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14-18 May 2018
Jefferson Lab - CEBAF Center
US/Eastern timezone

Controlling excited-state contributions to nucleon charges g_A, g_T and g_S in lattice QCD calculations

17 May 2018, 15:00
20m
Auditorium (Jefferson Lab - CEBAF Center)

Auditorium

Jefferson Lab - CEBAF Center

Speaker

Mr Colin Egerer (William and Mary)

Description

The axial charge of the nucleon remains a quantity of phenomenological importance as it relates to nuclear beta decay and the degree of chiral symmetry breaking in QCD. Defined simply as the axial vector form factor at zero momentum transfer, the axial charge of the nucleon has long been a benchmark calculation in Lattice Field Theory. The bulk of Lattice determinations of the nucleon axial charge have, however, historically differed from the world average by roughly 10%. This systematic discrepancy is today mainly attributed to excited-state contamination. The variational method and the Jacobi smearing technique have seen extensive use in lattice calculations in the hopes of taming excited-state contributions to nuclear properties. By employing a basis of several interpolators, including some of hybrid character, and utilizing the quark smearing algorithm Distillation, we demonstrate an earlier onset of a plateau region in extracted nucleon matrix elements with reduced statistical uncertainties, when compared to analyses using just the variational method or single smeared interpolators. This presentation will highlight our methodology and results for the isovector axial charge of the nucleon on two isoclover lattice ensembles, in good agreement with experiment. Having demonstrated an effective reduction in excited-state effects, we extend our presentation to include precision determinations of the isovector scalar and tensor charges of the nucleon. If constrained precisely, these results will provide useful theoretical input to the ongoing experimental search for BSM physics.

Primary author

Mr Colin Egerer (William and Mary)

Co-authors

Dr David Richards (Jefferson Lab) Dr Frank Winter (JLab)

Presentation Materials