12 research outputs found
Nonlinear corrections to the DGLAP equations; looking for the saturation limits
The effects of the first nonlinear corrections to the DGLAP equations are studied in light of the HERA data. Saturation limits are determined in the DGLAP+GLRMQ approach for the free proton and for the Pb nucleus.The effects of the first nonlinear corrections to the DGLAP equations are studied in light of the HERA data. Saturation limits are determined in the DGLAP+GLRMQ approach for the free proton and for the Pb nucleus.The effects of the first nonlinear corrections to the DGLAP equations are studied in light of the HERA data. Saturation limits are determined in the DGLAP+GLRMQ approach for the free proton and for the Pb nucleus
Nuclear Parton Distributions - a DGLAP Analysis
Nuclear parton distributions are studied within a framework of
the DGLAP evolution. Measurements of in deep inelastic
collisions, and Drell--Yan dilepton cross sections measured in collisions
are used as constraints. Also conservation of momentum and baryon number is
required. It is shown that the calculated evolution of agrees very well with the recent NMC data, and that the ratios
are only moderately sensitive to the choice of a specific modern
set of free parton distributions. For general use, we offer a numerical
parametrization of for all parton flavours in , and at
and .Comment: Talk in Quark Matter '99, 5 pages, includes 3 eps-figure
Obtaining the nuclear gluon distribution from heavy quark decays to lepton pairs in p collisions
We have studied how lepton pairs from decays of heavy-flavoured mesons
produced in p collisions can be used to determine the modifications of the
gluon distribution in the nucleus. Since heavy quark production is dominated by
the channel, the ratio of correlated lepton pair cross sections from
and decays in p and pp collisions directly reflects the
ratio . We have numerically calculated the lepton
pair cross sections from these decays in pp and p collisions at SPS, RHIC
and LHC energies. We find that ratio of the p to pp cross sections agrees
quite well with the input Thus, sufficiently accurate measurements
could be used to determine the nuclear modification of the gluon distribution
over a greater range of and than presently available, putting strong
constraints on models.Comment: 19 pages, 6 figure
Nonlinear corrections to the DGLAP equations in view of the HERA data
The effects of the first nonlinear corrections to the DGLAP evolution
equations are studied by using the recent HERA data for the structure function
of the free proton and the parton distributions from CTEQ5L and
CTEQ6L as a baseline. By requiring a good fit to the H1 data, we determine
initial parton distributions at GeV for the nonlinear scale
evolution. We show that the nonlinear corrections improve the agreement with
the data in the region of and
GeV without paying the price of obtaining a worse agreement at larger
values of and . For the gluon distribution the nonlinear effects are
found to play an increasingly important role at x\lsim 10^{-3} and
Q^2\lsim10 GeV, but rapidly vanish at larger values of and .
Consequently, contrary to CTEQ6L, the obtained gluon distribution at
GeV shows a power-like growth at small . Relative to the CTEQ6L gluons,
an enhancement up to a factor at , GeV
reduces to a negligible difference at Q^2\gsim 10 GeV.Comment: 13 pages, 5 eps-figures; revision: references added, Fig. 3 revise
Enhancement of charm quark production due to nonlinear corrections to the DGLAP equations
We have studied how parton distributions based on the inclusion of nonlinear
scale evolution and constraints from HERA data affect charm production in
collisions at center-of-mass energies of 5.5, 8.8 and 14 TeV. We find that,
while the resulting enhancement can be substantial, it is very sensitive to the
charm quark mass and the scale entering the parton densities and the strong
coupling constant.Comment: 14 pages, 5 eps-figure
Scale evolution of nuclear parton distributions
Using the NMC and E665 nuclear structure function ratios and
from deep inelastic lepton-nucleus collisions, and the E772
Drell--Yan dilepton cross sections from proton-nucleus collisions, and
incorporating baryon number and momentum sum rules, we determine nuclear parton
distributions at an initial scale . With these distributions, we study
QCD scale evolution of nuclear parton densities. The emphasis is on small
values of , especially on scale dependence of nuclear shadowing. As the main
result, we show that a consistent picture can be obtained within the leading
twist DGLAP evolution, and in particular, that the calculated dependence
of agrees very well with the recent NMC data.Comment: 26 pages, including 10 eps-figure
Recommended from our members
D-meson enhancement in pp collisions at the LHC due to nonlinear gluon evolution
When nonlinear effects on the gluon evolution are included with constraints from HERA, the gluon distribution in the free proton is enhanced at low momentum fractions, x\leq 0.01, and low scales, Q2\lsim 10 GeV2, relative to standard, DGLAP-evolved, gluon distributions. Consequently, such gluon distributions can enhance charm production in pp collisions at center of mass energy 14 TeV by up to a factor of five at midrapidity, y\sim0, and transverse momentum p_T\rightarrow0 in the most optimistic case. We show that most of this enhancement survives hadronization into D mesons. Assuming the same enhancement at leading and next-to-leading order, we show that the enhancement may be measured by D0 reconstruction in the K-pi+ decay channel with the ALICE detector
Heavy Quarks: Summary Report
The present status of the heavy-quark production theory is critically reviewed in the first contribution. The second contribution summarises the present heavy flavour data from HERA and gives an outlook of what can be expected from HERA-II. The potential of the LHC experiments for charm and beauty physics is reviewed in the 3rd contribution. Then the relevance of saturation and small-x effects to heavy quark production at HERA and at the LHC are discussed. The non-perturbative aspects of heavy-quark fragmentation and their relevance to HERA and LHC are discussed in the next contribution. Finally, a comparison of different theoretical predictions for HERA and LHC based on different approaches is presented