Can sea quark asymmetry shed light on the orbital angular momentum of the proton?

Abstract

A striking prediction of several extensions of the constituent quark model, including the unquenched quark model, the pion cloud model and the chiral quark model, is a proportionality relationship between the quark sea asymmetry and the orbital angular momentum of the proton. We investigate to which extent a relationship of this kind is corroborated by the experiment, through a systematic comparison between expectations based on models and predictions obtained from a global analysis of hard-scattering data in perturbative Quantum Chromodynamics. We find that the data allows the angular momentum of the proton to be proportional to its sea asymmetry, though with a rather large range of the optimal values of the proportionality coefficient. Typical values do not enable us to discriminate among expectations based on different models. In order to make our comparison conclusive, the extrapolation uncertainties on the proportionality coefficient should be reduced, hopefully by means of accurate measurements in the region of small proton momentum fractions, where the data is currently lacking. Nevertheless, the unquenched quark model predicts that quarks account for a proton spin fraction much larger than that accepted by the conventional wisdom. We explicitly demonstrate that such a discrepancy can be reabsorbed in the unknown extrapolation region, without affecting the description of current data, by imposing the unquenched quark model expectation as a boundary condition in the analysis of the data itself. We delineate how the experimental programs at current and future facilities may shed light on the region of small momentum fractions.

arXiv comment7 pages, 3 figures, 3 tables

References in corpus (38)

• Parton distributions for the LHC Run II
• A Large Hadron Electron Collider at CERN: Report on the Physics and Design Concepts for Machine and Detector
• Improved Measurement of the $\bar{d}/\bar{u}$ Asymmetry in the Nucleon Sea
• Measurements of the Proton and Deuteron Spin Structure Functions g1 and g2
• The angular momentum controversy: What's it all about and does it matter?
• Precise determination of the spin structure function ${\mathbf{g}}_1$ of the proton, deuteron and neutron
• A first unbiased global determination of polarized PDFs and their uncertainties
• Precision Determination of the Neutron Spin Structure Function g1n
• Evidence for polarization of gluons in the proton
• Measurement of the Neutron Spin Structure Function $g_1^n$ with a Polarized ^3He Target
• Deep Inelastic Scattering of Polarized Electrons by Polarized ${}^3$He and the Study of the Neutron Spin Structure
• Measurements of the $Q^2$-Dependence of the Proton and Neutron Spin Structure Functions g1p and g1n
• Flavor Asymmetry of Antiquark Distributions in the Nucleon
• Measurement of inclusive jet and dijet production in pp collisions at sqrt(s) = 7 TeV using the ATLAS detector
• The Flavor Asymmetry of the Light Quark Sea from Semi-inclusive Deep-inelastic Scattering
• The Spin-dependent Structure Function of the Proton g_1^p and a Test of the Bjorken Sum Rule
• Flavor Asymmetry of Light Quarks in the Nucleon Sea
• Progress in the Determination of the Partonic Structure of the Proton
• Measurement of the lepton charge asymmetry in inclusive W production in pp collisions at sqrt(s) = 7 TeV
• The Spin Structure Function $g_1^{\mathrm{p}}$ of the Proton and a Test of the Bjorken Sum Rule
• Flavor and Spin Contents of the Nucleon in the Quark Model with Chiral Symmetry
• Inclusive $W$ and $Z$ production in the forward region at $\sqrt{s}=7$ TeV
• Direct Measurement of the $W$ Production Charge Asymmetry in $\ppbar$ Collisions at $\sqrt{s}=1.96$ TeV
• The RHIC SPIN Program: Achievements and Future Opportunities
• Helicity Evolution at Small $x$: Flavor Singlet and Non-Singlet Observables
• Small-$x$ asymptotics of the quark helicity distribution
• Unquenched quark model for baryons: magnetic moments, spins and orbital angular momenta
• On the Interface between Perturbative and Nonperturbative QCD
• Precision measurements of $g_1$ of the proton and the deuteron with 6 GeV electrons
• Precise Determination of the Deuteron Spin Structure at Low to Moderate $Q^2$ with CLAS and Extraction of the Neutron Contribution
• Helicity Parton Distributions at a Future Electron-Ion Collider: A Quantitative Appraisal
• Unveiling the Proton Spin Decomposition at a Future Electron-Ion Collider
• Precision Measurements of $A_1^n$ in the Deep Inelastic Regime
• Polarized Parton Distributions at an Electron-Ion Collider
• Unbiased determination of polarized parton distributions and their uncertainties
• Orbital Angular Momentum in the Nucleon
• Unbiased polarized PDFs upgraded with new inclusive DIS data
• Achievements and open issues in the determination of polarized parton distribution functions

Cited by in corpus (2)

• Small-$x$ Asymptotics of the Quark Helicity Distribution: Analytic Results
• Parton distribution functions with QED corrections in the valon model