329 research outputs found

### Determination of the forward slope in $p~p$ and $\bar p~p$ elastic scattering up to LHC energy

In the analysis of experimental data on $p p$ (or $\bar p p$) elastic
differential cross section it is customary to define an average forward slope
$b$ in the form $\exp{(-b|t|)}$, where $t$ is the momentum transfer. Taking as
working example the results of experiments at Tevatron and SPS, we will show
with the help of the impact picture approach, that this simplifying assumption
hides interesting information on the complex non-flip scattering amplitude, and
that the slope $b$ is not a constant. We investigate the variation of this
slope parameter, including a model-independent way to extract this information
from an accurate measurement of the elastic differential cross section. An
extension of our results to the LHC energy domain is presented in view of
future experiments.Comment: 12 pages, 6 figures, to appear in EPJ

### 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 $x$ and $Q^2$, 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 $W^+$ and $W^-$ in $pp$ collisions, will directly probe
the behavior of the $\bar d(x) / \bar u(x)$ ratio for $x \geq 0.2$, a definite
and important test for the statistical model. Finally, we give specific
predictions for various helicity asymmetries for the $W^{\pm}, Z$ production in
$pp$ collisions at high energies, which will be measured with forthcoming
experiments at RHIC-BNL and are sensitive tests of the statistical model for
$\Delta \bar u(x)$ and $\Delta \bar d(x)$.Comment: 49 pages, 27 eps figure

### Impact-picture predictions for the $\gamma\gamma$ total cross section at LEP

We show that the rising total cross section $\sigma(\gamma\gamma \to
hadrons)$ 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

### The statistical parton distributions: status and prospects

New experimental results on polarized structure functions, cross sections for
$e^{\pm}p$ neutral and charge current reactions and $\nu$ ($\bar{\nu}$) charge
current on isoscalar targets are compared with predictions using the
statistical parton distributions, which were previously determined. New data on
cross sections for Drell-Yan processes, single jet in $p\bar{p}$ collisions and
inclusive $\pi^0$ production in $pp$ collisions are also compared with
predictions from this theoretical approach. The good agreement which we find
with all these tests against experiment, strenghtens our opinion on the
relevance of the role of quantum statistics for parton distributions. We will
also discuss the prospects of this physical framework.Comment: 34 pages, 23 figures, references and figures adde

### Do we understand the single-spin asymmetry for $pi^0$ inclusive production in pp collisions?

The cross section data for $\pi^0$ inclusive production in $pp$ collisions is
considered in a rather broad kinematic region in energy $\sqrt{s}$, Feynman
variable $x_F$ and transverse momentum $p_T$. 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, $A_N$ 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

### Further experimental tests for simple relations between unpolarized and polarized quark parton distributions

Some simple relations between unpolarized and polarized quark parton
distributions have direct experimental consequences which will be presented
here. In particular, we will see that it is possible to relate the deep
inelastic structure functions $F_2$ and $g_1$, both for proton and deuteron, in
fair agreement with experimental data.Comment: 5 pages, in Latex, 3 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

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