First Direct-Detection Results on Sub-GeV Dark Matter Using the SENSEI Detector at SNOLAB.

Area of Science:

• Particle Physics
• Astrophysics
• Cosmology

Background:

• Dark matter remains one of the most significant mysteries in modern physics.
• Direct detection experiments aim to observe dark matter particles interacting with ordinary matter.
• Sub-GeV dark matter candidates are particularly challenging to detect due to their low energy interactions.

Purpose of the Study:

• To present the first results from a dark matter search using Skipper-CCDs.
• To set world-leading constraints on sub-GeV dark matter.
• To explore dark matter interactions with both electrons and nuclei.

Main Methods:

• Utilized six Skipper-Charge Coupled Devices (CCDs) in the SENSEI detector at SNOLAB.
• Implemented a bias-mitigation technique involving data hiding and aggressive image masking to reduce backgrounds.
• Achieved a total exposure of 100.72 gram-days from well-performing sensors.

Main Results:

• Observed 55 two-electron events, consistent with pileup from one-electron events.
• Detected 4 three-electron events, with 2 potentially linked to detector defects.
• Found no events with 4-10 electrons, setting limits on potential signals.

Conclusions:

• The observed events are consistent with known backgrounds and detector effects.
• The experiment successfully established world-leading constraints for sub-GeV dark matter searches.
• Future analyses can refine these constraints with improved detector performance and analysis techniques.