Kinematic Cusps With Two Missing Particles I: Antler Decay Topology

TL;DR

This paper analyzes the kinematic cusp structures in antler decay topologies with two missing particles, deriving analytic formulas and exploring their use in mass determination, considering realistic effects like decay widths and boosts.

Contribution

It provides the first comprehensive analytic expressions for invariant mass cusps in antler decay topologies, including effects of finite widths and boosts.

Findings

Kinematic cusps are sharp and prominent in various distributions.

Analytic formulas for cusp positions and endpoints are derived.

Realistic effects like decay widths and boosts influence cusp structures.

Abstract

The kinematics of a final state system with two invisible particles and two visible particles can develop cusped peak structures. This happens when the system has a fixed invariant mass (such as from a narrow resonant particle decay or with a fixed collision c.m. energy) and undergoes decays of two on-shell intermediate particles. Focusing on the "antler decay topology", we derive general analytic expressions for the invariant mass distribution and the kinematic cusp position. The sharp cusp peaks and the endpoint positions can help to determine the masses of the missing particles and the intermediate particles. We also consider transverse momentum variables and angular variables. In various distributions the kinematic cusp peaks are present and pronounced. We also study the effects on such kinematic cusp structures from realistic considerations including finite decay widths, the longitudinal boost of the system, and spin correlations.