First Limit on the Direct Detection of Lightly Ionizing Particles for Electric Charge as Low as $e$/1000 with the \textsc{Majorana Demonstrator}

TL;DR

This paper reports the first direct detection limits on lightly ionizing particles with charges as low as e/1000, using the Majorana Demonstrator's low-background germanium detectors over 285 days.

Contribution

It provides the first experimental limits on the flux of lightly ionizing particles with very small charges using a low-background germanium detector array.

Findings

No candidate events were observed in 285 days.

New flux limits for particles with charges as low as e/1000 were established.

The search demonstrates the detector's sensitivity to low-energy depositions from exotic particles.

Abstract

The \textsc{Majorana Demonstrator} is an ultra low-background experiment searching for neutrinoless double-beta decay in $^{76}$Ge. The heavily shielded array of germanium detectors, placed nearly a mile underground at the Sanford Underground Research Facility in Lead, South Dakota, also allows searches for new exotic physics. Free, relativistic, lightly-ionizing particles with electrical charges less than $e$ are forbidden by the standard model but predicted by some of its extensions. If such particles exist, they might be detected in the \textsc{Majorana Demonstrator} by searching for multiple- detector events with individual-detector energy depositions down to 1 keV. This search is background free and no candidate events have been found in 285 days of data taking. New direct-detection limits are set for the flux of lightly ionizing particles for charges as low as $e$/1000.