Nucleon charges and form factors using clover and HISQ ensembles

Abstract

We present high statistics ($\mathcal{O}(2\times 10^5)$ measurements) preliminary results on (i) the isovector charges, $g_{A,S,T}^{u-d}$, and form factors, $G_E^{u-d}(Q^2)$, $G_M^{u-d}(Q^2)$, $G_A^{u-d}(Q^2)$, ${\tilde{G}}_P^{u-d}(Q^2)$, $G_P^{u-d}(Q^2)$, on six 2+1-flavor Wilson-clover ensembles generated by the JLab/W&M/LANL/MIT collaboration with lattice parameters given in Table 1. Examples of the impact of using different estimates of the excited state spectra are given for the clover-on-clover data, and as discussed in [1], the biggest difference on including the lower energy (close to $N\pi$ and $N\pi \pi$) states is in the axial channel. (ii) Flavor diagonal axial, tensor and scalar charges, $g_{A,S,T}^{u,d,s}$, are calculated with the clover-on-HISQ formulation using nine 2+1+1-flavor HISQ ensembles generated by the MILC collaboration [2] with lattice parameters given in Table 2. Once finished, the calculations of $g_{A,T}^{u,d,s}$ will update the results given in Refs.[3,4]. The estimates for $g_S^{u,d,s}$ and ${\sigma }_{N\pi }$ are new. Overall, a large part of the focus is on understanding the excited state contamination (ESC), and the results discussed provide a partial status report on developing defensible analyses strategies that include contributions of possible low-lying excited states to individual nucleon matrix elements.

Comments: 7 pages, 7 figures, 37th International Symposium on Lattice Field Theory - Lattice 2019, 16-22 June 2019, Wuhan, China