QCD parton model and the
-factorization approach (semihard theory). The total production cross
sections, one-particle rapidity and distributions as well as two-particle
correlations are considered. The difference in the predictions of the two
approaches is not very large, while the shapes of the distributions are
slightly different.Comment: 16 pages, LaTeX, + 16 PostScript figure
Heavy Quark Hadroproduction in -Factorization Approach with Unintegrated Gluon Distributions
We consider the processes of compare the heavy quark production using the
unintegrated gluon distributions. The numerical predictions for high energy
nucleon-nucleon and photon-nucleon collisions of the -factorization
approach (semihard theory) are compared with the experimental data from
Tevatron-collider and HERA. The total production cross sections and
distributions are considered and they are in reasonable agreement with the data
for rather value of QCD scale.Comment: 21 pages, 10 figures, references adde