Nucleon axial form factors from two-flavour Lattice QCD

TL;DR

This study investigates the nucleon axial and pseudoscalar form factors using two-flavour lattice QCD, highlighting the importance of accounting for excited-state contributions to obtain accurate results.

Contribution

It provides a systematic analysis of excited-state effects on form factors and demonstrates the effectiveness of summed operator insertions over naive plateau fits.

Findings

Excited-state contributions significantly affect form factor measurements.

Naive plateau fits underestimate excited-state effects.

Summed operator insertions correctly account for these contributions.

Abstract

We present preliminary results on the axial form factor $G_A(Q^2)$ and the induced pseudoscalar form factor $G_P(Q^2)$ of the nucleon. A systematic analysis of the excited-state contributions to form factors is performed on the CLS ensemble `N6' with $m_\pi = 340 \ \text{MeV}$ and lattice spacing $a \sim 0.05 \ \text{fm}$. The relevant three-point functions were computed with source-sink separations ranging from $t_s \sim 0.6 \ \text{fm}$ to $t_s \sim \ 1.4 \ \text{fm}$. We observe that the form factors suffer from non-trivial excited-state contributions at the source-sink separations available to us. It is noted that naive plateau fits underestimate the excited-state contributions and that the method of summed operator insertions correctly accounts for these effects.