Contributed Review: The saga of neutrinoless double beta decay search with TeO2 thermal detectors

Abstract

Neutrinoless double beta decay (0νββ) is a direct probe of physics beyond the Standard Model. Its discovery would demonstrate that the lepton number is not a symmetry of nature and would provide us with unique information on the nature and mass of the neutrinos. Among the experimental techniques employed in the investigation of this rare process, thermal detectors fulfill the requirements for a powerful search, showing an excellent energy resolution and the possibility of scaling to very large masses. In this work, we review the long chain of bolometric experiments based on TeO 2 crystals that were and continue to be carried out at the Laboratori Nazionali del Gran Sasso (Italy), searching for the 0νββ of 130 Te. We illustrate the progress and improvements achieved in almost thirty years of measurements and compare the various performance and results. We describe the several steps that led to the CUORE detector, the latest of this series and presently in data taking, and we highlight the challenges that a next bolometric experiment will face in order to further improve the sensitivity, especially concerning the background abatement. Finally, we emphasize the advantages of 130 Te in the search for 0νββ with a further future experiment.Published on: Rev. Sci. Instrum. 89, 121502 (2018) CONTENTS

Charge-to-heat transducers exploiting the Neganov-Trofimov-Luke effect for light detection in rare-event searches

“…In neutrinoless double-beta searches based on heat-and-light composite bolometers, low threshold light detectors are used to suppress the background. In the case of TeO 2 based neutrinoless double-beta decay search, no exploitable scintillation signal is to-date available to reject the alpha (dominant) background in the region of interest [17]. However, a particle identification can be performed via Cherenkov radiation, emitted by electrons 3 [16].…”

“…In dark-matter searches, a high-performance light detector is required to lower the energy threshold [14] and to identify recoils of different-mass nuclei [15]. In double-beta decay searches, high-sensitivity light detectors are needed either to detect the feeble Cherenkov light emitted by poorlyscintillating crystals [16] (this is the case of the promising compound TeO 2 [17,18,19,20,21]), or to help in pile-up rejection (as in 100 Mo-enriched bolometers, [22,23,24]). The pile-up rejection capability is useful also to perform precision calorimetric measurements of rare-β-decay spectral shapes (as those of 113 Cd and 115 In) which can be used to scrutinize the value of the axialvector coupling constant [25,26,27].…”

Cosmogenic Activation in Double Beta Decay Experiments

“…The DBD of 130 Te has been largely studied using bolometers [115][116][117]. Thanks to a high natural isotopic abundance of 34%, enrichment is not necessary which makes it feasible to accumulate large amounts of tellurium oxide.…”

“…Two-neutrino DBD to excited states have been observed for both 100 Mo [195] and 150 Nd [196]. Other DBD emitters like 116 Cd can be studied using low background scintillators [197]. Even if limited in some cases, there is also information on the cosmogenic activation of targets containing some of these DBD isotopes.…”

“…The decay conserves the lepton number and is detectable for nuclei having an even number of neutrons and protons and the beta transition energetically forbidden or strongly suppressed by the angular momentum change. The DBD with emission of neutrinos, specifically reviewed in [15], has been observed for several nuclei ( 48 Ca, 76 Ge, 82 Se, 96 Zr, 100 Mo, 116 Cd, 128 Te, 130 Te, 136 Xe, 150 Nd and 238 U) with measured half-lives varying approximately from 10 19 to 10 24 y (see recommended values at [16]).…”