Laboratorio Subterraneo De Canfranc Research Articles

Neutrinoless Double-Beta Decay Searches with Enriched $$^{116}\hbox {CdWO}_{{4}}$$ Scintillating Bolometers

Cadmium-116 is one of the favorable candidates for neutrinoless double-beta decay ($$0\nu \beta \beta $$) searches from both theoretical and experimental points of view, in particular thanks to the high energy of the decay (2813.49 keV), the possibility of the industrial enrichment in $$^{116}\mathrm{Cd}$$ and its use in the well-established production of cadmium tungstate crystal scintillators. In this work, we present low-temperature tests of two $$0.6\ \mathrm{kg} \ ^{116}\hbox {CdWO}_{{4}}$$ crystals enriched in $$^{116}\mathrm{Cd}$$ to $$82\%$$ as scintillating bolometers. These detectors were operated underground, with one at the Laboratoire Souterrain de Modane (LSM) in France and the second at the Laboratorio Subterraneo de Canfranc (LSC) in Spain. The two crystals are coupled to bolometric Ge light detectors in order to register the scintillation light. The double readout of heat and scintillation enables reduction in the background in the region of interest by discriminating between different populations of particles. The main goal of these tests is the study of the crystals’ radiopurity and the detectors’ performance. The achieved results are extremely promising, in particular, the detectors demonstrate a high energy resolution (11–16 keV FWHM at 2615 keV) and a high-efficiency discrimination of the alpha background ($$\sim 20 \sigma $$). These results, achieved for the first time with large mass enriched $$^{116}\hbox {CdWO}_{{4}}$$ crystals, demonstrate prospects of the bolometric technology for high-sensitivity searches of $$^{116}\mathrm{Cd}$$$$0\nu \beta \beta $$ decay.

The NEXT experiment for neutrinoless double beta decay searches

The goal of the NEXT experiment is the observation of the neutrinoless double beta decay in 136Xe using a gaseous xenon TPC with electroluminescent amplification and specialized photodetector arrays for calorimetry and tracking. After a prototyping period (2009-2014) where the technique was demonstrated, the Collaboration has completed the construction and started the operation of its first phase (NEXT-White or NEW) in the Laboratorio Subterraneo de Canfranc, in the Spanish Pyrenees, with the objectives of measuring in-situ the NEXT background model and the two-neutrino mode of the double beta decay under a radiopure regime. After running NEW, the Collaboration will operate a bigger detector, NEXT-100, which will look for the neutrinoless decay mode.

The NEXT high pressure xenon gas TPC for neutrinoless double beta decay searches

A high pressure xenon gas time projection chamber with electroluminescent amplification (EL HPGXe TPC) offers for the search of the neutrinoless double beta decay (0νββ): an excellent energy resolution (0.5−0.7% FWHM at the Qββ) and tracking capabilities as demonstrated by the NEXT collaboration using two kg-scale prototypes. The NEXT collaboration is constructing an EL HPGXe TPC capable to hold 100 kg (NEXT-100) of xenon isotopically enriched in 136Xe. Since October 2016, a first phase of the NEXT experiment, called NEW detector, is running with depleted 136Xe at the Laboratorio Subterraneo de Canfranc. The NEW detector is a scale 1:2 in size of the NEXT-100 detector and uses same materials and photosensors. It will be used to perform a characterization of the 0νββ backgrounds and a measurement of the standard double beta decay rate. Recent results on the characterization of the NEW detector performance using data from calibration sources are presented.

The NEXT double beta decay experiment

NEXT (Neutrino Experiment with a Xenon TPC) is a neutrinoless double-beta (ββ0v) decay experiment at Laboratorio Subterraneo de Canfranc (LSC). It is an electroluminescent Time Projection Chamber filled with high pressure 136Xe gas with separated function capabilities for calorimetry and tracking. Energy resolution and background suppression are the two key features of any neutrinoless double beta decay experiment. NEXT has both good energy resolution (< 1% FWHM) and an extra handle for background identification provided by track reconstruction. We expect a background rate of 4 × 10-4 counts keV-1 kg-1 yr-1, and a sensitivity to the Majorana neutrino mass of between 80-160 meV (depending on NME) after a run of 3 effective years of the 100 kg scale NEXT-100 detector. The initial phase of NEXT-100, called NEW, is currently being commissioned at LSC. It will validate the NEXT background rate expectations and will make first measurements of the two neutrino ββ2v mode of 136Xe. Furthermore, the NEXT technique can be extrapolated to the tonne scale, thus allowing the full exploration of the inverted hierarchy of neutrino masses. These proceedings review NEXT R&D results, the status of detector commissioning at LSC and the NEXT physics case.

Recent Performance of Scintillating Bolometers Developed for Dark Matter Searches

Scintillating bolometers of sapphire, BGO and LiF have been recently tested both at the Institut d’Astrophysique Spatiale (IAS) and the Laboratorio Subterraneo de Canfranc (LSC) in the frame of the ROSEBUD collaboration. We report on their response to different particles (α, β, γ and nuclear recoils) both in the heat and light channel. Signal output parameters for the different particles have been compared. We have focused on the study of the nuclear recoils discrimination against β/γ background events at low energy. The β/γ and nuclear recoil spectra obtained in the different runs are shown and analyzed. We also discuss the sensitivity of the LiF bolometer for measuring thermal neutron flux at LSC.