An accurate calculation of the nucleon axial charge with lattice QCD

Evan Berkowitz, David Brantley, Chris Bouchard, Chia Cheng Chang, M. A. Clark, Nicholas Garron, Balint Joo, Thorsten Kurth, Chris Monahan, Henry Monge-Camacho, Amy Nicholson, Kostas Orginos, Enrico Rinaldi, Pavlos Vranas, Andre Walker-Loud

Apr 2017

Abstract

We report on a lattice QCD calculation of the nucleon axial charge, $g_{A}$ , using M $" o b i u s D o m a i n - W a l l f e r m i o n s s o l v e d o n t h e d y n a m i c a l $ N_{f} = 2 + 1 + 1 $ H I S Q e n s e m b l e s a f t e r t h e y a r e s m e a r e d u s i n g t h e g r a d i e n t - f l o w a l g o r i t h m . T h e c a l c u l a t i o n i s p e r f o r m e d w i t h t h r e e p i o n m a s s e s, $ m_{π} \sim \3 10, 220, 130 $ M e V . T h r e e l a t t i c e s p a c i n g s ($ a \sim \0 .15, 0.12, 0.09 $ f m) a r e u s e d w i t h t h e h e a v i e s t p i o n m a s s, w h i l e t h e c o a r s e s t t w o s p a c i n g s a r e u s e d o n t h e m i d d l e p i o n m a s s a n d o n l y t h e c o a r s e s t s p a c i n g i s u s e d w i t h t h e n e a r p h y s i c a l p i o n m a s s . O n t h e $ m_{π} \sim 220 $ M e V, $ a \sim 0.12 $ f m p o i n t, a d e d i c a t e d v o l u m e s t u d y i s p e r f o r m e d w i t h $ m_{π} L \sim \3 .22, 4.29, 5.36 $ . U s i n g a n e w s t r a t e g y m o t i v a t e d b y t h e F e y n m a n - H e l l m a n n T h e o r e m, w e a c h i e v e a p r e c i s e d e t e r m i n a t i o n o f $ g_{A} $ w i t h r e l a t i v e l y l o w s t a t i s t i c s, a n d d e m o n s t r a b l e c o n t r o l o v e r t h e e x c i t e d s t a t e, c o n t i n u u m, i n f i n i t e v o l u m e a n d c h i r a l e x t r a p o l a t i o n s y s t e m a t i c u n c e r t a i n t i e s, t h e l a t t e r o f w h i c h r e m a i n s t h e d o m i n a n t u n c e r t a i n t y . O u r f i n a l d e t e r m i n a t i o n a t 2.6$ % total uncertainty is $g_{A} = 1.278 (21) (26)$ , with the first uncertainty including statistical and systematic uncertainties from fitting and the second including model selection systematics related to the chiral and continuum extrapolation. The largest reduction of the second uncertainty will come from a greater number of pion mass points as well as more precise lattice QCD results near the physical pion mass.

Type

Journal article

An accurate calculation of the nucleon axial charge with lattice QCD

Abstract

Enrico Rinaldi

Research Scientist