Abstract
Detectors using liquid xenon as target are widely deployed in rare event searches. Conclusions on the interacting particle rely on a precise reconstruction of the deposited energy which requires calibrations of the energy scale of the detector by means of radioactive sources. However, a microscopic calibration, i.e. the translation from the number of excitation quanta into deposited energy, also necessitates good knowledge of the energy required to produce single scintillation photons or ionisation electrons in liquid xenon. The sum of these excitation quanta is directly proportional to the deposited energy in the target. The proportionality constant is the mean excitation energy and is commonly known as W-value. Here we present a measurement of the W-value with electronic recoil interactions in a small dual-phase xenon time projection chamber with a hybrid (photomultiplier tube and silicon photomultipliers) photosensor configuration. Our result is based on calibrations at mathcal {O}(1{-}10,{hbox {keV}}) with internal {^{37}hbox {Ar}} and {^{83text {m}}hbox {Kr}} sources and single electron events. We obtain a value of W={11.5}{} , ^{+0.2}_{-0.3} , mathrm {(syst.)} , hbox {eV}, with negligible statistical uncertainty, which is lower than previously measured at these energies. If further confirmed, our result will be relevant for modelling the absolute response of liquid xenon detectors to particle interactions.
Highlights
- value with electronic recoil interactions in a small dual-phase xenon time projection chamber with a hybrid photosensor configuration
In partica e-mail: kevin.thieme@physik.uzh.ch ular, time projection chambers (TPCs) operated in dual-phase mode with a gaseous xenon (GXe) layer at the top are among the leading technologies in the past, present and near-future hunt for WIMPs [10,11,12,13,14,15,16]
A particle that deposits energy in Liquid xenon (LXe) yields scintillation photons in the vacuum-ultraviolet (VUV) range with a peak centred at 175–178 nm wavelength [17,18], ionisation electrons and heat via atomic motion, where only the former two processes are detectable with dual-phase TPCs
Summary
A particle that deposits energy in LXe yields scintillation photons in the vacuum-ultraviolet (VUV) range with a peak centred at 175–178 nm wavelength [17,18], ionisation electrons and heat via atomic motion, where only the former two processes are detectable with dual-phase TPCs. Electrons that do not recombine are vertically drifted and extracted to the gas phase, by means of an electric drift and extraction field, where they collide with xenon atoms. In this process, a secondary proportional scintillation signal (S2) is produced by electroluminescence which is detected by photosensors. The W -value can be regarded as the average energy needed to produce a single free quantum in LXe and the above expression as its defining equation It determines the underlying recombination-independent energy scale in a LXe detector that detects both scintillation light and ionisation charge. The deviation of the EXO-200 value from former measurements motivated this study at keV-scale energies, deploying internal 37Ar and 83mKr sources.
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