82 research outputs found
A statistical approach for polarized parton distributions
A global next-to-leading order QCD analysis of unpolarized and polarized
deep-inelastic scattering data is performed with parton distributions
constructed in a statistical physical picture of the nucleon. The chiral
properties of QCD lead to strong relations between quarks and antiquarks
distributions and the importance of the Pauli exclusion principle is also
emphasized. We obtain a good description, in a broad range of and , of
all measured structure functions in terms of very few free parameters. We
stress the fact that at RHIC-BNL the ratio of the unpolarized cross sections
for the production of and in collisions, will directly probe
the behavior of the ratio for , a definite
and important test for the statistical model. Finally, we give specific
predictions for various helicity asymmetries for the production in
collisions at high energies, which will be measured with forthcoming
experiments at RHIC-BNL and are sensitive tests of the statistical model for
and .Comment: 49 pages, 27 eps figure
Impact-picture predictions for the total cross section at LEP
We show that the rising total cross section recently observed by the L3 and OPAL Collaborations at LEP are fully
consistent with the impact-picture for high-energy scattering. The impact
picture is then used to predict this total cross section at higher energies.
These experimental results confirm once more the success of the theoretical
approach, which predicted for the first time, nearly thirty years ago, the
universal increase of total cross sections at high energies.Comment: 5 pages, Latex, 1 figure. Revised versio
Do we understand the single-spin asymmetry for inclusive production in pp collisions?
The cross section data for inclusive production in collisions is
considered in a rather broad kinematic region in energy , Feynman
variable and transverse momentum . The analysis of these data is
done in the perturbative QCD framework at the next-to-leading order. We find
that they cannot be correctly described in the entire kinematic domain and this
leads us to conclude that the single-spin asymmetry, for this process,
observed several years ago at FNAL by the experiment E704 and the recent result
obtained at BNL-RHIC by STAR, are two different phenomena. This suggests that
STAR data probes a genuine leading-twist QCD single-spin asymmetry for the
first time and finds a large effect.Comment: text modified, version to be published in Eur. Phys. J. C, 6 pages, 5
figure
The evolution of Soffer inequality
DGLAP evolution equations may be presented in a form completely analogous to
the Boltzmann equation. This provides a natural proof of the positivity of the
spin-dependent parton distributions, provided the initial distributions at
are also positive. In addition, the evolution to may
violate positivity, providing therefore a 'time arrow'. The positivity
condition is just for for all
types of partons, while the prescription and terms containing
do not affect positivity. This method allows one to complete
immediately the existing proof of Soffer inequality at leading and
next-to-leading order.Comment: 11 pages, LateX, eps sty, 3 eps figure
Polarized Quarks, Gluons and Sea in Nucleon Structure Functions
We perform a NLO analysis of polarized deep inelastic scattering data to test
two different solutions to the so called spin crisis: one of them based on the
axial gluon anomaly and consistent with the Bjorken sum rule and another one,
where the defects in the spin sum rules and in the Gottfried sum rule are
related. In this case a defect is also expected for the Bjorken sum rule. The
first solution is slightly favoured by the SLAC E154 results, but both options
seem to be consistent with the CERN SMC data.Comment: 19 pages, LateX, 6 figures. Figures included in the tex
Proton-helium elastic scattering: a possible high-energy polarimeter at RHIC-BNL
We examine a suggestion to use elastic scattering, as an
absolute polarimeter for high-energy polarized proton beams, by means of a
Coulomb-Nuclear Interference effect for the single-spin asymmetry ,
around the diffractive minimum of the differential cross section . Although this reaction has a fairly simple dynamical structure, our
theoretical uncertainties and the present experimental inaccuracy of the
differential cross section in this region, allows one to generate dramatic
effects for , which will be discussed.Comment: 8 pages, Latex, 4 figure
WHY THE REAL PART OF THE PROTON-PROTON FORWARD SCATTERING AMPLITUDE SHOULD BE MEASURED AT THE LHC
4p, 2figs, Contribution to EDS2005, Blois May 2005For the energy of 14 TeV, to be reached at the Large Hadron Collider (LHC), we have had for some time accurate predictions for both the real and imaginary parts of the forward proton-proton elastic scattering amplitude. LHC is now scheduled to start operating in two years, and it is timely to discuss some of the important consequences of the measurements of both the total cross-section and the ratio of the real to the imaginary part. We stress the importance of measuring the real part of the proton-proton forward scattering amplitude at LHC, because a deviation from existing theoretical predictions could be a strong sign for new physics
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