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Nucleon Spin and Momentum Decomposition Using Lattice QCD Simulations.
C Alexandrou1,2, M Constantinou3, K Hadjiyiannakou2
1Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus.
Physical Review Letters
|October 21, 2017
Summary
Lattice quantum chromodynamics calculations reveal the nucleon spin contributions from quarks and gluons. Quarks carry 0.408 of the nucleon
Area of Science:
- Nuclear Physics
- Particle Physics
- Quantum Chromodynamics
Background:
- The nucleon spin crisis highlights discrepancies in understanding the proton's spin.
- Valence and sea quarks, along with gluons, are fundamental constituents of the nucleon.
Purpose of the Study:
- To precisely determine the spin contributions of quarks and gluons within the nucleon.
- To investigate the quark intrinsic spin contribution to the nucleon's total angular momentum.
Main Methods:
- Utilizing lattice quantum chromodynamics (LQCD) simulations.
- Employing gauge configurations with dynamical light quarks at physical pion mass.
- Calculating spin and momentum fractions in the modified minimal subtraction scheme at 2 GeV.
Main Results:
- The total angular momentum carried by quarks (u+d+s) is J_{u+d+s}=0.408(61)_{stat}(48)_{syst}.
- The gluon contribution to nucleon spin is J_{g}=0.133(11)_{stat}(14)_{syst}.
- The quark intrinsic spin contribution is 1/2ΔΣ_{u+d+s}=0.201(17)_{stat}(5)_{syst}.
Conclusions:
- The combined quark and gluon contributions (J_{N}=0.54(6)_{stat}(5)_{syst}) are consistent with the nucleon spin sum rule.
- Computed quark and gluon momentum fractions sum to 1.07(12)_{stat}(10)_{syst}, satisfying the momentum sum rule.
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