Quark flavor decomposition of the nucleon axial form factors

C Alexandrou,G Koutsou,K Hadjiyiannakou,S Bacchio,M Constantinou,K Jansen

doi:10.1103/physrevd.104.074503

Abstract

We present results on the isoscalar form factors including the disconnected contributions, as well as on the strange and charm quark form factors. Using previous results on the isovector form factors, we determine the flavor decomposition of the nucleon axial form factors. These are computed using an ensemble of $N_f=2+1+1$ twisted mass fermions simulated with physical values of quark masses. We investigate the SU(3) flavor symmetry and show that there is up to 10\% breaking for the axial and up to 50\% for the induced pseudoscalar form factors. By fitting the $Q^2$-dependence, we determined the corresponding root mean square radii. The pseudoscalar coupling of the $\eta$ meson and the nucleon is found to be $g_{\eta NN}=3.7(1.0)(0.7)$, and the Goldberger-Treiman discrepancy for the octet combination about 50\%.

Highlights

Axial form factors play a key role in the interactions of nucleons with the W and Z bosons, the carriers of the weak force
We investigate the SU(3) flavor symmetry and show that there is up to 10% breaking for the axial and up to 50% for the induced pseudoscalar form factors
We find that there is up to 10% breaking for the axial and up to 50% for the induced pseudoscalar form factors

Summary

Introduction

Axial form factors play a key role in the interactions of nucleons with the W and Z bosons, the carriers of the weak force. They provide insights into the structure of the nucleon that in turn can affect our ability to compute cross sections that may aid us into revealing new physics. Neutrino elastic scattering on protons is sensitive to the strange axial form factor of the proton GsAðQ2Þ, which for Q2 1⁄4 0 determines the strange quark contribution to the proton spin Δs. The role of strange quarks is important for calculating the cross sections for a class of popular cold dark matter candidates [1]. A first measurement of parity-violating asymmetries in forward elastic electron-proton scattering by HAPPEx [2] combined with data from neutrino and antineutrino-proton elastic scattering cross sections from Brookhaven E734 [3] determined

Methods

Results

Conclusion