Abstract
The proposed LDMX experiment would provide roughly a meter-long region of instrumented tracking and calorimetry that acts as a beam stop for multi-GeV electrons in which each electron is tagged and its evolution measured. This would offer an unprecedented opportunity to access both collider-invisible and ultra-short lifetime decays of new particles produced in electron (or muon)-nuclear fixed-target collisions. In this paper, we show that the missing momentum channel and displaced decay signals in such an experiment could provide world-leading sensitivity to sub-GeV dark matter, millicharged particles, and visibly or invisibly decaying axions, scalars, dark photons, and a range of other new physics scenarios.
Highlights
Particle dark matter (DM) science is undergoing a revolution, driven simultaneously by recent advances in theory and experiment
We investigated a broad range of sub-GeV dark sector scenarios and evaluated the sensitivity of small-scale accelerator experiments and applicable direct detection efforts
Our focus was on the keV–GeV mass range, and our primary goal was to understand the range of new physics sensitivity provided by the inclusive missing momentum measurement proposed by the acceleratorbased Light Dark Matter eXperiment (LDMX)
Summary
Particle dark matter (DM) science is undergoing a revolution, driven simultaneously by recent advances in theory and experiment. The detector concept allows each individual electron to be tagged and its evolution measured as it passes through a thin target, tracking planes, and a high-granularity silicon-tungsten calorimeter Does this enable a model-independent missing momentum and energy search, but it offers an unprecedented opportunity to access remarkably shortlifetime (cτ ∼ 10 μm) decays of new particles. We find that sensitivity to the invisible decays of dark photons and minimal gauged B − L (and Li − Lj, B − 3Li) symmetries will be enhanced by many orders of magnitude compared to existing searches in the entire sub-GeV mass range, and cover unexplored parameter space that can address the ðg − 2Þμ anomaly.
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