scholarly journals Quark and Glue Components of the Proton Spin from Lattice Calculation

2016 ◽  
Vol 40 ◽  
pp. 1660005 ◽  
Author(s):  
Keh-Fei Liu
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Ward Identity ◽  
Proton Spin ◽  
Lattice Calculation ◽  
Quark Spin ◽  
The Status ◽  
Quark Orbital Angular Momentum ◽  
Spin Crisis ◽  
Anomalous Ward Identity

The status of lattice calculations of the quark spin, the quark orbital angular momentum, the glue angular momentum and glue spin in the nucleon is summarized. The quark spin calculation is recently carried out from the anomalous Ward identity with chiral fermions and is found to be small mainly due to the large negative anomaly term which is believed to be the source of the ‘proton spin crisis’. We also present the first calculation of the glue spin at finite nucleon momenta.

WHAT WE KNOW AND DON'T KNOW ABOUT THE ORIGIN OF THE SPIN OF THE PROTON

2010 ◽  
Vol 25 (22) ◽  
pp. 4149-4162 ◽  
Author(s):  
ANTHONY W. THOMAS ◽  
ANDREW CASEY ◽  
HRAYR H. MATEVOSYAN
Keyword(s):  
Angular Momentum ◽  
Lattice Qcd ◽  
Orbital Angular Momentum ◽  
Proton Spin ◽  
Hadron Physics ◽  
Proton Structure ◽  
Tremendous Progress ◽  
Quark Orbital Angular Momentum ◽  
Modern Information ◽  
Spin Crisis

The origin of the spin of the proton is one of the most fundamental questions in modern hadron physics. Although tremendous progress has been made since the discovery of the "spin crisis" brought the issue to the fore, much remains to be understood. We carefully review what is known and, especially in the case of lattice QCD, what is not known. We also explain the importance of QCD inspired models in providing a physical picture of proton structure and the connection between those models and what is measured experimentally and on the lattice. We specifically apply these ideas to the issue of quark orbital angular momentum in the proton. We show that the Myhrer–Thomas resolution of the proton spin crisis is remarkably consistent with modern information from lattice QCD.

scholarly journals Baryons and chiral symmetry

2017 ◽  
Vol 26 (01n02) ◽  
pp. 1740016 ◽  
Author(s):  
Keh-Fei Liu
Keyword(s):  
Chiral Symmetry ◽  
Ward Identity ◽  
Effective Theory ◽  
Roper Resonance ◽  
Lattice Calculation ◽  
The Third ◽  
Quark Spin ◽  
Quark Orbital Angular Momentum ◽  
Anomalous Ward Identity

The relevance of chiral symmetry in baryons is highlighted in three examples in the nucleon spectroscopy and structure. The first one is the importance of chiral dynamics in understanding the Roper resonance. The second one is the role of chiral symmetry in the lattice calculation of [Formula: see text] term and strangeness. The third one is the role of chiral [Formula: see text] anomaly in the anomalous Ward identity in evaluating the quark spin and the quark orbital angular momentum. Finally, the chiral effective theory for baryons is discussed.

scholarly journals QUARK ORBITAL ANGULAR MOMENTUM IN THE BARYON

2001 ◽  
Vol 16 (22) ◽  
pp. 3673-3697 ◽  
Author(s):  
XIAOTONG SONG
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Orbital Motion ◽  
Magnetic Moments ◽  
Sum Rule ◽  
Quark Spin ◽  
Quark Flavor ◽  
Quark Orbital Angular Momentum ◽  
Quark Flavors ◽  
Partition Factor

Analytical and numerical results, for the orbital and spin content carried by different quark flavors in the baryons, are given in the chiral quark model with symmetry breaking. The reduction of the quark spin, due to the spin dilution in the chiral splitting processes, is transferred into the orbital motion of quarks and antiquarks. The orbital angular momentum for each quark flavor in the proton as a function of the partition factor κ and the chiral splitting probability a is shown. The cancellation between the spin and orbital contributions in the spin sum rule and in the baryon magnetic moments is discussed.

scholarly journals SPIN AND ORBITAL ANGULAR MOMENTUM IN THE PROTON

2009 ◽  
Vol 18 (05n06) ◽  
pp. 1116-1134 ◽  
Author(s):  
ANTHONY W. THOMAS
Keyword(s):  
Angular Momentum ◽  
Orbital Angular Momentum ◽  
Current Data ◽  
Proton Spin ◽  
Current Status ◽  
Nucleon Structure ◽  
Upper Limits ◽  
European Muon Collaboration ◽  
Spin Crisis

Since the announcement of the proton spin crisis by the European Muon Collaboration there has been considerable progress in unravelling the distribution of spin and orbital angular momentum within the proton. We review the current status of the problem, showing that not only have strong upper limits have been placed on the amount of polarized glue in the proton but that the experimental determination of the spin content has become much more precise. It is now clear that the origin of the discrepancy between experiment and the naive expectation of the fraction of spin carried by the quarks and anti-quarks in the proton lies in the non-perturbative structure of the proton. We explain how the features expected in a modern, relativistic and chirally symmetric description of nucleon structure naturally explain the current data. The consequences of this explanation for the presence of orbital angular momentum on quarks and gluons is reviewed and comparison made with recent results from lattice QCD and experimental data.

scholarly journals Quark Spin-Orbit Correlations

2015 ◽  
Vol 37 ◽  
pp. 1560036 ◽  
Author(s):  
Cédric Lorcé
Keyword(s):  
Angular Momentum ◽  
Phase Space ◽  
Orbital Angular Momentum ◽  
Valence Quark ◽  
Complete Characterization ◽  
Proton Spin ◽  
Spin Orbit ◽  
Parton Distributions ◽  
Transverse Momentum Dependent ◽  
Quark Spin

The proton spin puzzle issue focused the attention on the parton spin and orbital angular momentum contributions to the proton spin. However, a complete characterization of the proton spin structure requires also the knowledge of the parton spin-orbit correlation. We showed that this quantity can be expressed in terms of moments of measurable parton distributions. Using the available phenomenological information about the valence quarks, we concluded that this correlation is negative, meaning that the valence quark spin and kinetic orbital angular momentum are, in average, opposite. The quark spin-orbit correlation can also be expressed more intuitively in terms of relativistic phase-space distributions, which can be seen as the mother distributions of the standard generalized and transverse-momentum dependent parton distributions. We present here for the first time some examples of the general multipole decomposition of these phase-space distributions.

QUARK ORBITAL ANGULAR MOMENTUM AND GENERALIZED PARTON DISTRIBUTIONS

2003 ◽  
Vol 18 (08) ◽  
pp. 1303-1309 ◽  
Author(s):  
XIANGDONG JI
Keyword(s):  
Angular Momentum ◽  
Quantum Chromodynamics ◽  
Orbital Angular Momentum ◽  
Parton Distributions ◽  
Generalized Parton Distributions ◽  
Quark Orbital Angular Momentum

In this talk, I review the merit of introducing and measuring the quark orbital angular momentum contribution to the spin of the nucleon in the context of quantum chromodynamics.

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