Highly Improved Staggered Quarks on the Lattice, with Applications to Charm Physics

TL;DR

The paper introduces the HISQ lattice action, significantly reducing taste-exchange errors and discretization errors, leading to more accurate charm quark simulations and precise mass splitting results.

Contribution

Development of the HISQ action with reduced taste-exchange and discretization errors, improving accuracy in charm quark lattice simulations.

Findings

Taste-exchange errors are 3-4 times smaller with HISQ than ASQTAD.

Taste-exchange errors are estimated to be no more than 1% at lattice spacings of 1/10 fm.

HISQ provides the most accurate discretization for simulating charm quarks, demonstrated by psi-eta_c mass splitting analysis.

Abstract

We use perturbative Symanzik improvement to create a new staggered-quark action (HISQ) that has greatly reduced one-loop taste-exchange errors, no tree-level order a^2 errors, and no tree-level order (am)^4 errors to leading order in the quark's velocity v/c. We demonstrate with simulations that the resulting action has taste-exchange interactions that are at least 3--4 times smaller than the widely used ASQTAD action. We show how to estimate errors due to taste exchange by comparing ASQTAD and HISQ simulations, and demonstrate with simulations that such errors are no more than 1% when HISQ is used for light quarks at lattice spacings of 1/10 fm or less. The suppression of (am)^4 errors also makes HISQ the most accurate discretization currently available for simulating c quarks. We demonstrate this in a new analysis of the psi-eta_c mass splitting using the HISQ action on lattices where a m_c=0.43 and 0.66, with full-QCD gluon configurations (from MILC). We obtain a result of~111(5) MeV which compares well with experiment. We discuss applications of this formalism to D physics and present our first high-precision results for D_s mesons.