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Title: Axial-vector form factors of the nucleon from lattice QCD

Abstract

In this paper, we present results for the form factors of the isovector axial vector current in the nucleon state using large scale simulations of lattice QCD. The calculations were done using eight ensembles of gauge configurations generated by the MILC collaboration using the HISQ action with 2 + 1 + 1 dynamical flavors. These ensembles span three lattice spacings a ≈ 0.06 , 0.09, and 0.12 fm and light-quark masses corresponding to the pion masses M π ≈ 135, 225, and 310 MeV. High-statistics estimates allow us to quantify systematic uncertainties in the extraction of G A (Q 2) and the induced pseudoscalar form factor G P(Q 2) . We perform a simultaneous extrapolation in the lattice spacing, lattice volume and light-quark masses of the axial charge radius r A data to obtain physical estimates. Using the dipole ansatz to fit the Q 2 behavior we obtain r A | dipole = 0.49(3) fm , which corresponds to M A = 1.39(9) GeV , and is consistent with M A = 1.35(17) GeV obtained by the miniBooNE collaboration. The estimate obtained using the z -expansion is r A | z - expansion = 0.46(6) fm, and the combined resultmore » is r A | combined = 0.48(4) fm. Analysis of the induced pseudoscalar form factor G P (Q 2) yields low estimates for g* P and g πNN compared to their phenomenological values. To understand these, we analyze the partially conserved axial current (PCAC) relation by also calculating the pseudoscalar form factor. Lastly, we find that these low values are due to large deviations in the PCAC relation between the three form factors, and in the pion-pole dominance hypothesis.« less

Authors:
ORCiD logo [1];  [1];  [2]; ORCiD logo [1]; ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Michigan State Univ., East Lansing, MI (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE Office of Science (SC), High Energy Physics (HEP) (SC-25); USDOE Laboratory Directed Research and Development (LDRD) Program
OSTI Identifier:
1415378
Report Number(s):
LA-UR-17-23678
Journal ID: ISSN 2470-0010; PRVDAQ
Grant/Contract Number:
AC52-06NA25396; AC02-05CH11231; KA-1401020
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Physical Review D
Additional Journal Information:
Journal Volume: 96; Journal Issue: 11; Journal ID: ISSN 2470-0010
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; Axial form factors; nucleons; lattice QCD

Citation Formats

Gupta, Rajan, Jang, Yong-Chull, Lin, Huey-Wen, Yoon, Boram, and Bhattacharya, Tanmoy. Axial-vector form factors of the nucleon from lattice QCD. United States: N. p., 2017. Web. doi:10.1103/PhysRevD.96.114503.
Gupta, Rajan, Jang, Yong-Chull, Lin, Huey-Wen, Yoon, Boram, & Bhattacharya, Tanmoy. Axial-vector form factors of the nucleon from lattice QCD. United States. doi:10.1103/PhysRevD.96.114503.
Gupta, Rajan, Jang, Yong-Chull, Lin, Huey-Wen, Yoon, Boram, and Bhattacharya, Tanmoy. 2017. "Axial-vector form factors of the nucleon from lattice QCD". United States. doi:10.1103/PhysRevD.96.114503.
@article{osti_1415378,
title = {Axial-vector form factors of the nucleon from lattice QCD},
author = {Gupta, Rajan and Jang, Yong-Chull and Lin, Huey-Wen and Yoon, Boram and Bhattacharya, Tanmoy},
abstractNote = {In this paper, we present results for the form factors of the isovector axial vector current in the nucleon state using large scale simulations of lattice QCD. The calculations were done using eight ensembles of gauge configurations generated by the MILC collaboration using the HISQ action with 2 + 1 + 1 dynamical flavors. These ensembles span three lattice spacings a ≈ 0.06 , 0.09, and 0.12 fm and light-quark masses corresponding to the pion masses Mπ ≈ 135, 225, and 310 MeV. High-statistics estimates allow us to quantify systematic uncertainties in the extraction of GA (Q2) and the induced pseudoscalar form factor GP(Q2) . We perform a simultaneous extrapolation in the lattice spacing, lattice volume and light-quark masses of the axial charge radius rA data to obtain physical estimates. Using the dipole ansatz to fit the Q2 behavior we obtain rA |dipole = 0.49(3) fm , which corresponds to MA = 1.39(9) GeV , and is consistent with MA = 1.35(17) GeV obtained by the miniBooNE collaboration. The estimate obtained using the z -expansion is rA |z - expansion = 0.46(6) fm, and the combined result is rA | combined = 0.48(4) fm. Analysis of the induced pseudoscalar form factor GP (Q2) yields low estimates for g*P and gπNN compared to their phenomenological values. To understand these, we analyze the partially conserved axial current (PCAC) relation by also calculating the pseudoscalar form factor. Lastly, we find that these low values are due to large deviations in the PCAC relation between the three form factors, and in the pion-pole dominance hypothesis.},
doi = {10.1103/PhysRevD.96.114503},
journal = {Physical Review D},
number = 11,
volume = 96,
place = {United States},
year = 2017,
month =
}

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  • We evaluate the nucleon axial form factor, G{sub A}(q{sup 2}), and induced pseudoscalar form factor, G{sub p}(q{sup 2}), as well as the pion-nucleon form factor, G{sub {pi}}{sub NN}(q{sup 2}), in lattice QCD. We also evaluate the corresponding nucleon to {delta} transition form factors, C{sub 5}{sup A}(q{sup 2}) and C{sub 6}{sup A}(q{sup 2}), and the pion-nucleon-{delta} form factor G{sub {pi}}{sub N{delta}}(q{sup 2}). The nucleon form factors are evaluated in the quenched theory and with two degenerate flavors of dynamical Wilson fermions. The nucleon to {delta} form factors, besides Wilson fermions, are evaluated using domain wall valence fermions with staggered sea quarkmore » configurations for pion masses as low as about 350 MeV. Using these form factors, together with an evaluation of the renormalized quark mass, we investigate the validity of the diagonal and nondiagonal Goldberger-Treiman relations. The ratios G{sub {pi}}{sub N{delta}}(q{sup 2})/G{sub {pi}}{sub NN}(q{sup 2}) and 2C{sub 5}{sup A}(q{sup 2})/G{sub A}(q{sup 2}) are constant as a function of the momentum transfer squared and show almost no dependence on the quark mass. We confirm equality of these two ratios consistent with the Goldberger-Treiman relations extracting a mean value of 1.61(2)« less
  • No abstract prepared.
  • The strange quark contribution to the vector and axial form factors of the nucleon has been determined for momentum transfers in the range 0.45<Q{sup 2}<1.0 GeV{sup 2}. The results are obtained via a combined analysis of forward-scattering, parity-violating elastic e-vectorp asymmetry data from the G0 and HAPPEx experiments at Jefferson Lab and elastic {nu}p- and {nu}p-scattering data from Experiment 734 at Brookhaven National Laboratory. The parity-violating asymmetries measured in elastic e-vectorp scattering at forward angles establish a relationship between the strange vector form factors G{sub E}{sup s} and G{sub M}{sup s}, with little sensitivity to the strange axial form factormore » G{sub A}{sup s}. However, elastic neutrino scattering at low Q{sup 2} is dominated by the axial form factor, with some significant sensitivity to the vector form factors as well. Combination of the two data sets allows the simultaneous extraction of G{sub E}{sup s},G{sub M}{sup s}, and G{sub A}{sup s} over a significant range of Q{sup 2} for the very first time. The Q{sup 2} dependence of the strange axial form factor suggests that the strange quark contribution to the proton spin, {delta}s, is negative.« less
  • We present results on the nucleon axial form factors within lattice QCD using two flavors of degenerate twisted mass fermions. Volume effects are examined using simulations at two volumes of spatial length L=2.1 fm and L=2.8 fm. Cut-off effects are investigated using three different values of the lattice spacings, namely a=0.089 fm, a=0.070 fm and a=0.056 fm. The nucleon axial charge is obtained in the continuum limit and chirally extrapolated to the physical pion mass enabling comparison with experiment.