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Register a new userSensitivity of a tonne-scale NEXT detector for neutrinoless double beta decay searches
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Justo Mart\\'in-Albo
Publication date
2020
fields
Physics
and research's language is
English
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The Neutrino Experiment with a Xenon TPC (NEXT) searches for the neutrinoless double-beta decay of Xe-136 using high-pressure xenon gas TPCs with electroluminescent amplification. A scaled-up version of this technology with about 1 tonne of enriched xenon could reach in less than 5 years of operation a sensitivity to the half-life of neutrinoless double-beta decay decay better than 1E27 years, improving the current limits by at least one order of magnitude. This prediction is based on a well-understood background model dominated by radiogenic sources. The detector concept presented here represents a first step on a compelling path towards sensitivity to the parameter space defined by the inverted ordering of neutrino masses, and beyond.
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A high pressure xenon gas time projection chamber with electroluminescent amplification (EL HPGXe TPC) searching for the neutrinoless double beta ($0 ubetabeta$) decay offers: excellent energy resolution ($0.5-0.7%$ FWHM at the $Q_{betabeta}$), by amplifying the ionization signal with electroluminescent light, and tracking capabilities, as demonstrated by the NEXT collaboration using two kg-scale prototypes. The NEXT collaboration is building an EL HPGXe TPC capable of holding 100 kg (NEXT-100) of xenon isotopically enriched in ${{}^{136}rm Xe}$. The installation and commissioning of the NEXT-100 detector at the Laboratorio Subterraneo de Canfranc (LSC) is planned for 2018. The current estimated background level for the NEXT-100 detector is of $4times10^{-4}$ counts/keV-kg-yr or less in the energy region of interest. Assuming an energy resolution of 0.75$%$ FWHM at the $Q_{betabeta}$ and a $0 ubetabeta$ signal efficiency of about 28$%$, this gives an expected sensitivity (at 90$%$ CL) to the $0 ubetabeta$ decay half life of $T^{0 u}_{1/2}>6.0times10^{25}$ yr for an exposure of 275 kg yr. A first phase of the NEXT experiment, called NEW, is currently being commissioned at the LSC. The NEW detector is a scale 1:2 in size (1:10 in mass) of the NEXT-100 detector using the same materials and photosensors and will be used to perform a characterization of the $0 ubetabeta$ backgrounds and a measurement of the standard double beta decay with neutrinos (${2 ubetabeta}$). An 8 sigma significance for the ${2 ubetabeta}$ signal in the NEW detector has been estimated for a 100-day run.
NEXT-100 is an electroluminescent high-pressure xenon gas time projection chamber that will search for the neutrinoless double beta ($beta beta 0 u$) decay of Xe-136. The detector possesses two features of great value for $beta beta 0 u$ searches: energy resolution better than 1% FWHM at the $Q$ value of Xe-136 and track reconstruction for the discrimination of signal and background events. This combination results in excellent sensitivity, as discussed in this paper. Material-screening measurements and a detailed Monte Carlo detector simulation predict a background rate for NEXT-100 of at most $4times10^{-4}$ counts keV$^{-1}$ kg$^{-1}$ yr$^{-1}$. Accordingly, the detector will reach a sensitivity to the bbonu-decay half-life of $2.8times10^{25}$ years (90% CL) for an exposure of 100 $mathrm{kg}cdotmathrm{year}$, or $6.0times10^{25}$ years after a run of 3 effective years.
We propose a novel detection concept for neutrinoless double-beta decay searches. This concept is based on a Time Projection Chamber (TPC) filled with high-pressure gaseous xenon, and with separated-function capabilities for calorimetry and tracking. Thanks to its excellent energy resolution, together with its powerful background rejection provided by the distinct double-beta decay topological signature, the design discussed in this Letter Of Intent promises to be competitive and possibly out-perform existing proposals for next-generation neutrinoless double-beta decay experiments. We discuss the detection principles, design specifications, physics potential and R&D plans to construct a detector with 100 kg fiducial mass in the double-beta decay emitting isotope Xe(136), to be installed in the Canfranc Underground Laboratory.
We propose an EASY (Electroluminescent ApparatuS of high Yield) and SOFT (Separated Optimized FuncTion) time-projection chamber for the NEXT experiment, that will search for neutrinoless double beta decay (bb0nu) in Xe-136. Our experiment must be competitive with the new generation of bb0nu searches already in operation or in construction. This requires a detector with very good energy resolution (<1%), very low background con- tamination (1E-4 counts/(keV bullet kg bullet y)) and large target mass. In addition, it needs to be operational as soon as possible. The design described here optimizes energy resolution thanks to the use of proportional electroluminescent amplification (EL); it is compact, as the Xe gas is under high pressure; and it allows the measurement of the topological signature of the event to further reduce the background contamination. The SOFT design uses different sensors for tracking and calorimetry. We propose the use of SiPMs (MPPCs) coated with a suitable wavelength shifter for the tracking, and the use of radiopure photomultipliers for the measurement of the energy and the primary scintillation needed to estimate the t0. This design provides the best possible energy resolution compared with other NEXT designs based on avalanche gain devices. The baseline design is an Asymmetric Neutrino Gas EL apparatus (ANGEL), which was already outlined in the NEXT LOI. ANGEL is conceived to be easy to fabricate. It requires very little R&D and most of the proposed solutions have already been tested in the NEXT-1 prototypes. Therefore, the detector can be ready by 2013. In this Conceptual Design Report (CDR) we discuss first the physics case, present a full design of the detector, describe the NEXT-1 EL prototypes and their initial results, and outline a project to build a detector with 100 kg of enriched xenon to be installed in the Canfranc Underground Laboratory in 2013.
We present data characterizing the performance of the first segmented, N-type Ge detector, isotopically enriched to 85% $^{76}$Ge. This detector, based on the Ortec PT6x2 design and referred to as SEGA (Segmented, Enriched Germanium Assembly), was developed as a possible prototype for neutrinoless double beta-decay measurements by the {sc Majorana} collaboration. We present some of the general characteristics (including bias potential, efficiency, leakage current, and integral cross-talk) for this detector in its temporary cryostat. We also present an analysis of the resolution of the detector, and demonstrate that for all but two segments there is at least one channel that reaches the {sc Majorana} resolution goal below 4 keV FWHM at 2039 keV, and all channels are below 4.5 keV FWHM.
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