Asymmetries of quark sea in nucleon

Harleen Dahiya

doi:10.1051/epjconf/20147302004

Abstract

The effects of in determining the flavor structure of the octet baryons have been investigated in the chiral constituent quark model. The chiral constituent quark model is able to qualitatively generate the requisite amount of quark sea and is also known to provide a satisfactory explanation of the spin and related issues in the nonperturbative regime. The phenomenological implications of the quark sea asymmetries in the nucleon have been investigated to understand the importance of quark sea at lower values of the Bjorken scaling variable. After the first direct evidence for the point-like constituents in the nucleon, identified as the valence quarks with spin-1/2 in the naive constituent quark model (NQM) (1-3), a lot of experiments have been conducted to probe the structure of the in the deep inelastic scattering (DIS) experiments. Surprisingly, the DIS results in the early 80's (4) indicated that the valence quarks of the carry only about 30% of its spin and is referred to as the proton spin crisis in the NQM. These results provided the first evidence for the being composed of three valence quarks surrounded by an indistinct sea of quark-antiquark pairs (henceforth referred to as the sea). In the present day, the study of the composition of hadrons can be said to be primarily the study of the quark sea and gluons and is considered as one of the active areas in hadronic physics. The conventional expectation that the quark sea perhaps can be obtained through the perturbative production of the quark-antiquark pairs by gluons produces nearly equal numbers of ¯ u and ¯ d. Until early 90's a symmetric sea w.r.t. ¯ u and ¯ d was assumed, however, the famous New Muon Collaboration in 1991 (5) established the quark sea asymmetry of the unpolarized quarks in the case of nucleon by measuring ¯ d − ¯ u giving first clear evidence for the nonperturbative origin of the quark sea. This was later confirmed by the Drell-Yan experiments (6) which measured a large quark sea asymmetry ratio ¯ d/¯ u reminding us that the study of the quark sea is intrinsically a nonperturbative phenomena and it is still a big challenge to perform these calculations from the first principles of QCD. The chiral constituent quark model (CQM) (7) can yield an adequate description of the quark sea generation through the chiral fluctuations. The basic idea is based on the possibility that chiral symmetry breaking takes place at a distance scale much smaller than the confinement scale. In this region, the effective degrees of freedom are the valence quarks and the internal Goldstone bosons (GBs) which are coupled to the valence quarks (8-10) allowing a simple and intuitive method to investigate

Highlights

After the first direct evidence for the point-like constituents in the nucleon, identified as the valence quarks with spin-1/2 in the naive constituent quark model (NQM) [1,2,3], a lot of experiments have been conducted to probe the structure of the proton in the deep inelastic scattering (DIS) experiments
The DIS results in the early 80’s [4] indicated that the valence quarks of the proton carry only about 30% of its spin and is referred to as the “proton spin crisis” in the NQM. These results provided the first evidence for the proton being composed of three valence quarks surrounded by an indistinct sea of quark-antiquark pairs
Until early 90’s a symmetric sea w.r.t. uand dwas assumed, the famous New Muon Collaboration in 1991 [5] established the quark sea asymmetry of the unpolarized quarks in the case of nucleon by measuring d − ugiving first clear evidence for the nonperturbative origin of the quark sea. This was later confirmed by the Drell-Yan experiments [6] which measured a large quark sea asymmetry ratio d /ureminding us that the study of the quark sea is intrinsically a nonperturbative phenomena and it is still a big challenge to perform these calculations from the first principles of QCD

Summary

Introduction

After the first direct evidence for the point-like constituents in the nucleon, identified as the valence quarks with spin-1/2 in the naive constituent quark model (NQM) [1,2,3], a lot of experiments have been conducted to probe the structure of the proton in the deep inelastic scattering (DIS) experiments. In the case of quark distribution functions, the latest developments by the NuSea (E866) [11] and HERMES [12] to determine the variation of the seaantiquark ratio d (x)/u (x) and the difference d (x)-u (x) with Bjorken scaling variable x have renewed considerable interest in the quark sea asymmetries. There has been substantial theoretical progress to take into account the effects of quark sea in determining the flavor structure of the baryons and the question of sea asymmetry has been investigated by several authors using various phenomenological models [13,14,15,16,17,18,19].

Results

Conclusion