$B\pi$-state contamination in $B$-meson observables

TL;DR

This paper uses heavy meson chiral perturbation theory to quantify the impact of $B extpi$ states on lattice $B$-meson observables, revealing a few percent overestimation due to excited-state contamination.

Contribution

It introduces a method to calculate $B extpi$ contamination in $B$-meson observables using chiral perturbation theory at next-to-leading order.

Findings

$B extpi$ states cause a few percent overestimation of observables.

The contamination depends on unknown NLO low-energy coefficients.

A proposed strategy to measure one coefficient independently.

Abstract

Multi-particle states with additional pions are expected to result in a non-negligible excited-state contamination in lattice simulations. We show that heavy meson chiral perturbation theory can be employed to calculate the contamination due to two-particle $B\pi$ states in various $B$-meson observables like the $B$-meson decay constant and the $BB^*\pi$ coupling. We work in the static limit and to next-to-leading order in the chiral expansion. The $B\pi$ states are found to typically overestimate the observables at the few percent level depending on the size of two currently unknown NLO low-energy coefficients. A strategy to independently measure one of them with the 3-point function of the light axial vector current will be discussed.