Enhanced Signal and Excited-State Control in Nonlocal Lattice Correlators

Abstract

Nonlocal correlation functions underpin lattice calculations of parton physics. However, their extraction is limited by a rapidly deteriorating signal-to-noise ratio with increasing Euclidean separation and hadron momentum, and by excited-state contamination. We propose a new fitting strategy that enhances control over both: by taking the ratio of nonlocal to local correlators, we can project out the dominant ground-state dynamics with a signal that is much cleaner and far less sensitive to excited states than the conventional approach. We demonstrate the method on the quark and gluon PDF, the quark GPD and TMDPDF. The results are consistent with those from the conventional three-point/two-point ratio fit but exhibit markedly improved precision and stability, and extend the accessible range to larger hadron momenta. For nonforward matrix elements such as GPDs, our strategy greatly simplifies the analysis procedure. Our method applies to general Dirac and momentum structures, for connected and disconnected contributions, and extends naturally to other nonlocal correlators, making it immediately deployable in existing lattice programs toward precision hadron structure.