Improved analysis of isovector nucleon matrix elements with N f = 2 + 1 flavors of O ( a ) improved Wilson fermions

• Published in: Physical review. D 2024-04, Vol.109 (7), Article 074507
• Main Authors: Djukanovic, Dalibor, von Hippel, Georg, Meyer, Harvey B., Ottnad, Konstantin, Wittig, Hartmut
• Format: Article
• Language: English
• ISSN: 2470-0010; 2470-0029
• DOI: 10.1103/PhysRevD.109.074507

We present an update of our determination of the isovector charges g A u − d , g S u − d and g T u − d , and the isovector twist-2 forward matrix elements ⟨ x ⟩ u − d , ⟨ x ⟩ Δ u − Δ d and ⟨ x ⟩ δ u − δ d on the N f = 2 + 1 gauge ensembles generated by the Coordinated Lattice Simulations (CLS) effort. We have significantly extended our coverage of the parameter space by adding ensembles at the physical pion mass and fine lattice spacing, at nearly physical pion masses and very fine lattice spacings, and at very large physical lattice volumes, enabling a well-controlled extrapolation to the physical point. Another major improvement is achieved owing to the extended range of source-sink separations, which allows us to perform two-state fits to summed correlator ratios, leading to a much higher level of control over excited-state effects. Systematic uncertainties from the chiral, continuum and infinite-volume extrapolations are incorporated via model averages based on the Akaike information criterion. Our final results at the physical point are g A u − d = 1.254 ( 19 ) stat ( 15 ) sys [ 24 ] total , g S u − d = 1.203 ( 77 ) stat ( 81 ) sys [ 112 ] total , g T u − d = 0.993 ( 15 ) stat ( 05 ) sys [ 16 ] total , ⟨ x ⟩ u − d = 0.153 ( 15 ) stat ( 10 ) sys [ 17 ] total , ⟨ x ⟩ Δ u − Δ d = 0.207 ( 15 ) stat ( 06 ) sys [ 16 ] total , and ⟨ x ⟩ δ u − δ d = 0.195 ( 17 ) stat ( 15 ) sys [ 23 ] total . While our results for the isovector charges are in excellent agreement with the FLAG 21 averages, we note that our error for the tensor charge g T u − d is considerably smaller.