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Register a new userObservation of unusual slow components in electroluminescence signal of two-phase argon detector
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Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter search to record ionization signals in the gas phase induced by particle scattering in the liquid phase (S2 signals). In this work, the EL pulse-shapes in a two-phase argon detector have for the first time been studied systematically in a wide range of reduced electric field, varying from 3 to 9 Td. The pulse-shapes were studied at different readout configurations and spectral ranges: using cryogenic PMTs and SiPMs, with and without a wavelength shifter (WLS), in the VUV and visible range. We observed the fast component and two unusual slow components, with time constants of about 5 $mu$s and 40 $mu$s. The unusual characteristic property of slow components was that their contribution and time constants increased with electric field.
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Proportional electroluminescence (EL) in noble gases has long been used in two-phase detectors for dark matter search, to record ionization signals induced by particle scattering in the noble-gas liquid (S2 signals). Until recently, it was believed that proportional electroluminescence was fully due to VUV emission of noble gas excimers produced in atomic collisions with excited atoms, the latter being in turn produced by drifting electrons. In this work we consider an additional mechanism of proportional electroluminescence, namely that of bremsstrahlung of drifting electrons scattered on neutral atoms (so-called neutral bremsstrahlung); it is systemically studied here both theoretically and experimentally. In particular, the absolute EL yield has for the first time been measured in pure gaseous argon in the two-phase mode, using a dedicated two-phase detector with EL gap optically read out by cryogenic PMTs and SiPMs. We show that the neutral bremsstrahlung effect can explain two intriguing observations in EL radiation: that of the substantial contribution of the non-VUV spectral component, extending from the UV to NIR, and that of the photon emission at lower electric fields, below the Ar excitation threshold. Possible applications of neutral bremsstrahlung effect in two-phase dark matter detectors are discussed.
We further study the effect of neutral bremsstrahlung (NBrS) in two-phase argon electroluminescence (EL), revealed recently in [1]. The absolute EL yield due to NBrS effect, in the visible and NIR range, was remeasured in pure gaseous argon in the two-phase mode, using a two-phase detector with EL gap read out directly by cryogenic PMTs and SiPMs. Possible applications of the NBrS effect in detection science are discussed, including those in two-phase dark matter detectors.
Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The standard EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (neutral bremsstrahlung, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.
Proportional electroluminescence (EL) is the physical effect used in two-phase detectors for dark matter searches, to optically record (in the gas phase) the ionization signal produced by particle scattering in the liquid phase. In our previous work the presence of a new EL mechanism, namely that of neutral bremsstrahlung (NBrS), was demonstrated in two-phase argon detectors both theoretically and experimentally, in addition to the ordinary EL mechanism due to excimer emission. In this work the similar theoretical approach is applied to all noble gases, i.e. overall to helium, neon, argon, krypton and xenon, to calculate the EL yields and spectra both for NBrS and excimer EL. The relevance of the results obtained to the development of two-phase dark matter detectors is discussed.
We performed a time-resolved spectroscopic study of the VUV/UV argon scintillation as a function of pressure and electric field, by means of a wavelength sensitive detector operated with different radioactive sources. Our work conveys new evidence of distinctive features of the argon light which are in contrast with the general assumption that, for particle detection purposes, the scintillation can be considered to be largely monochromatic at 128 nm (second continuum). The wavelength and the time-resolved analysis of the photon emission reveal that the dominant component of the argon scintillation during first tens of ns is in the range [160, 325] nm. This light is consistent with the third continuum emission from highly charged argon ions/molecules. This component of the scintillation is field-independent up to 25 V/cm/bar and shows a very mild dependence with pressure in the range [1,16] bar. The dynamics of the second continuum emission is dominated by the excimer formation time, whose variation as a function of the pressure has been measured. Additionally, the time and pressure-dependent features of electron-ion recombination, in the second continuum band, have been measured. This study opens new paths toward a novel particle identification technique based on the spectral information of the noble-elements scintillation light.
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