The two-pion contribution to the hadronic vacuum polarization with staggered quarks

TL;DR

This paper reports the first lattice QCD calculation of two-pion contributions to the hadronic vacuum polarization using staggered quarks, achieving improved statistical precision for the muon's anomalous magnetic moment.

Contribution

It introduces a novel lattice QCD approach to compute two-pion contributions with enhanced accuracy, surpassing traditional noise-reduction methods.

Findings

Approximately threefold improvement in statistical precision.

Successful comparison with traditional noise-reduction techniques.

Foundation laid for future calculations at finer lattice spacings.

Abstract

We present results from the first lattice QCD calculation of the two-pion contributions to the light-quark connected vector-current correlation function obtained from staggered-quark operators. We employ the MILC collaboration's gauge-field ensemble with $2+1+1$ flavors of highly improved staggered sea quarks at a lattice spacing of $a\approx 0.15$ fm with a light sea-quark mass at its physical value. The two-pion contributions allow for a refined determination of the noisy long-distance tail of the vector-current correlation function, which we use to compute the light-quark connected contribution to HVP with improved statistical precision. We compare our results with traditional noise-reduction techniques used in lattice QCD calculations of the light-quark connected HVP, namely the so-called fit and bounding methods. We observe a factor of roughly three improvement in the statistical precision in the determination of the HVP contribution to the muon's anomalous magnetic moment over these approaches. We also lay the group theoretical groundwork for extending this calculation to finer lattice spacings with increased numbers of staggered two-pion taste states.