Nucleon form factors on a large volume lattice near the physical point in 2+1 flavor QCD

Ken-Ichi Ishikawa,Akira Ukawa,Yoshinobu Kuramashi,Shoichi Sasaki,Takeshi Yamazaki,Natsuki Tsukamoto

doi:10.1103/physrevd.98.074510

Abstract

We present results for the isovector nucleon form factors measured on a $96^4$ lattice at almost the physical pion mass with a lattice spacing of 0.085 fm in 2+1 flavor QCD. The configurations are generated with the stout-smeared $O(a)$-improved Wilson quark action and the Iwasaki gauge action at $\beta$=1.82. The pion mass at the simulation point is about 146 MeV. A large spatial volume of $(8.1~{\rm fm})^3$ allows us to investigate the form factors in the small momentum transfer region. We determine the isovector electric radius and magnetic moment from nucleon electric ($G_E$) and magnetic ($G_M$) form factors as well as the axial-vector coupling $g_A$. We also report on the results of the axial-vector ($F_A$), induced pseudoscalar ($F_P$) and pseudoscalar ($G_P$) form factors in order to verify the axial Ward-Takahashi identity in terms of the nucleon matrix elements, which may be called the generalized Goldberger-Treiman relation.

Highlights

The nucleon vector and axial elastic form factors are good probes to investigate the internal structure of the nucleon [1]
We present results for the isovector nucleon form factors measured on a 964 lattice at almost the physical pion mass with a lattice spacing of 0.085 fm in 2 þ 1 flavor QCD
We have studied the nucleon form factors calculated in 2 þ 1-flavor QCD near the physical point in a large spatial volume ð8.1 fmÞ3 at a single lattice spacing of 0.085 fm

Summary

Introduction

The nucleon vector and axial elastic form factors are good probes to investigate the internal structure of the nucleon [1]. Great theoretical and experimental efforts have been devoted to improving our knowledge of the nucleon structure, there are several unsolved problems associated with fundamental properties of the proton and neutron. The neutron lifetime puzzle, where the discrepancy between the results of beam experiments and storage experiments remains unsolved, is another open question that deserves further investigation in terms of the nucleon axial-vector coupling gA [6]

Objectives

Results

Conclusion