Invisible widths of heavy mesons

TL;DR

This paper revises the understanding of heavy meson invisible widths, showing they are dominated by four-neutrino decays rather than two-neutrino ones, significantly impacting experimental constraints on new physics.

Contribution

It demonstrates that standard model predictions for heavy meson invisible widths are underestimated and clarifies the dominant decay channels, affecting dark photon constraints.

Findings

Invisible widths are dominated by four-neutrino decays.

Standard model estimates underestimate widths by orders of magnitude.

Experimental data constrains dark photon properties.

Abstract

We revisit calculations of invisible widths of heavy mesons in the standard model, which serve as benchmarks for the studies of production of light, long-lived neutral particles in heavy meson decays. We challenge the common assumption that in the standard model these widths are dominated by meson decays into a two-neutrino final state and prove that they are dominated by decays into four-neutrino final states. We show that current estimates of the invisible widths of heavy mesons in the standard model underestimate the effect by orders of magnitude. We examine currently available experimental data on invisible widths and place constraints on the properties of dark photons. We also comment on the invisible widths of the kaons.