Probing resonance decays to two visible and multiple invisible particles

TL;DR

This paper analyzes how the invariant mass distribution of visible particles from a resonance decay reveals information about the mass spectrum and decay topology, aiding in particle identification.

Contribution

It provides analytical formulas for invariant mass shapes for nine decay topologies with up to two invisible particles, enabling topology discrimination and mass spectrum determination.

Findings

Invariant mass shape depends on decay topology and mass spectrum.

Endpoint, peak, and curvature characterize the invariant mass distribution.

In some cases, the shape fully determines the new particle masses.

Abstract

We consider the decay of a generic resonance to two visible particles and any number of invisible particles. We show that the shape of the invariant mass distribution of the two visible particles is sensitive to both the mass spectrum of the new particles, as well as the decay topology. We provide the analytical formulas describing the invariant mass shapes for the nine simplest topologies (with up to two invisible particles in the final state). Any such distribution can be simply categorized by its endpoint, peak location and curvature, which are typically sufficient to discriminate among the competing topologies. In each case, we list the effective mass parameters which can be measured by experiment. In certain cases, the invariant mass shape is sufficient to completely determine the new particle mass spectrum, including the overall mass scale.