Determination of the forward slope in p pp~p and pˉ p\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 γγ\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 pi0pi^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