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cupid_pub:the_cupid_experiment [2021/05/18 09:09] – [The 0υ2β decay] dilorenzo1 | cupid_pub:the_cupid_experiment [2021/06/01 08:23] – [The Experiment] dilorenzo1 | ||
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- | ====== | + | ====== CUPID ====== |
- | The project CUPID (CUORE Upgrade with Particle | + | The project |
- | ====== Physics Goal ====== | + | ===== Physics Goal ===== |
- | Neutrino particles | + | |
- | Despite neutrinos | + | Neutrinos |
- | Neutrino | + | Over the past decades, neutrinos |
+ | Nevertheless, | ||
+ | unambiguously indicates the existence of new physics beyond the Standard Model. | ||
+ | In parallel, several open questions tantalize the physics community since decades: | ||
+ | * What are the fundamental symmetries | ||
+ | * What is the origin of the asymmetry between the amount of Matter and that of Anti-Matter in the Universe? | ||
+ | * Why is the mass of neutrinos much smaller than that of the other leptons? | ||
+ | A possible answer to these questions | ||
- | If neutrinos are Majorana particles | + | 0νββ decay is a process in which a nucleus |
+ | without any counterbalancing emission of antiparticles. Since the introduction of the Fermi theory of β decay, | ||
+ | this would be the first example of a process that does not conserve | ||
+ | the difference between the number of particles and antiparticles. | ||
+ | In the framework of the Standard Model, 0νββ decay is a process that violates the lepton number L, | ||
+ | and, more fundamentally, | ||
+ | Hence, the observation of 0νββ decay would simultaneously prove that the conservation of B-L is only approximate | ||
+ | and that the Standard Model is thus just an approximate version of a broader theory, | ||
+ | and provide an unequivocal evidence for the existence of matter creating processes. | ||
+ | 0νββ is only possible if neutrinos | ||
+ | the mass of the three known (light) left-handed neutrinos could be generated by some heavy right-handed partner | ||
+ | via the so-called see-saw mechanism, which naturally accounts for the smallness of neutrino masses | ||
+ | in comparison to the Higgs-generated masses of all other known particles. | ||
+ | ===== The 0νββ decay signature ===== | ||
- | =====The | + | 0νββ decay is a 3 body decay, |
- | The measurement of the neutrinoless double beta decay (see figure below, the bottom part of the figure shows the 0υ2β) | + | and the two emitted electrons. Given its much larger mass, the daughter nucleus is subject |
- | + | Moreover, for most detector technologies the two emitted electrons are not distinguishable, | |
- | + | so only their sum energy is measurable. | |
- | {{ : | + | The experimental signature of 0νββ |
- | + | corresponding to the mass difference between | |
- | in addition to probe the Majorana nature of the neutrino, would give hints to explain the neutrino tiny mass with respect of the charged leptons mass and it would be the first evidence for lepton number violation. | + | |
- | + | ||
- | + | ||
- | The experimental signature of such decay is the presence of a mono-energetic peak at the Q-value of the reaction, | + | |
- | + | ||
- | + | ||
- | {{ : | + | |
+ | On the other hand, 2νββ decay is a 5 body decay, with again a negligible nuclear recoil. | ||
+ | In this case, the two antineutrinos escape undetected, so only a fraction of the Q-value | ||
+ | is shared between the electrons. The signature in this case is therefore a continuum from zero | ||
+ | to the Q-value. | ||
+ | |{{ cupid_pub: | ||
+ | |Decay scheme of 2νββ (top) and 0νββ decay (bottom). The two processes share the same parent and daughter nucleus, but differ for the number of emitted particles, and consequently their energy.|The measurable sum electron spectrum is a continuum for 2νββ decay, and an excess at Q< | ||
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=====The Experiment===== | =====The Experiment===== | ||
- | The first experiments trying to measure | ||
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- | Among the operating | ||
- | CUORE is located at the Laboratori Nazionali del Gran Sasso (LNGS) in the Abruzzo region, beneath Monte Aquila, surrounded by at least 1400 meters (~3800 m.w.e.) of rock in all the direction. | ||
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- | The CUORE detector is composed by 988 crystals operated at cryogenic temperature equipped with sensitive thermometers (bolometers) made by TeO< | ||
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- | The future of the CUORE experiment is the CUPID project, with the goal to measure the 0υ2β decay using 1500 | ||
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- | The CUPID crystal will be placed inside | ||
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- | ==== The Detector ==== | ||
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- | The CUPID crystals are operated as cryogenic calorimeters, | ||
- | {{ : | ||
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+ | The first experimental attempts to detect 0νββ decay are date back to the 1940s. Over the decades, many different technologies have been developed to search for this process on a variety of candidate isotopes. | ||
+ | Presently, [[https:// | ||
+ | It is located at the [[https:// | ||
+ | CUORE is composed of 988 TeO< | ||
+ | The CUORE detectors are operated in the largest dilution refrigerator ever build((J. Ouellet, [[https:// | ||
+ | |{{cupid_pub: | ||
+ | |The Gran Sasso National Park, below which the underground lab of LNGS is located.|The CUORE detectors right after their installation in the cryostat.| | ||
+ | CUPID will profit of the established CUORE cryogenic infrastructure, | ||
+ | Thus, CUPID will not only change the crystal, but also the candidate isotope. The reason for this choice is twofold: | ||
+ | on the one hand, Li< | ||
+ | on the other hand the candidate isotope < | ||
+ | (compared to 2527 keV of < | ||
+ | |{{cupid_pub: | ||
+ | |The CUORE/CUPID cryostat during its construction, | ||
+ | ===== The Detector ===== | ||
+ | In CUPID, the Li< | ||
+ | A particle interaction in the crystal produces phonons and scintillation light. | ||
+ | The heat from recombining phonons is read by a Neutron Transmutation Doped (NTD) germanium thermistor | ||
+ | glued to the crystal. The light escapes the crystal, inducing a phonon signal in the light detector, which is also read by an NTD. | ||
+ | |{{ cupid_pub: | ||
+ | |Schematic of a cryogenic calorimeter, |