Searches for new physics below twice the electron mass with GERDA

Area of Science:

• Particle Physics
• Cosmology
• Astrophysics

Background:

• Dark matter remains a significant mystery in physics.
• Bosonic dark matter candidates, such as dark photons and axion-like particles, are actively researched.
• The GERDA experiment is designed to detect rare interactions of particles with germanium detectors.

Purpose of the Study:

• To search for keV-scale bosonic dark matter using Phase II data from the GERDA experiment.
• To set direct exclusion limits on the properties of dark matter candidates.
• To search for beyond Standard Model decays of nucleons and electrons.

Main Methods:

• Analysis of full energy depositions from 105.5 kg-years of GERDA Phase II data.
• Inclusion of direct dark matter absorption and dark Compton scattering signals.
• Application of Bayesian and Frequentist statistical methods to derive exclusion limits.
• Searched for peak-like signals indicative of nucleon and electron decays.

Main Results:

• No evidence for a dark matter signal was observed above background.
• The most stringent direct constraints on dark matter candidates (dark photons, axion-like particles) were set for masses between 140-1021 keV.
• Lower lifetime limits were established for neutron, proton, and electron decays.

Conclusions:

• The GERDA experiment has significantly advanced the search for light bosonic dark matter.
• The results provide crucial direct constraints, narrowing the parameter space for various dark matter models.
• The study also placed strong limits on hypothetical beyond Standard Model particle decays.