New Measurements with Stopped Particles at the LHC

TL;DR

This paper explores how observing out-of-time decays of stopped metastable particles at the LHC can reveal detailed properties of new physics particles, including charge, spin, decay modes, and Lorentz structure, with a small number of observed events.

Contribution

It introduces strategies for measuring decay types, particle properties, and decay operator structures from stopped particle decays at the LHC, providing insights into high-scale physics.

Findings

Decay properties can be measured with 10-100 events.

The Lorentz structure of decay operators can be distinguished.

Particle charge, spin, and decay modes can be inferred.

Abstract

Metastable particles are common in many models of new physics at the TeV scale. If charged or colored, a reasonable fraction of all such particles produced at the LHC will stop in the detectors and give observable out of time decays. We demonstrate that significant information may be learned from such decays about the properties (e.g. charge or spin) of this particle and of any other particles to which it decays, for example a dark matter candidate. We discuss strategies for measuring the type of decay (two- vs three-body), the types of particles produced, and the angular distribution of the produced particles using the LHC detectors. We demonstrate that with O(10-100) observed decay events, not only can the properties of the new particles be measured but indeed even the Lorentz structure of the decay operator can be distinguished in the case of three-body decays. These measurements can not only reveal the correct model of new physics at the TeV scale, but also give information on physics giving rise to the decay at energy scales far above those the LHC can probe directly.