A High Efficiency Photon Veto for the Light Dark Matter eXperiment

Understand

Fixed-target experiments using primary electron beams can be powerful discovery tools for light dark matter in the sub-GeV mass range.

• The Light Dark Matter eXperiment (LDMX) is designed to measure missing momentum in high-rate electron fixed-target reactions with beam energies of 4 GeV to 16 GeV.
• A prerequisite for achieving several important sensitivity milestones is the capability to efficiently reject backgrounds associated with few-GeV bremsstrahlung, by twelve orders of magnitude, while maintaining high efficiency for signal.
• The primary challenge arises from events with photo-nuclear reactions faking the missing-momentum property of a dark matter signal.