Characterizing Dark Matter Signals with Missing Momentum Experiments

TL;DR

This paper discusses how fixed target missing-momentum experiments can effectively detect and characterize light dark matter and new particles by analyzing kinematic variables, especially transverse momentum, to distinguish models and measure particle properties.

Contribution

It introduces novel methods using kinematic variables and experimental parameters to measure properties of new particles and discriminate models in missing-momentum experiments.

Findings

Transverse momentum is a powerful tool for mass measurement.

Beam energy and polarization variations help identify interaction types.

Methods improve model discrimination compared to recoil energy alone.

Abstract

Fixed target missing-momentum experiments such as LDMX and M$^3$ are powerful probes of light dark matter and other light, weakly coupled particles beyond the Standard Model (SM). Such experiments involve $\sim$ 10 GeV beam particles whose energy and momentum are individually measured before and after passing through a suitably thin target. If new states are radiatively produced in the target, the recoiling beam particle loses a large fraction of its initial momentum, and no SM particles are observed in a downstream veto detector. We explore how such experiments can use kinematic variables and experimental parameters, such as beam energy and polarization, to measure properties of the radiated particles and discriminate between models if a signal is discovered. In particular, the transverse momentum of recoiling particles is shown to be a powerful tool to measure the masses of new radiated states, offering significantly better discriminating ability compared to the recoil energy alone. We further illustrate how variations in beam energy, polarization, and lepton flavor (i.e., electron or muon) can be used to disentangle the possible the Lorentz structure of the new interactions.