Calibration of the NEXT-White detector using ^83mKr decays

Abstract

The NEXT-White (NEW) detector is currently the largest radio-pure high-pressure xenon gas time projection chamber with electroluminescent readout in the world. It has been operating at Laboratorio Subterr'aneo de Canfranc (LSC) since October 2016. This paper describes the calibrations performed using 83mKr decays during a long run taken from March to November 2017 (Run II). Krypton calibrations are used to correct for the finite drift-electron lifetime as well as for the dependence of the measured energy on the event transverse position which is caused by variations in solid angle coverage both for direct and reflected light and edge effects. After producing calibration maps to correct for both effects we measure an excellent energy resolution for 41.5 keV point-like deposits of (4.553 ± 0.010 (stat) ± 0.324 (sys))% FWHM in the full chamber and (3.804 ± 0.013 (stat) ± 0.112 (sys))% FWHM in a restricted fiducial volume. Using naive 1/√E scaling, these values translate into resolutions of (0.5916 ± 0.0014 (stat) ± 0.0421 (sys))% FWHM and (0.4943 ± 0.0017 (stat) ± 0.0146 (sys))% FWHM at the Qββ energy of xenon double beta decay (2458 keV), well within range of our target value of 1%.

Demonstration of the event identification capabilities of the NEXT-White detector

“…The electron lifetime was measured continuously using a 83m Kr source diffused homogeneously in the gas and the collected charge at the PMT plane was corrected for it (for a detailed description of the NEXT-White calibration procedure, see ref. [12]). The average value of the electron lifetime was quite stable across the different runs, around 4.5 ms, several times larger than the full-chamber drift time.…”

Neutrinoless double beta decay overview

“…As a consequence, the collaboration decided to deploy the NEW (NEXT-WHITE) apparatus (scale 1:2 in size, or 1:8 in mass of NEXT-100). Preliminary results obtained with this apparatus indicate a satisfactory radio-purity and an energy resolution of (0.4943±0.0017(stat)±0.0146(sys))% FWHM at the Q-value in the fiducial volume [35].…”

Electron drift properties in high pressure gaseous xenon

“…Our data hints towards 7.2 bar D T results being somewhat higher than the 9.1 bar bar D T ones. The cause of the discrepancy remains to be studied in detail although it may be related to the lifetime dependence with the transverse position that has been observed in the 7.2 bar data but not in the 9.1 bar one, as stated in [26]. The irregular lifetime may affect the charge distribution of the SiPMs having an effect in the outcome of the sensor's charge cut, which was fixed for the all the datasets.…”