Nucleon axial and pseudoscalar form factors from lattice QCD at the physical point

C Alexandrou,C Urbach,J Finkenrath,K Hadjiyiannakou,T Leontiou,P Dimopoulos,K Jansen,B Kostrzewa,M Constantinou,Extended Twisted Mass Collaboration ,S Bacchio,G Koutsou

doi:10.1103/physrevd.103.034509

Abstract

We compute the nucleon axial and induced pseudoscalar form factors using three ensembles of gauge configurations, generated with dynamical light quarks with mass tuned to approximately their physical value. One of the ensembles also includes the strange and charm quarks with their mass close to physical. The latter ensemble has large statistics and finer lattice spacing and it is used to obtain final results, while the other two are used for assessing volume effects. The pseudoscalar form factor is also computed using these ensembles. We examine the momentum dependence of these form factors as well as relations based on pion pole dominance and the partially conserved axial-vector current hypothesis.

Highlights

A central aim of on-going experimental and theoretical studies is the understanding of the structure of the proton and the neutron arising from the complex nature of the strong interactions
We summarize below the setup used by other groups to compute the isovector axial and pseudoscalar form factors: (i) The PNDME Collaboration [46] used a hybrid action with Nf 1⁄4 2 þ 1 þ 1 HISQ configurations generated by the MILC Collaboration with lattice spacing a ≃ 0.0871 fm, lattice volume 643 × 128 and mπ 1⁄4 130 MeV in the sea and clover improved valence quarks with mπ 1⁄4 138 MeV
The ensembles were generated using a tree-level Symanzik-improved gauge action and Nf 1⁄4 2 þ 1 clover-improved fermions. Their axialvector current is OðaÞ-improved using nonperturbatively determined coefficients. We show their results from the physical point ensemble with the finer lattice spacing of a 1⁄4 0.064 fm, volume 963 × 192 and mπ 1⁄4 130 MeV, referred to as E250 in Ref. [49]

Summary

Introduction

A central aim of on-going experimental and theoretical studies is the understanding of the structure of the proton and the neutron arising from the complex nature of the strong interactions. The electron scattering off protons is a well developed experimental approach used in such studies. An outcome of the multiyears experimental programs in major facilities has been the precise measurement of the electromagnetic form factors, see e.g., Refs.

Methods

Results

Conclusion