Photon emission and atomic collision processes in two-phase argon doped with xenon and nitrogen

Abstract

PACS 95.55.Vj -Neutrino, muon,pion, and other elementary particle detectors; cosmic ray detectors PACS 61.25.Bi -Liquid noble gases PACS 95.35.+d -Dark matter Abstract -We present a comprehensive analysis of photon emission and atomic collision processes in two-phase argon doped with xenon and nitrogen. The dopants are aimed to convert the VUV emission of pure Ar to the UV emission of the Xe dopant in the liquid phase and to the near UV emission of the N2 dopant in the gas phase. Such a mixture is relevant to two-phase dark matter and low energy neutrino detectors, with enhanced photon collection efficiency for primary and secondary scintillation signals. Based on this analysis, we show that the recently proposed hypothesis of the enhancement of the excitation transfer from Ar to N2 species in the two-phase mode is either incorrect or needs assumption about a new extreme mechanism of the excitation transfer coming into force at lower temperatures, in particular that of the resonant excitation transfer via ArN2 compound (van der Waals molecule).

Fast component re-emission in Xe-doped liquid argon

“…Other scintillation signal parameters are in agreement with the previous results [18][19][20]: as Xe concentration grows, the light yield increases, and the energy resolution becomes slightly better ( figure 9). According to our data, the light yield saturates when Xe concentration reaches the point of the total re-emission of the fast component by Xe.…”

“…This improves position reconstruction since the re-emission occurs in the point of interaction.It was shown that gaseous xenon doped in LAr works as a volume-distributed WLS shifting the wave length from 128 nm to around 175 nm [14][15][16]. Currently several groups are studying its wavelength shifting parameters and the properties of the LAr+Xe mixture [17][18][19][20]. As shown previously [21], Xe doped in small concentrations (up to 260 ppm by mass) re-emits only the slow component of LAr scintillation.…”

Neutral bremsstrahlung in two-phase argon electroluminescence: further studies and possible applications

“…The effect of proportional electroluminescence (EL) in noble gases [2,3] has long been used in two-phase detectors to record ionization signals in the gas phase, induced by particle scattering in the liquid phase (so-called S2 signals) [4,5]. Such two-phase detectors are relevant for dark matter search and lowenergy neutrino detection.…”

“…Ar * 2 ( 1,3 Σ + u ), produced in three-body atomic collisions with excited atoms, e.g. Ar * (3p 5 4s 1 ), which in turn are produced by drifting electrons in electron-atom collisions: see review [3]. In the case of Ar this results in almost mandatory use of a wavelength shifter (WLS) in front of PMTs and SiPMs, to convert the VUV emission into the visible light [5].…”

Electron transport and electric field simulations in two-phase detectors with THGEM electrodes

“…Two-phase detectors with electroluminescence (EL) gap, based on Ar and Xe, are relevant to experiments for direct search of dark matter particles [1,2]. Several versions of such detectors were developed in our laboratory for the study of EL mechanism in pure argon [3] and argon doped with nitrogen [4,5], for SiPM-matrix readout of two-phase detectors, directly [6] or using combined THGEM/SiPM-matrix multipliers [6,7,8], and for the measurements of ionization yields in liquid argon [9]. One of the main features of two-phase detectors developed in our laboratory is the extensive use of THGEMs (Thick Gas Electron Multipliers [10]).…”