A measurement of the time profile of scintillation induced by low energy gamma-rays in liquid xenon with the XMASS-I detector

TL;DR

This study measures the scintillation time profile in liquid xenon caused by low-energy gamma-rays, revealing energy-dependent decay times and a fast component, which are crucial for dark matter detection.

Contribution

First measurement of gamma-ray induced scintillation time profiles in liquid xenon at low energies relevant to dark matter searches, including detailed energy dependence analysis.

Findings

Decay time constant increases from 27.9 ns to 37.0 ns with gamma-ray energy.

A fast decay component with approximately 2 ns decay time is essential.

Results extend previous measurements to lower energies relevant for dark matter detection.

Abstract

We report the measurement of the emission time profile of scintillation from gamma-ray induced events in the XMASS-I 832 kg liquid xenon scintillation detector. Decay time constant was derived from a comparison of scintillation photon timing distributions between the observed data and simulated samples in order to take into account optical processes such as absorption and scattering in liquid xenon. Calibration data of radioactive sources, $^{55}$Fe, $^{241}$Am, and $^{57}$Co were used to obtain the decay time constant. Assuming two decay components, $\tau_1$ and $\tau_2$, the decay time constant $\tau_2$ increased from 27.9 ns to 37.0 ns as the gamma-ray energy increased from 5.9 keV to 122 keV. The accuracy of the measurement was better than 1.5 ns at all energy levels. A fast decay component with $\tau_1 \sim 2$ ns was necessary to reproduce data. Energy dependencies of $\tau_2$ and the fraction of the fast decay component were studied as a function of the kinetic energy of electrons induced by gamma-rays. The obtained data almost reproduced previously reported results and extended them to the lower energy region relevant to direct dark matter searches.