Nucleon isovector charges and twist-2 matrix elements with Nf=2+1 dynamical Wilson quarks

We present results from a lattice QCD study of nucleon matrix elements at vanishing momentum transfer for local and twist-2 isovector operator insertions. Computations are performed on gauge ensembles with nonperturbatively improved Nf=2+1 Wilson fermions, covering four values of the lattice spacing...

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Bibliographic Details
Published in:Physical review. D 2019-08, Vol.100 (3), p.1
Main Authors: Harris, Tim, von Hippel, Georg, Junnarkar, Parikshit, Meyer, Harvey B, Ottnad, Konstantin, Wilhelm, Jonas, Wittig, Hartmut, Wrang, Linus
Format: Article
Language:English
Subjects:
Energy gap
Extrapolation
Fermions
Helicity
Momentum transfer
Nucleons
Pions
Quadratures
Quantum chromodynamics
Quarks
Systematic errors
Tensors
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Summary:We present results from a lattice QCD study of nucleon matrix elements at vanishing momentum transfer for local and twist-2 isovector operator insertions. Computations are performed on gauge ensembles with nonperturbatively improved Nf=2+1 Wilson fermions, covering four values of the lattice spacing and pion masses down to Mπ≈200  MeV. Several source-sink separations (typically ∼1.0 to ∼1.5  fm) allow us to assess excited-state contamination. Results on individual ensembles are obtained from simultaneous two-state fits across all observables and all available source-sink separations with the energy gap as a common fit parameter. Renormalization has been performed nonperturbatively using the Rome-Southampton method for all but the finest lattice spacing for which an extrapolation has been used. Physical results are quoted in the MS¯ scheme at a scale of μ=2  GeV and are obtained from a combined chiral, continuum, and finite-size extrapolation. For the nucleon isovector axial, scalar, and tensor charges we find physical values of gAu−d=1.242(25)stat(+00−31)sys, gSu−d=1.13(11)stat(+07−06)sys and gTu−d=0.965(38)stat(+13−41)sys, respectively, where individual systematic errors in each direction from the chiral, continuum, and finite-size extrapolation have been added in quadrature. Our final results for the isovector average quark momentum fraction and the isovector helicity and transversity moments are given by ⟨x⟩u−d=0.180(25)stat(+14−06)sys, ⟨x⟩Δu−Δd=0.221(25)stat(+10−00)sys, and ⟨x⟩δu−δd=0.212(32)stat(+20−10)sys, respectively.
ISSN:2470-0010
2470-0029
DOI:10.1103/PhysRevD.100.034513