Is the polarized antiquark sea in the nucleon flavor symmetric?

Abstract

We show that the model which naturally explains theū =d asymmetry in the nucleon and is in quantitative agreement with the Gottfried sum rule data, also predicts that in the proton ∆ū > 0 > ∆s > ∆d and ∆ū−∆d >d−ū > 0.At the input scale, these results can be derived even analytically. Thus the violation of the flavor symmetry is more serious in the polarized case than in the unpolarized case. In contrast, many recent analyses of the polarized data have made a simplifying assumption that all the three ∆q's have the same sign and magnitude. We point out the need to redo these analyses, allowing for the alternate scenario as described above. We present predictions of the model for the W − asymmetry in polarized pp scattering, which can be tested at RHIC; these are quite different from those available in the literature.PACS numbers: 14.20. Dh, 13.60.Hb, 13.88.+e Keywords: polarized deep inelastic scattering, polarized pp collisions, polarized parton densities, antiquark flavor asymmetry, spin asymmetries, statistical model of the nucleon 1

Nuclear EMC effect in a statistical model

“…with the upper sign for fermions (quarks, anti-quarks), and nether sign for bosons (gluons); g f is the degree of color-spin degeneracy, which is 6 for quark (anti-quark) and 16 for gluon; µ f is the corresponding chemical potential, while for anti-quark µ q = −µ q , and for gluon µ g = 0; x is the light-front momentum fraction of the nucleon carried by the specific parton; M is the mass of the nucleon, and the value is taken as 938.27 MeV; and Li 2 (z) is the polylogarithm function, defined as Li 2 (z) = ∞ k=1 z k /k 2 . Note that the analytic expression above is different from those attained in the previous statistical models [31,32,33,34,35,36,37,38,39,40,41,42].…”

“…x is the light-front momentum fraction of the nucleon carried by the specific parton; M is the mass of the nucleon, and the value is taken as 938.27 MeV; and Li 2 (z) is the polylogarithm function, defined as Li 2 (z) = ∞ k=1 z k /k 2 . Note that the analytic expression above is different from those attained in the previous statistical models [31,32,33,34,35,36,37,38,39,40,41,42].…”

“…We assume that the nucleon is a thermal system in equilibrium, made up of free partons (quarks, anti-quarks, and gluons), and the quarks and antiquarks satisfy the Fermi-Dirac distribution while the gluons obey the Bose-Einstein distribution. Instead of boosting the distribution functions to the IMF [34,35,36,37,38,39], we transform them in terms of light-front kinematic variables in the nucleon rest frame, and get x-dependent PDFs analytically [63] f…”

“…On the other hand, due to the complicated non-perturbative effect, it is still difficult to calculate the parton distribution functions (PDFs) of the free nucleon absolutely from the first principle theory of the quantum chromodynamics (QCD) at present. Various models according to the spirit of QCD have been brought forward, therein statistical ones, providing intuitive appeal and physical simplicity, have made amazing success [29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49 Actually, as can be speculated, with partons bound in the wee volume of the nucleon, not only the dynamic, but also the statistical properties, for example, the Pauli exclusion principle, should have important effect on PDFs. Angelini and Pazzi [29,30], as pioneers, found that the nucleon valence quark distribution has a thermodynamical behavior for x > 0.1 with the temperature decreasing for different Q 2 .…”

“…Cleymans and Thews [31,32,33] explored a statistical way to generate compatible PDFs. Mac and Ugaz [34] incorporated first order QCD correction, and afterwards Bhalerao et al [35,36,37,38,39] introduced finite-size correction; they both referred to the infinite-momentum frame (IMF). Devanathan et al [40,41,42] proposed a thermodynamical bag model which evolves as a function of x, and the structure functions they got have correct asymptotic behavior; in addition, they parametrized on T and exhibited the scaling behavior.…”