Ion-beam excitation of liquid argon

TL;DR

This study provides detailed wavelength and time-resolved scintillation data of liquid argon excited by various ion beams, demonstrating particle discrimination capabilities based on the singlet-to-triplet ratio.

Contribution

It offers new insights into the scintillation characteristics of liquid argon with different ions and confirms the effectiveness of the singlet-to-triplet ratio for particle discrimination at low energies.

Findings

Minor differences in wavelength spectra across ion types

Suppression of third excimer continuum in liquid phase

Discrimination threshold as low as 2.5 keV for protons vs sulfur ions

Abstract

The scintillation light of liquid argon has been recorded wavelength and time resolved with very good statistics in a wavelength interval ranging from 118 nm through 970 nm. Three different ion beams, protons, sulfur ions and gold ions, were used to excite liquid argon. Only minor differences were observed in the wavelength-spectra obtained with the different incident particles. Light emission in the wavelength range of the third excimer continuum was found to be strongly suppressed in the liquid phase. In time-resolved measurements, the time structure of the scintillation light can be directly attributed to wavelength in our studies, as no wavelength shifter has been used. These measurements confirm that the singlet-to-triplet intensity ratio in the second excimer continuum range is a useful parameter for particle discrimination, which can also be employed in wavelength-integrated measurements as long as the sensitivity of the detector system does not rise steeply for wavelengths longer than 190 nm. Using our values for the singlet-to-triplet ratio down to low energies deposited a discrimination threshold between incident protons and sulfur ions as low as $\sim$2.5 keV seems possible, which represents the principle limit for the discrimination of these two species in liquid argon.