First constraint for atmospheric millicharged particles with the LUX-ZEPLIN experiment

TL;DR

This paper reports the first search for atmospheric millicharged particles using the LUX-ZEPLIN liquid xenon detector, setting new constraints on their properties with no significant detection.

Contribution

It introduces a novel detection method for millicharged particles in liquid xenon TPCs and provides the first experimental constraints on atmospheric mCPs in this context.

Findings

No significant excess observed over background.

Set new upper limits on mCP flux and charge fraction.

Demonstrated the feasibility of underground liquid xenon detectors for mCP searches.

Abstract

We report on a search for millicharged particles (mCPs) produced in cosmic ray proton atmospheric interactions using data collected during the first science run of the LUX-ZEPLIN experiment. The mCPs produced by two processes -- meson decay and proton bremsstrahlung -- are considered in this study. This search utilized a novel signature unique to liquid xenon (LXe) time projection chambers (TPCs), allowing sensitivity to mCPs with masses ranging from 10 to 1000 MeV/c$^2$ and fractional charges between 0.001 and 0.02 of the electron charge e. With an exposure of 60 live days and a 5.5 tonne fiducial mass, we observed no significant excess over background. This represents the first experimental search for atmospheric mCPs and the first search for mCPs using an underground LXe experiment.