Possible evidence for the production of Ar${}_2^{\ast -}$ metastable negative molecular ions in gaseous argon of two-phase detectors for dark matter searches

Abstract

Our recent studies of electroluminescence (EL) properties in two-phase argon detectors for dark matter searches have revealed the presence of unusual delayed pulses in the EL signal in the form of two slow components with time constants of about 5 and 50 $\mu$s. These components were shown to be present in the charge signal itself, which clearly indicates that drifting electrons are temporarily trapped on two states of metastable negative argon ions which have never been observed before. In this work, using the pressure dependence of the ratio of slow component contributions measured in experiment, it is deduced that these states are those of two types of metastable negative molecular ions, ${\mathrm{Ar}}_2^{\ast -}(b{}^4{\Sigma }_u^{-})$ and ${\mathrm{Ar}}_2^{\ast -}(a{}^4{\Sigma }_g^{+})$ for the higher and lower energy level respectively.

4 pages, 2 figures

References in corpus (11)

• Excess Electronic Recoil Events in XENON1T
• Emission of Single and Few Electrons in XENON1T and Limits on Light Dark Matter
• Electroluminescence and electron avalanching in two-phase detectors
• Photon emission and atomic collision processes in two-phase argon doped with xenon and nitrogen
• Neutral Bremsstrahlung emission in xenon unveiled
• Neutral bremsstrahlung electroluminescence in noble liquids
• Neutral bremsstrahlung and excimer electroluminescence in noble gases and its relevance to two-phase dark matter detectors
• Bremsstrahlung on noble gases at low energies
• Puzzling time properties of proportional electroluminescence in two-phase argon detectors for dark matter searches
• Observation of unusual slow components in electroluminescence signal of two-phase argon detector
• Unraveling the puzzle of slow components in gaseous argon of two-phase detectors for dark matter searches using Thick Gas Electron Multiplier