g_A from Lattice QCD

Rajan Gupta
2019 Zenodo  
Following a short overview of the lattice QCD calculations of isovector charges of the nucleon, I will present results for isovector g_A=1.218(25)(30) obtained by the PNDME collaboration using eleven 2+1+1-flavor HISQ ensembles generated by the MILC collaboration. The talk will cover details of the control over excited state contamination and the the chiral-continuum-finite volume fits leading to the final results. A careful comparison will be made with recent CalLat result g_A=1.271(13). We
more » ... _A=1.271(13). We show that the difference comes from the chiral and continuum extrapolation: CalLat data on the two physical mass ensembles have large errors and do not contribute significantly to the fits, i.e., their estimate is essentially based on fits to data with Mπ ≥ 220 MeV, and they have not simulated the fine a = 0.57 fm ensembles that pull down our estimate. Our conclusion is that more work is needed to understand and resolve the systematics at the percent level.
doi:10.5281/zenodo.2565460 fatcat:zay4vupanje3jlpfmjoxdroyhe