A statistical approach for polarized parton distributions

Abstract

A global next-to-leading order QCD analysis of unpolarized and polarized deepinelastic 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 d(x)/u(x) ratio for x ≥ 0.2, a definite and important test for the statistical model. Finally, we give specific predictions for various helicity asymmetries for the W ± , 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 ∆u (x) and ∆d(x).

Constraining the Sea Quark Distributions Through W$^\pm$ Cross Section Ratio Measurements at STAR

“…As a result no background corrections have been made to the Z candidate measurements. [17,18] and theory frame works [19,20]. The σ f id W ± /σ f id Z cross section ratio is shown in Fig.…”

On the shape of the d¯−u¯ asymmetry

“…Of course, additional mechanisms beyond those associated with chiral symmetry breaking, such as those based on the Pauli exclusion principle [16][17][18][69][70][71], may play a role in generating some of the asymmetry. Whether and to what extent such mechanisms are important phenomenologically may be revealed with the upcoming Drell-Yan data [23,77].…”

Spin physics through unpolarized processes

“…The latter two distributions are spin-dependent and are essential observables to encode the spin structure of the polarized nucleon. During the past two decades, detailed knowledge on the quark helicity distribution has been obtained from different model calculations [4][5][6], as well as from dedicated experimental measurements, which shed light on the parametrizations of g 1 (x) [7][8][9][10][11]. Although it is more difficult to probe the quark transversity distribution due to its chiral-odd nature, researchers have started gaining some basic information of this distribution by taking advantage of the semi-inclusive deeply inelastic scattering (SIDIS) process [12,13].…”