Search for Daily Modulation of MeV Dark Matter Signals with DAMIC-M

TL;DR

This study uses the DAMIC-M detector to search for daily modulation signals from MeV-scale dark matter interactions, setting new limits on such particles and improving previous constraints by two orders of magnitude.

Contribution

First underground search for daily modulation of MeV dark matter signals with DAMIC-M, providing the strongest limits on DM-electron interactions around 1 MeV/c².

Findings

No daily modulation detected in 1e- events.

Set exclusion limits on MeV-scale DM with dark photon mediators.

Improved previous limits by approximately 100 times.

Abstract

Dark Matter (DM) particles with sufficiently large cross sections may scatter as they travel through Earth's bulk. The corresponding changes in the DM flux give rise to a characteristic daily modulation signal in detectors sensitive to DM-electron interactions. Here, we report results obtained from the first underground operation of the DAMIC-M prototype detector searching for such a signal from DM with MeV-scale mass. A model-independent analysis finds no modulation in the rate of 1$e^-$ events with sidereal period, where a DM signal would appear. We then use these data to place exclusion limits on DM in the mass range [0.53, 2.7] MeV/c$^2$ interacting with electrons via a dark photon mediator. Taking advantage of the time-dependent signal we improve by $\sim$2 orders of magnitude on our previous limit obtained from the total rate of 1$e^-$ events, using the same data set. This daily modulation search represents the current strongest limit on DM-electron scattering via ultralight mediators for DM masses around 1 MeV/c$^2$.