Excited state contamination in nucleon structure calculations

TL;DR

This paper investigates excited state contamination in nucleon structure calculations by varying operator insertion times and source-sink separations, using lattice QCD simulations with improved fermions and low pion masses.

Contribution

It introduces a systematic method to quantify and subtract excited state contamination using a two-state model fit in nucleon structure calculations.

Findings

Excited state contamination can be modeled and reduced.

Varying source-sink separation helps identify systematic errors.

Two-state fit effectively subtracts excited state contributions.

Abstract

Among the sources of systematic error in nucleon structure calculations is contamination from unwanted excited states. In order to measure this systematic error, we vary the operator insertion time and source-sink separation independently. We compute observables for three source-sink separations between 0.93 fm and 1.39 fm using clover-improved Wilson fermions and pion masses as low as 150 MeV. We explore the use of a two-state model fit to subtract off the contribution from excited states.