Characterisation of NEXT-DEMO using xenon K_αX-rays

Abstract

The NEXT experiment aims to observe the neutrinoless double beta decay of 136 Xe in a high-pressure xenon gas TPC using electroluminescence (EL) to amplify the signal from ionization. Understanding the response of the detector is imperative in achieving a consistent and well understood energy measurement. The abundance of xenon K-shell X-ray emission during data taking has been identified as a multitool for the characterisation of the fundamental parameters of the gas as well as the equalisation of the response of the detector. The NEXT-DEMO prototype is a ∼1.5 kg volume TPC filled with natural xenon. It employs an array of 19 PMTs as an energy plane and of 256 SiPMs as a tracking plane with the TPC light tube and SiPM surfaces being coated with tetraphenyl butadiene (TPB) which acts as a wavelength shifter for the VUV scintillation light produced by xenon. This paper presents the measurement of the properties of the drift of electrons in the TPC, the effects of the EL production region, and the extraction of position dependent correction constants using K α X-ray deposits. These constants were used to equalise the response of the detector to deposits left by gammas from 22 Na.-2 -

Sensitivity of NEXT-100 to neutrinoless double beta decay

“…This detector, named NEXT-100, possesses two features of great value for 0νββ-decay searches: excellent energy resolution (<1% FWHM at 2.5 MeV) [12,13] and charged-particle tracking for the active suppression of background [14,15]. Furthermore, the technology can be extrapolated to large source masses, thus allowing the full exploration of the inverted-hierarchy region of neutrino masses.…”

“…An energy resolution of 1% FWHM at 662 keV, which -assuming a 1/ √ E dependence -extrapolates to 0.5% FWHM at the Q value of 136 Xe, was measured in the DBDM prototype [12]. The best resolution measured in DEMO, 1.62% FWHM at 511 keV, extrapolates to 0.74% FWHM [13]. In addition, the NEXT-DEMO prototype has shown that track reconstruction is possible with an EL-based amplification scheme [14] and that the reconstructed energydeposition pattern can be used for the identification of signal-like and background-like event topologies [15].…”

“…The total energy deposited in the active volume was smeared according to the detector's energy-resolution function (0.75% FWHM at the Q value of 136 Xe); the energy accumulated in each voxel was multiplied by the ratio of the smeared energy to the original one. Both the size of the voxels and the energy resolution are extrapolations from results of the NEXT-DEMO prototype [13,15].…”

Application and performance of an ML-EM algorithm in NEXT

“…The NEXT detector concept provides excellent energy resolution, close to 0.5% at the Q value of 136 Xe [5,6]. The unique trace left in the detector by the decay makes track reconstruction an additional powerful handle to reject background [7].…”

Next

“…The energy resolution was measured with both detectors. In NEXT-DEMO, the 0.511 MeV 22 Na photopeak was reconstructed at 1.62% FWHM [2], while a resolution of 1.00% FWHM was achieved for the 0.662 MeV 137 Cs peak [3] in NEXT-DBDM (see Fig. 2).…”