Quark and glue momenta and angular momenta in the proton — A lattice calculation

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We report a complete calculation of the quark and glue momenta and angular momenta in the proton. These include the quark contributions from both the connected and disconnected insertions. The calculation is carried out on a 163 ×24 quenched lattice at β = 6.0 and for Wilson fermions with κ = 0.154,0.155, and 0.1555 which correspond to pion masses at 650, 538, and 478 MeV. The quark loops are calculated with Z4 noise and signal-to-noise is improved further with unbiased subtractions. The glue operator is comprised of gauge-field tensors constructed from the overlap operator. The u and d quark momentum/angular momentum fraction is 0.66(5)/0.72(5), the strange momentum/angular momentum fraction is 0.024(6)/0.023(7), and that of the glue is 0.31(6)/0.25(8). The orbital angular momenta of the quarks are obtained from subtracting the quark spins from the corresponding angular momentum components. As a result, the quark orbital angular momentum constitutes 0.50(2) of the proton spin, with almost all of it coming from the disconnected insertion. The quark spin carries a fraction 0.25(12) and glue carries a fraction 0.25(8) of the total proton spin.

Original languageEnglish
JournalProceedings of Science
StatePublished - 2011
Event29th International Symposium on Lattice Field Theory, Lattice 2011 - Squaw Valley, Lake Tahoe, United States
Duration: Jul 10 2011Jul 16 2011

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