The flavor asymmetry in the polarized proton sea

Abstract

We perform a careful study on the effect of the Pauli blocking to the light polarized antiquark structure of the proton sea. We develop the formal expressions for the polarized antiquark distributions, highlighting the role played by quark statistics and the vacuum structure. The ratio involving the polarized antiquarks is calculated. In particular, it is found that ∆d(x)/∆u(x) should be negative and x independent.Spin physics has atracted a lot of attention in the last 15 years, both experimentally and theoretically. Since the first precise results on the proton longitudinal polarized structure function was released, in the late 1980's, we have learned a great deal about how the quarks and gluons combine to produce the observed spin of the proton [1]. However, we are still uncertain abou the correct size of the gluon distribution as well as the decomposition of the quark contribution to the total spin in terms of its quark and antiquark parts. COM-PASS at CERN is starting to measure the polarized gluon distribution directly using a polarized muon beam. On the quark side, the semi-inclusive program of HERMES has released some recent results for the quark polarizations of u, u, d, d, and s + s [2]. There is a good agreement between their data and parametrizations for the valence distributions in NLO QCD. However, the antiquark distributions are still plagued with sizeable statistical uncertainties. In particular, it is not possible to determine weather the light antiquarks are flavor asymmetric, as observed in unpolarized scattering, in the case of polarized distributions.There are, on the other hand, a strong theoretical motivation for the asymmetry to be present also in the polarized sector, and this work is devoted to advocate what should be the most compelling mechanism: the fundamental role played by the quark statistics in both the polarized and unpolarized antiquark distributions. This work is a more detailed version of some previously published results [3] on this problem.In order to isolate the Pauli blocking effects to the sea structure of the proton, we work out the formal definition of the antiquark distributions to a point where some actual predictions can be made without the introduction of a number of model parameters. From this point, we are able to study to what extent Pauli Blocking is a correction or is the main phenomenon behind the sea asymmetry of the light quarks.We start with the formal definition of the polarized antiquark distribution [4]:with x > 0. To calculate Eq. (1), we remember that:with the field operators expanded in terms of free plane waves:Using Eqs. (2) and (3) in Eq.(1), we get: