HQET sum rules for matrix elements of dimension-six four-quark operators for meson lifetimes within and beyond the Standard Model

TL;DR

This paper uses HQET sum rules to calculate non-perturbative matrix elements of four-quark operators affecting meson lifetimes, including BSM contributions, improving theoretical predictions of B meson lifetime ratios.

Contribution

First non-perturbative determination of four-quark operator matrix elements for B meson lifetimes within and beyond the Standard Model using HQET sum rules.

Findings

Computed matrix elements for BSM operators affecting meson lifetimes.

Updated bag parameters for Standard Model operators.

Enhanced precision in theoretical B meson lifetime ratio predictions.

Abstract

Theory predictions of heavy-hadron lifetime ratios critically depend on precise determinations of the dimension-six spectator effects arising from the double insertion of the weak effective $|\Delta B| = 1$ Hamiltonian. In the presence of beyond-standard-model (BSM) operators, the resulting $\Delta B = 0$ Hamiltonian features additional four-quark operators whose matrix elements need to be determined using non-perturbative methods. We present for the first time results for the non-perturbative hadronic matrix elements of the four-quark operators relevant for the description of the meson lifetime ratio $\tau\left(B^+\right) / \tau\left(B_d\right)$, obtained using heavy-quark effective theory (HQET) sum rules with the full BSM effective Hamiltonian. In addition, we recompute and update the bag parameters for the Standard Model operators.