Validating the Dark Matter Origin of a LDMX Signal with Direct Detection Experiments

Abstract

The search for a particle candidate explaining the origin of dark matter is one of the central goals in modern astro-particle physics. Many experiments based on different measurement strategies are being built in an effort to detect such a candidate. In the event that a dark matter signal is seen, it is crucial to verify the signal with other experiments. In this thesis we explore the possibility of using a direct detection experiment to validate a hypothetical dark matter signal seen at the Light Dark Matter eXperiment (LDMX). We consider a rep resentative light dark matter model with masses ranging between ∼ 1 − 1000 MeV, which are assumed to be mediated by a massive dark photon. Hypothetical dark matter signals are simulated, both for an LDMX-type experiment and for a semiconductor based direct detection experiment. These signals are generated for varying values of the “true" dark matter mass mχ,true and dark photon kinetic mixing εtrue parameters, which are chosen under thermal relic abundance constraints. Validation is achieved by using the MultiNest Monte Carlo algorithm to estimate the marginal posterior of the mχ and ε parameters given the hypothetical direct detection signal. The parameter estimate is input into the LDMX-type simulation software and compared with that of the hypothetical LDMX re sult. The chi-square hypothesis test is used to conclude whether the two distributions are consistent with a single distribution function. A conclusion is drawn regarding the amount of exposure required for a direct detection experiment to validate a hypothetical LDMX signal for some choices of mχ,true. For instance, when mχ,true = 10 MeV the threshold exposure for validation was determined to be 0.05 kg-year.