Neutrinos, in spite of their very small mass, have become more and more bulky in the field of the fundamental physics. In particular, understanding if neutrinos are “Majorana" or "Dirac" or particles (i.e. if they correspond or not to their own antiparticle) is a crucial step to have a clearer picture of our Universe. The only way to reveal this neutrino’s property is to look for the so-called neutrinoless double beta decay, a very rare nuclear transformation forbidden in the actual standard model of particle physics.
The idea of CUPID is to combine the standard bolometric technique with the simultaneous detection of the light emitted by an event in the bolometer itself. In this way, in addition to the very good energy resolution proper of the bolometric technique, the measurement of the emitted light allows for particle discrimination, providing an important tool to reduce the natural-induced radioactivity.
The scientific goal of CUPID is not just to look for the double beta decay, but also to lay the basis for a next-generation experiment that takes full advantage of the innovative potential of this new technique.
The project CUPID (CUORE Upgrade with Particle Identification) borns with the aim to build a bolometric experiment, able to operate in the zero-background conditions, using the CUORE infrastructure. The scientific goal is to explore the inverted hierarchy of neutrino masses, searching for the violation of the lepton number and the Majorana neutrino. The experience and skills gained through the many years of scientific research and technological development for the CUORE experiment will be used to test the maturity of the bolometer technology for a next-generation experiment.
A bolometer consists of a crystal coupled with a very sensitive thermometer: when a crystal is cooled, i.e. its absolute temperature is around 0.01 Kelvin degrees, very close to absolute zero (-273.14 degrees Celsius), a minimum and invisible energy release in it, produces a temperature variation. By measuring this variation we are able to reconstruct the energy released.
The first phase of CUPID is the construction of CUPID-0, the first experiment for the double beta decay search made with scintillating bolometers, able to achieve a sensitivity comparable to the current experiments. CUPID-0 will use the enriched Zn82Se crystals developed within the LUCIFER project. The single detector of CUPID-0 is as bolometer. In these crystals the release of energy, together with heat signals, causes a minimum production of light, that escapes from the crystal and can be measured. This feature is a fundamental tool to reduce the natural background radiation since α particles, that "mimics" the expected signal, have a different light yield with respect to the β/γ particles with the same energy. However at the cryogenic temperature required by the bolometers the “standard" light detectors do not work, so dedicated light detectors have to be used. They consist in very sensitive "opaque" bolometers, developed as part of the LUCIFER project since 2006, made of a 45 mm diameter and 0.1 mm thick slabs of Germanium. In fact the small amount of light emitted by ZnSe crystals (few hundreds photons) is enough to heat up the bolometric light detector and the temperature raise directly returns the number of the absorbed photons.
The CUPID-0 experiment is an array of individual detectors arranged in five towers (see Fig.1).
Figure 1: a) Lateral view of a single module: the ZnSe is placed between two light detectors (Ge-LD), not visible in this scheme because of their small thickness (about 170 μm); all the detectors are held in the copper structure using PTFE elements. Top (b) and 3D (c) views of the CUPID-0 detector. d) 3D view of the CUPID-0 detector hosted in the CUORE-0 cryostat.
The single module is constituted by a cylindrical crystal of diameter 45 mm and height 55 mm Zn82Se coupled with a bolometric Germanium light detectors.
The production of enriched Zn82Se crystals ended in February 2016, and the assembly of the detectors was completed in October 2016; then the detector array was installed in the same dilution cryostat dilution which housed the CUORE-0 experiment, cooled down at 0.01 K and the data taking is scheduled to start in early 2017.
As a part of the CUPID project, other enriched crystals are also tested, such as 130TeO2 and Li2100MoO4, with the idea of creating a second demonstrator in 2017/2018. Being the Li2100MoO4, also a scintillating crystal, a set-up very similar to CUPID-0 can be used; on the contrary the TeO2 is not a scintillating crystal, but it is possible to detect the Cherenkov light produced by the traveling electrons in the crystal to discriminate the α particles. However, the Cherenkov light emitted by the double beta decay is very tiny and requires the development of a more sensitive cryogenic light detector to be detected.
D. R. Artusa1,2, A. Balzoni3,4, J. W. Beeman5, F. Bellini3,4, M. Biassoni6, C. Brofferio6,7, A. Camacho8, S. Capelli6,7, L. Cardani4, P. Carniti6,7, N. Casali3,4, L. Cassina6,7, M. Clemenza6,7, O. Cremonesi7, A. Cruciani3,4, A. D'Addabbo1, I. Dafinei4, S. Di Domizio9,10, M. L. Di Vacri1, F. Ferroni3,4, L. Gironi6,7, A. Giuliani11, C. Gotti6,7, G. Keppel8, M. Maino6,7, M. Mancuso11,12,13, M. Martinez3,4, S. Morganti3, S. Nagorny15,1, M. Nastasi6,7, S. Nisi1, C. Nones12, F. Orio4, D. Orlandi1, L. Pagnanini14,1, M. Pallavicini9,10, V. Palmieri8, L. Pattavina1, M. Pavan6,7, G. Pessina7, V. Pettinacci3,4, S. Pirro1, S. Pozzi6,7, E. Previtali7, A. Puiu6,7, C. Rusconi2, K. Schäffner14,1, C. Tomei3, M. Vignati3, A. Zolotarova12.
1INFN, Laboratori Nazionali del Gran Sasso, Assergi, Italy
2Department of Physics and Astronomy, University of South Carolina, Columbia, USA
3Dipartimento di Fisica, Sapienza Università di Roma, Italy
4INFN, Sezione di Roma, Italy
5Material Science Division, Lawrence Berkeley National Laboratory, Berkeley, USA
6Dipartimento di Fisica, Università di Milano Bicocca, Milano, Italy
7INFN, Sezione di Milano Bicocca, Milano, Italy
8INFN, Laboratori Nazionali di Legnaro, Legnaro (Padova), Italy
9Dipartimento di Fisica, Università di Genova, Italy
10INFN, Sezione di Genova, Genova, Italy
11Centre de Spectrométrie Nucléaire et de Spectrométrie de Masse, Orsay, France
12CEA, Irfu, SPP Centre de Saclay, Gif-sur-Yvette, France
13Max Planck Institute fuer Physik, Munich, Germany
14Gran Sasso Science Institute, L’Aquila, Italy
Enriched TeO2 bolometers with active particle discrimination: towards the CUPID experiment
D.R. Artusa, F.T. Avignone, III, J.W. Beeman, I. Dafinei, L. Dumoulin, Z. Ge, A. Giuliani, C. Gotti, P. de Marcillac, S. Marnieros, S. Nagorny, S. Nisi, C. Nones , E.B. Norman, V. Novati, E. Olivieri , D. Orlandi, L. Pagnanini, L. Pattavina, G. Pessina, S. Pirro, D.V. Poda, C. Rusconi, K. Schäffner, N.D. Scielzo, Y. Zhu
Phys.Lett. B767 (2017) 321-329
First array of enriched Zn82Se bolometers to search for double beta decay
D. R. Artusa, A. Balzoni, J. W. Beeman, F. Bellini, M. Biassoni, C. Brofferio, A. Camacho, S. Capelli, L. Cardani, P. Carniti, N. Casali, L. Cassina, M. Clemenza, O. Cremonesi, A. Cruciani, A. D’Addabbo, I. Dafinei, S. Di Domizio, M. L. di Vacri, F. Ferroni, L. Gironi, A. Giuliani, C. Gotti, G. Keppel, M. Maino, M. Mancuso, M. Martinez, S. Morgante, S. Nagorny, M. Nastasi, S. Nisi, C. Nones, F. Orio, D. Orlandi, L. Pagnanini, M. Pallavicini, V. Palmieri, L. Pattavina, M. Pavan, G. Pessina, V. Pettinacci, S. Pirro, S. Pozzi, E. Previtali, A. Puiu, C. Rusconi, K. Schäffner, C. Tomei, M. Vignati, A. Zolotarova
Eur. Phys. J. C76 (2016) no.7, 364
Double-beta decay investigation with highly pure enriched Se for the LUCIFER experiment
J. W. Beeman, F. Bellini, P. Benetti, L. Cardani, N. Casali, D. Chiesa, M. Clemenza, I. Dafinei, S. Di Domizio, F. Ferroni, L. Gironi, A. Giuliani, C. Gotti, M. Laubenstein, M. Maino, S. Nagorny, S. Nisi, C. Nones, F. Orio, L. Pagnanini, L. Pattavina, G. Pessina, G. Piperno, S. Pirro, E. Previtali, C. Rusconi, K. Schffner, C. Tomei, M. Vignati
Eur.Phys.J. C75 (2015) no.12, 591
Current Status and Future Perspectives of the LUCIFER Experiment
J. W. Beeman, F. Bellini, P. Benetti, L. Cardani, N. Casali, D. Chiesa, M. Clemenza, I. Dafinei, S. Di Domizio, F. Ferroni, A. Giachero, L. Gironi, A. Giuliani, C. Gotti, M. Maino, S. Nagorny, S. Nisi, C. Nones, F. Orio, L. Pattavina, G. Pessina, G. Piperno, S. Pirro, E. Previtali, C. Rusconi, M. Tenconi, C. Tomei, M. Vignati
Advances in High Energy Physics Volume 2013
CUPID: CUORE (Cryogenic Underground Observatory for Rare Events) Upgrade with Particle Identification
R&D towards CUPID (CUORE Upgrade with Particle Identification)