A dual-phase xenon TPC for scintillation and ionisation yield measurements in liquid xenon

Abstract

A small-scale, two-phase (liquid/gas) xenon time projection chamber ( Xurich II ) was designed, constructed and is under operation at the University of Zürich. Its main purpose is to investigate the microphysics of particle interactions in liquid xenon at energies below 50 keV, which are relevant for rare event searches using xenon as target material. Here we describe in detail the detector, its associated infrastructure, and the signal identification algorithm developed for processing and analysing the data. We present the first characterisation of the new instrument with calibration data from an internal Kr source. The zero-field light yield is 15.0 and 14.0 photoelectrons/keV at 9.4 and 32.1 keV, respectively, and the corresponding values at an electron drift field of 1 kV/cm are 10.8 and 7.9 photoelectrons/keV. The charge yields at these energies are 28 and 31 electrons/keV, with the proportional scintillation yield of 24 photoelectrons per one electron extracted into the gas phase, and an electron lifetime of 200 s. The relative energy resolution, , is 11.9 and 5.8% at 9.4 and 32.1 keV, respectively using a linear combination of the scintillation and ionisation signals. We conclude with measurements of the electron drift velocity at various electric fields, and compare these to literature values.

The first dual-phase xenon TPC equipped with silicon photomultipliers and characterisation with $$^{37}\hbox {Ar}$$

“…We extract the electron drift speed for a given electric field from the clearly visible position of the cathode and the gate in the drift time histogram and their spatial separation. The procedure, together with a drift speed measurement at different fields in Xurich II, are detailed in [15]. The drift speeds that we find here are in agreement with this former measurement and are in the range 1.5-2.0 mm/µs.…”

“…The gain of the photosensors was monitored and calibrated about once a week with light from an external blue LED as described in [15]. The gain values are calculated following the model-independent approach proposed in [30].…”

“…Motivated by these future experiments, and by our previous studies of VUV-sensitive SiPM arrays in single-phase detectors [14], we have built and characterised the first dualphase xenon TPC equipped with a top photosensor array containing 16 SiPM channels read out individually. The new detector is based on our previously described Xurich II TPC [15], with several modifications as detailed below. The calibration of the detector, i.e.…”

“…7. The current TPC is an upgrade of the Xurich II detector operated at the University of Zurich (UZH) and described in [15]. The upgrade focuses on two aspects: the replacement of the top PMT with an array of SiPMs and their read-out electronics, and the design of a stand-alone setup to introduce the gaseous 37 Ar calibration source into the xenon recirculation loop.…”

“…The xenon is continuously purified of electronegative impurities by circulating the gas phase through a hot metal getter, an integral part of the gas handling system. The gas system features a source chamber which allows for the introduction of 83m Kr from the decay of 83 Rb with T 1/2 = 86.2(1) d [15,16]. With an additional gas mixing setup, described in Sect.…”