2018/06/30 by Huey-Wen Lin, Rajan Gupta, Boram Yoon +2
Chemistry · Physics and Astronomy · #Chemistry #Crystallography #High-Energy Particle Collisions Research #Lattice (music) #Lattice QCD #Particle physics #Particle physics theoretical and experimental studies #Physics #Pion #Quantum Chromodynamics and Particle Interactions #Quark #hep-lat #hep-ph
paper · pdf · doi:10.1103/physrevd.98.094512
published as Phys. Rev. D 98, 094512 (2018) · Published version. 8 pages 4 figures
openalex created_date 2018/07/10 · openalex publication_date 2018/11/30 · arxiv created 2018/12/03 · arxiv updated 2018/12/05 · openalex updated_date 2026/08/06
We present the first chiral-continuum extrapolated up, down, and strange quark spin contribution to the proton spin using lattice QCD. For the connected contributions, we use 11 ensembles of 2+1+1-flavor of highly improved staggered quarks (HISQ) generated by the MILC Collaboration. They cover four lattice spacings, a\ensuremath≈0.15,0.12,0.09,0.06 fm, and three pion masses, M_\ensuremathπ\ensuremath≈315,220,135 MeV, of which two are at the physical pion mass. The disconnected strange calculations are done on seven of these ensembles, covering the four lattice spacings but only one with the physical pion mass. The disconnected light quark calculation was done on six ensembles at two values of M_\ensuremathπ\ensuremath≈315,220 MeV. High-statistics estimates on each ensemble for all three quantities allow us to quantify systematic uncertainties and perform a simultaneous chiral-continuum extrapolation in the lattice spacing and the light-quark mass. Our final results are \mathrm\ensuremathΔu\ensuremath≡⟨1⟩_\mathrm\ensuremathΔu+=0.777(25)(30), \mathrm\ensuremathΔd\ensuremath≡⟨1⟩_\mathrm\ensuremathΔd+=\ensuremath-0.438(18)(30), and \mathrm\ensuremathΔs\ensuremath≡⟨1⟩_\mathrm\ensuremathΔs+=\ensuremath-0.053(8), adding up to a total quark contribution to proton spin of \ensuremath∑q=u,d,s((1)/(2)\mathrm\ensuremathΔq)=0.143(31)(36). The second error is the systematic uncertainty associated with the chiral-continuum extrapolation. These results are obtained without model assumptions and are in good agreement with the recent COMPASS analysis 0.13<(1)/(2)\mathrm\ensuremathΔ\mathrm\ensuremathΣ<0.18 and with the \mathrm\ensuremathΔq obtained from various global analyses of polarized beam or target data.