2019/11/30 by Gunnar S. Bali, Lorenzo Barca, Sara Collins +7
Physics and Astronomy · #Ansatz #Effective field theory #High-Energy Particle Collisions Research #Isovector #Lattice QCD #Lattice field theory #Nuclear physics research studies #Nucleon #Observable #Pion #Pseudoscalar #Pseudoscalar meson #Quantum Chromodynamics and Particle Interactions #hep-lat #hep-ph
paper · pdf · doi:10.1007/jhep05(2020)126
published as JHEP05 (2020) 126
openalex created_date 2019/12/05 · openalex publication_date 2020/05/26 · arxiv created 2020/05/29 · arxiv updated 2020/06/01 · openalex updated_date 2026/08/05
A bstract We present a new analysis method that allows one to understand and model excited state contributions in observables that are dominated by a pion pole. We apply this method to extract axial and (induced) pseudoscalar nucleon isovector form factors, which satisfy the constraints due to the partial conservation of the axial current up to expected discretization effects. Effective field theory predicts that the leading contribution to the (induced) pseudoscalar form factor originates from an exchange of a virtual pion, and thus exhibits pion pole dominance. Using our new method, we can recover this behavior directly from lattice data. The numerical analysis is based on a large set of ensembles generated by the CLS effort, including physical pion masses, large volumes (with up to 96 3 × 192 sites and Lm π = 6 . 4), and lattice spacings down to 0.039 fm, which allows us to take all the relevant limits. We find that some observables are much more sensitive to the choice of parametrization of the form factors than others. On the one hand, the z -expansion leads to significantly smaller values for the axial dipole mass than the dipole ansatz ( MAz-exp <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mi>A</mml:mi> <mml:mrow> <mml:mi>z</mml:mi> <mml:mo>−</mml:mo> <mml:mo>exp</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> = 1 . 02(10) GeV versus MAdipole <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>M</mml:mi> <mml:mi>A</mml:mi> <mml:mtext>dipole</mml:mtext> </mml:msubsup> </mml:math> = 1 . 31(8) GeV). On the other hand, we find that the result for the induced pseudoscalar coupling at the muon capture point is almost independent of the choice of parametrization ( gP∗ z-exp <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>g</mml:mi> <mml:mi>P</mml:mi> <mml:mrow> <mml:mo>∗</mml:mo> <mml:mi>z</mml:mi> <mml:mo>−</mml:mo> <mml:mo>exp</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> = 8 . 68(45) and gP∗ dipole <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msubsup> <mml:mi>g</mml:mi> <mml:mi>P</mml:mi> <mml:mrow> <mml:mo>∗</mml:mo> <mml:mtext>dipole</mml:mtext> </mml:mrow> </mml:msubsup> </mml:math> = 8 . 30(24)), and is in good agreement with both, chiral perturbation theory predictions and experimental measurement via ordinary muon capture. We also determine the axial coupling constant g A .