-event characterization and rejection in point-contact HPGe detectors

Area of Science:

• Nuclear physics
• Particle physics
• Detector technology

Background:

• P-type Point Contact (PPC) High Purity Germanium (HPGe) detectors are crucial for rare event searches.
• Understanding background events on detector surfaces is vital for experimental sensitivity.
• Previous characterization of surface backgrounds in PPC HPGe detectors was limited.

Purpose of the Study:

• To characterize the response of PPC HPGe detectors to alpha particles on their surfaces.
• To investigate the phenomenon of charge trapping and Delayed Charge Recovery (DCR).
• To develop and validate a new method for background event rejection.

Main Methods:

• Utilized a PPC HPGe detector identical to those in the Majorana Demonstrator experiment.
• Studied alpha particle interactions on the detector's passivated and p+ surfaces.
• Analyzed detector waveforms to identify DCR signatures.
• Combined DCR discrimination with existing background rejection techniques.

Main Results:

• Alpha decays on the passivated surface exhibit energy loss and DCR due to charge trapping.
• DCR provides a complementary method for identifying surface alpha background events.
• Effective rejection of all surface alpha events was achieved with minimal loss (0.2%) of bulk events.
• DCR discriminator reduced background rates by an order of magnitude in the Majorana Demonstrator.

Conclusions:

• DCR is a powerful tool for identifying and rejecting surface alpha backgrounds in PPC HPGe detectors.
• This method enhances the sensitivity of rare event searches by reducing background.
• The DCR discriminator will be implemented in future experiments like LEGEND-200.