Periodic Reporting for period 3 - CENNS (Probing new physics with Coherent Elastic Neutrino-Nucleus Scattering and a tabletop experiment)
Berichtszeitraum: 2022-02-01 bis 2023-07-31
Ever since the Higgs boson was discovered at the LHC in 2012, we had the confirmation that the Standard Model (SM) of particle physics has to be extended. In parallel, the long lasting Dark Matter (DM) problem, supported by a wealth of evidence ranging from precision cosmology to local astrophysical observations, has been suggesting that new particles should exist. Unfortunately, neither the LHC nor the DM dedicated experiments have significantly detected any exotic signals pointing toward a particular new physics extension of the SM so far.
With this research program, we want to take a new path in the quest of new physics searches by providing the first high-precision measurement of the neutral current Coherent Elastic Neutrino-Nucleus Scattering (CENNS). By focusing on the sub-100 eV CENNS induced nuclear recoils, the goal is to reach unprecedented sensitivities to various exotic physics scenarios with major implications from cosmology to particle physics, beyond the reach of existing particle physics experiments. These include for instance the existence of sterile neutrinos and of new mediators, that could be related to the DM problem, and the possibility of Non Standard Interactions that would have tremendous implications on the global neutrino physics program.
To this end, we are building a kg-scale cryogenic neutrino experiment with outstanding sensitivity to low-energy nuclear recoils, called CryoCube, that will be deployed at the ILL nuclear research reactor within the forthcoming Ricochet low-energy neutrino observatory. To provide the required new physics sensitivity, we need to push our detector technology beyond the state-of-the-art performance to reach sub-100 eV energy thresholds with unparalleled background rejection capabilities.
The CENNS research program is structured as follows:
WP1: Single crystal detector design
WP2: From a single crystal to a CryoCube detector array
WP3: Probing new physics with CENNS
With this research program, we want to take a new path in the quest of new physics searches by providing the first high-precision measurement of the neutral current Coherent Elastic Neutrino-Nucleus Scattering (CENNS). By focusing on the sub-100 eV CENNS induced nuclear recoils, the goal is to reach unprecedented sensitivities to various exotic physics scenarios with major implications from cosmology to particle physics, beyond the reach of existing particle physics experiments. These include for instance the existence of sterile neutrinos and of new mediators, that could be related to the DM problem, and the possibility of Non Standard Interactions that would have tremendous implications on the global neutrino physics program.
To this end, we are building a kg-scale cryogenic neutrino experiment with outstanding sensitivity to low-energy nuclear recoils, called CryoCube, that will be deployed at the ILL nuclear research reactor within the forthcoming Ricochet low-energy neutrino observatory. To provide the required new physics sensitivity, we need to push our detector technology beyond the state-of-the-art performance to reach sub-100 eV energy thresholds with unparalleled background rejection capabilities.
The CENNS research program is structured as follows:
WP1: Single crystal detector design
WP2: From a single crystal to a CryoCube detector array
WP3: Probing new physics with CENNS
During these four years, and according to the DoA, the team has focused on:
- Finalizing the installation of the clean room and more importantly get trained and highly experienced in building and mounting the detectors which were designed by the team. As of today, the ERC team has fabricated up to 20 bolometers, including the mechanical integration in our newly designed copper holders, NTD gluing (heat channel), electrode evaporation (ionization channel), and thermal/electrical bondings.
- The Ge technology has significantly progressed, the heat energy resolution using NTD (not NbSi as initially planned) has been achieved on these newly designed 38g bolometers (WP 1 – task 1). The electrodes, in two different and both promising designs, have been accomplished and have been tested extensively over the last two years. Both electrode designs have been validated (WP 1 – task 2).
- As mentioned in the previous report, despite of the interesting data we took with the Zn bolometers, it has been decided to first secure the Ge technology which is much more mature in order to be timely with the future Ricochet experiment installation and guarantee the science outcome from this project (WP3). Task 3 – WP1 will therefore be postponed to later times and not further considered within this ERC research program except if time allows. Therefore, with the completion of Task 1 and Task 2 from WP1, which will allow for the delivery a highly innovative and performing CryoCube detector array (WP2) with a proposal paper published in JLTP with first performance demonstration (10.1007/s10909-023-02960-8) we now consider WP1 completed.
- The CryoCube detector assembly is still being designed. Due to the late arrival of the Ricochet cryostat which could host the full CryoCube, we decided to divide the array in sub-arrays, dubbed Mini-CryoCube hosting three bolometers, that can be hosted in our current R&D cryostat in Lyon. We have been able to demonstrate that this MiniCryoCube design can handle both the 1K and 10 mK stages 5 centimeters apart with a minimal 1 uW heat load. Thanks to this successful demonstration we are finalizing the design of the full CryoCube array that will be composed of 6-to-9 MiniCryoCube added together. As such, task 1 – WP2 is almost completed as the major technological milestone and risk have been successfully overcome.
- A HEMT characterization bench has been developed to design, test, and validate our developed HEMT- preamplifier discussed from WP 2 – task 2. Following our amplifier design published in JLTP (10.1007/s10909-019-02269-5) and after one year of R&D on our HEMT-based preamplifiers prototypes, together with a MiniCryoCube array we have been able to achieve a world leading result in achieving a 30 eVee (RMS) ionization resolution on a 38g Ge bolometer operated at 15 mK. This is a major result of this ERC research program and a dedicated paper validating WP2 – task 1 and task 2 is to be published in EPJC (accepted with minor corrections - 10.48550/arXiv.2306.00166). Finally, with the recent first demonstration of the dual heat and ionisation readout with our newly developed MiniCryoCube detector technology (including its dedicated cold and warm electronics), with performance now around a factor of only two from the ERC goals, we now consider WP2 almost fully completed. It will be 100% completed mid-2024 when the full CryoCube array will be delivered, but no technological challenges are forseen anymore on the detector development program of this ERC.
- As already reported, but of tremendous importance, a significant amount of work has been done to secure the construction of the future Ricochet experiment by finding additional partners (10 institutions between USA, France and Russia), funding and resources, and a nuclear reactor site. The PI of this ERC-CENNS program has now become the spokesperson of this future experiment, based on an international collaboration of over 80 physicists, engineers and technicians. Ricochet is now secured and is currently being constructed at ILL. Also, the Ricochet cryostat has been commissioned and validated with CryoCube detector prototypes over 2022 and 2023 at Lyon, and is now being deployed at ILL. Though not directly related to this ERC program these progresses are pivotal to achieve the final science outcome of this ERC-CENNS research program by providing the required experimental infrastructure to host the CryoCube and deliver the first low-energy and high-precision measurement of the coherent neutrino process (WP3). Therefore, this parallel effort was absolutely essential to guarantee the full success of this ERC research program by ensuring the feasibility of the final scientific outcome. The first Ricochet @ ILL paper, detailing the design and specifications of the future Ricochet experiment, has been published in EPJC: 10.1140/epjc/s10052-022-11150-x.
- Finalizing the installation of the clean room and more importantly get trained and highly experienced in building and mounting the detectors which were designed by the team. As of today, the ERC team has fabricated up to 20 bolometers, including the mechanical integration in our newly designed copper holders, NTD gluing (heat channel), electrode evaporation (ionization channel), and thermal/electrical bondings.
- The Ge technology has significantly progressed, the heat energy resolution using NTD (not NbSi as initially planned) has been achieved on these newly designed 38g bolometers (WP 1 – task 1). The electrodes, in two different and both promising designs, have been accomplished and have been tested extensively over the last two years. Both electrode designs have been validated (WP 1 – task 2).
- As mentioned in the previous report, despite of the interesting data we took with the Zn bolometers, it has been decided to first secure the Ge technology which is much more mature in order to be timely with the future Ricochet experiment installation and guarantee the science outcome from this project (WP3). Task 3 – WP1 will therefore be postponed to later times and not further considered within this ERC research program except if time allows. Therefore, with the completion of Task 1 and Task 2 from WP1, which will allow for the delivery a highly innovative and performing CryoCube detector array (WP2) with a proposal paper published in JLTP with first performance demonstration (10.1007/s10909-023-02960-8) we now consider WP1 completed.
- The CryoCube detector assembly is still being designed. Due to the late arrival of the Ricochet cryostat which could host the full CryoCube, we decided to divide the array in sub-arrays, dubbed Mini-CryoCube hosting three bolometers, that can be hosted in our current R&D cryostat in Lyon. We have been able to demonstrate that this MiniCryoCube design can handle both the 1K and 10 mK stages 5 centimeters apart with a minimal 1 uW heat load. Thanks to this successful demonstration we are finalizing the design of the full CryoCube array that will be composed of 6-to-9 MiniCryoCube added together. As such, task 1 – WP2 is almost completed as the major technological milestone and risk have been successfully overcome.
- A HEMT characterization bench has been developed to design, test, and validate our developed HEMT- preamplifier discussed from WP 2 – task 2. Following our amplifier design published in JLTP (10.1007/s10909-019-02269-5) and after one year of R&D on our HEMT-based preamplifiers prototypes, together with a MiniCryoCube array we have been able to achieve a world leading result in achieving a 30 eVee (RMS) ionization resolution on a 38g Ge bolometer operated at 15 mK. This is a major result of this ERC research program and a dedicated paper validating WP2 – task 1 and task 2 is to be published in EPJC (accepted with minor corrections - 10.48550/arXiv.2306.00166). Finally, with the recent first demonstration of the dual heat and ionisation readout with our newly developed MiniCryoCube detector technology (including its dedicated cold and warm electronics), with performance now around a factor of only two from the ERC goals, we now consider WP2 almost fully completed. It will be 100% completed mid-2024 when the full CryoCube array will be delivered, but no technological challenges are forseen anymore on the detector development program of this ERC.
- As already reported, but of tremendous importance, a significant amount of work has been done to secure the construction of the future Ricochet experiment by finding additional partners (10 institutions between USA, France and Russia), funding and resources, and a nuclear reactor site. The PI of this ERC-CENNS program has now become the spokesperson of this future experiment, based on an international collaboration of over 80 physicists, engineers and technicians. Ricochet is now secured and is currently being constructed at ILL. Also, the Ricochet cryostat has been commissioned and validated with CryoCube detector prototypes over 2022 and 2023 at Lyon, and is now being deployed at ILL. Though not directly related to this ERC program these progresses are pivotal to achieve the final science outcome of this ERC-CENNS research program by providing the required experimental infrastructure to host the CryoCube and deliver the first low-energy and high-precision measurement of the coherent neutrino process (WP3). Therefore, this parallel effort was absolutely essential to guarantee the full success of this ERC research program by ensuring the feasibility of the final scientific outcome. The first Ricochet @ ILL paper, detailing the design and specifications of the future Ricochet experiment, has been published in EPJC: 10.1140/epjc/s10052-022-11150-x.
Based on our ongoing progress and research program, the next steps are results are:
- Deploy the Ricochet cryostat with the CryoCube at ILL to the commisioning of the experiment, including the CryoCube technology onsite.
- Deliver the full CryoCube payload by end-2024
- Scale up the electronics to readout the whole CryoCube detector array
- Deliver the first low-energy and high precision CENNS measurement to search for new physics in the electroweak sector by the end of ERC project (completion of WP3).
- Deploy the Ricochet cryostat with the CryoCube at ILL to the commisioning of the experiment, including the CryoCube technology onsite.
- Deliver the full CryoCube payload by end-2024
- Scale up the electronics to readout the whole CryoCube detector array
- Deliver the first low-energy and high precision CENNS measurement to search for new physics in the electroweak sector by the end of ERC project (completion of WP3).