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CROSS and CUPID-Mo : future strategies and new results in bolometric search for 0νββ

Abstract : Neutrinoless double-beta decay is a hypothetical rare nuclear transition (T₁/₂>10²⁶ yr). Its observation would provide an important insight about the nature of neutrinos ascertaining that they are Majorana particles and demonstrating that the lepton number is not conserved. This decay can be investigated with bolometers embedding the double beta decay isotope, the possibility to investigate this rare process is strongly influenced by the background level in the region of interest. A new R&D has recently begun within the CROSS project (Cryogenic Rare-event Observatory with Surface Sensitivity) aiming at the development of bolometric detectors, embedding the promising isotopes ¹⁰⁰Mo and ¹³⁰Te, capable of discriminating surface α et β interactions by exploiting the properties of superconducting material (Al film) or normal metal (Pd film) deposited on the crystal faces (Li₂MoO₄ and TeO₂). These films work as pulse-shape modifiers. The results of the tests on prototypes performed at CSNSM (Orsay, France) showed the capability of a few- μm (nm)-thick Al (Pd) film deposited on the crystal surface to discriminate surface from bulk events, with the required rejection level of the surface background. While Al film can only identify surface α particles, with normal-metal films we were able to separate also the β surface component. This is a breakthrough in bolometric technology for double beta decay that could lead to reach a background index in the range 10⁻⁵ counts/(keV kg yr). In addition, the thesis covers the CUPID-Mo experiment, a demonstrator of CUPID, the next-generation ton-scale cryogenic 0νββ experiment. CUPID-Mo employs Li₂MoO₄ scintillating bolometers that allows to discriminate between α and β/γ, thus rejecting the dominant contribution on the background that consists in α particle interactions. The experiment achieved a new limit on the half-life of 0νββ decay in ¹⁰⁰Mo of T₁/₂> 1.5 x 10²⁴ yr at 90% C.I., the best ever obtained worldwide on this isotope.
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Submitted on : Saturday, March 13, 2021 - 4:57:11 PM
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Hawraa Khalife. CROSS and CUPID-Mo : future strategies and new results in bolometric search for 0νββ. Instrumentation and Detectors [physics.ins-det]. Université Paris-Saclay, 2021. English. ⟨NNT : 2021UPASP002⟩. ⟨tel-03168547⟩

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