Periodic Reporting for period 2 - BINGO (Bi-Isotope 0n2b Next Generation Observatory)
Reporting period: 2022-04-01 to 2023-09-30
BINGO is actively developing a novel suite of technologies aimed at enabling neutrino physicists to conduct a future experiment with wide sensitivity across the parameter space of neutrino mass. Specifically, the experiment seeks to explore the possibility of neutrinos being of the Majorana type, which implies being identical to their antiparticles. By employing these cutting-edge technologies, BINGO-like future experiments aim to observe neutrinoless double beta decay, a long-standing hypothesized phenomenon that has yet to be detected. Such a discovery would not only confirm the Majorana nature of neutrino mass but also determine the neutrino mass scale by measuring a specific combination of the three mass eigenvalues. Furthermore, it may shed light on the intriguing disparity between the abundance of matter and the scarcity of antimatter in the Universe.
The question BINGO is addressing stands as one of the utmost priorities in modern neutrino physics, offering the potential to revolutionize our understanding of elementary particles. The possible detection of neutrinoless double beta decay would truly be transformative.
To achieve this significant breakthrough in double beta decay research, BINGO is devising groundbreaking and innovative solutions to effectively control background noise in bolometric technology. These solutions will be rigorously tested and validated through a two-isotope demonstrator named MINI-BINGO, situated in the Modane underground laboratory. Furthermore, there is a strong possibility that all of some of these advancements will be embraced by upcoming ton-scale searches such as CUPID-1T. It is important to note that this experiment is a continuation of the current bolometric searches, including CUORE, one of the most sensitive ongoing experiments currently collecting data in the Gran Sasso underground laboratory, and CUPID, its projected successor.
The question BINGO is addressing stands as one of the utmost priorities in modern neutrino physics, offering the potential to revolutionize our understanding of elementary particles. The possible detection of neutrinoless double beta decay would truly be transformative.
To achieve this significant breakthrough in double beta decay research, BINGO is devising groundbreaking and innovative solutions to effectively control background noise in bolometric technology. These solutions will be rigorously tested and validated through a two-isotope demonstrator named MINI-BINGO, situated in the Modane underground laboratory. Furthermore, there is a strong possibility that all of some of these advancements will be embraced by upcoming ton-scale searches such as CUPID-1T. It is important to note that this experiment is a continuation of the current bolometric searches, including CUORE, one of the most sensitive ongoing experiments currently collecting data in the Gran Sasso underground laboratory, and CUPID, its projected successor.
The BINGO detectors will be scintillating bolometers based on TeO2 and Li2MoO4 crystals, containing the double beta decay candidate isotopes Te-130 and Mo-100 respectively. These devices are operated close to the absolute zero and measure simultaneously the heat and the scintillation light developed by a nuclear event, allowing for particle identification and consequently background mitigation.
Twelve radiopure crystals of both types have been procured and are now available for the final BINGO demonstrator, named MINI-BINGO.
The millikelvin cryostat that will house MINI-BINGO in Modane has been designed and ordered. It will be commissioned in fall 2023.
A semi-automatic system to glue the temperature sensors to the crystals was designed and fabricated. It is currently under test.
The first technological innovation in BINGO is the development of a bolometric light detector improved by the Neganov-Luke effect, provided with the same readout used for the large crystals. We have already demonstrated that the BINGO objectives for these devices can be reached, over a set of ten identical detectors tested underground. Their design is preliminary and the performance of these devices will be further improved.
The second technological innovation represents a total change of philosophy in the way crystals are supported in macro-bolometers. The light detector – with a square cross-section – will shield completely the copper support. Out of the six cubic sides of the crystals, one will face the light detector and the remaining five the nearby crystals. Rejection of charged particles emitted by surface radioactivity will be very efficient through anticoincidence. To implement this configuration, a holding method for the large crystals was developed, involving the use of tensioned nylon wire (4- 5 kg tension). This configuration was successfully tested with above-ground prototypes and finally validated underground, with a module of four crystals.
The third technological innovation introduces – for the first time in a large array of macro-bolometers – an active inner shield capable to reduce dramatically the background contribution from the external gamma radioactivity. Scintillators of different materials have been tested for the construction of the active veto. The final choice has fallen on BGO. The barrel surrounding the detectors will comprise thirty-two BGO trapezoidal prisms, while the endcaps will consist of BGO cylindrical crystals. A prototype with two prisms has been tested above ground. The test was overall successful, even if it shows some challenging points that will be addressed with a slight modification of the design.
Twelve radiopure crystals of both types have been procured and are now available for the final BINGO demonstrator, named MINI-BINGO.
The millikelvin cryostat that will house MINI-BINGO in Modane has been designed and ordered. It will be commissioned in fall 2023.
A semi-automatic system to glue the temperature sensors to the crystals was designed and fabricated. It is currently under test.
The first technological innovation in BINGO is the development of a bolometric light detector improved by the Neganov-Luke effect, provided with the same readout used for the large crystals. We have already demonstrated that the BINGO objectives for these devices can be reached, over a set of ten identical detectors tested underground. Their design is preliminary and the performance of these devices will be further improved.
The second technological innovation represents a total change of philosophy in the way crystals are supported in macro-bolometers. The light detector – with a square cross-section – will shield completely the copper support. Out of the six cubic sides of the crystals, one will face the light detector and the remaining five the nearby crystals. Rejection of charged particles emitted by surface radioactivity will be very efficient through anticoincidence. To implement this configuration, a holding method for the large crystals was developed, involving the use of tensioned nylon wire (4- 5 kg tension). This configuration was successfully tested with above-ground prototypes and finally validated underground, with a module of four crystals.
The third technological innovation introduces – for the first time in a large array of macro-bolometers – an active inner shield capable to reduce dramatically the background contribution from the external gamma radioactivity. Scintillators of different materials have been tested for the construction of the active veto. The final choice has fallen on BGO. The barrel surrounding the detectors will comprise thirty-two BGO trapezoidal prisms, while the endcaps will consist of BGO cylindrical crystals. A prototype with two prisms has been tested above ground. The test was overall successful, even if it shows some challenging points that will be addressed with a slight modification of the design.
The impact of BINGO in the search for neutrinoless double beta decay will be at three levels: (i) validation of ground-breaking technologies for the control of the background in MINI-BINGO; (ii) application of one or more of these technologies to future experiments like CUPID and CUPID-1T, the proposed follow-ups to CUORE experiment in the Gran Sasso underground laboratory (LNGS); (iii) pave the way to large long-term experiments able to demonstrate the Majorana nature of neutrinos even in case of vanishing lightest neutrino mass and direct ordering of the three neutrino masses.