Ultra-Low Energy Calibration of LUX Detector using $^{127}$Xe Electron Capture

TL;DR

This paper presents a precise calibration of ionization yields for low-energy electronic recoils in liquid xenon using $^{127}$Xe decay events, enabling better understanding of detector responses at energies as low as 186 eV.

Contribution

It introduces the first in situ measurement of electronic recoil ionization yields at energies down to 186 eV in liquid xenon using $^{127}$Xe electron capture decays.

Findings

Verified ratio of cascade events matches calculations across shells.

Achieved lowest-energy electronic recoil measurements in liquid xenon.

Provided calibration data for energies as low as 186 eV.

Abstract

We report an absolute calibration of the ionization yields($\textit{Q$_y$})$ and fluctuations for electronic recoil events in liquid xenon at discrete energies between 186 eV and 33.2 keV. The average electric field applied across the liquid xenon target is 180 V/cm. The data are obtained using low energy $^{127}$Xe electron capture decay events from the 95.0-day first run from LUX (WS2013) in search of Weakly Interacting Massive Particles (WIMPs). The sequence of gamma-ray and X-ray cascades associated with $^{127}$I de-excitations produces clearly identified 2-vertex events in the LUX detector. We observe the K- (binding energy, 33.2 keV), L- (5.2 keV), M- (1.1 keV), and N- (186 eV) shell cascade events and verify that the relative ratio of observed events for each shell agrees with calculations. The N-shell cascade analysis includes single extracted electron (SE) events and represents the lowest-energy electronic recoil $\textit{in situ}$ measurements that have been explored in liquid xenon.