On 21 January, a joint meeting of the Programme Advisory Committees for Particle Physics and Nuclear Physics took place as a video conference. The event focused on the discussion of JINR projects in the fields of neutrino physics. JINR Director G. V. Trubnikov opened the event. The agenda of the meeting included reports on the projects of the topic “Non-accelerator neutrino physics and astrophysics” and proposals for their extension.

Following the principles proposed by JINR Director G. V. Trubnikov, the final aim of the Committees’ experts was to classify projects into three categories using the scheme adopted at the previous joint meeting in January 2019. The classification is based, first of all, on the scientific significance of a project, efficiency, and results of JINR teams. Information about the presented projects and Committees’ recommendations is provided below.

The PACs heard a report by K. N. Gusev on the GERDA (LEGEND) project focused on the search for neutrinoless double beta decay of ⁷⁶Ge using open Ge detectors immersed in liquid argon. The GERDA project is being implemented in Gran Sasso (Italy) by efforts of a large international community. The planned exposure of 100 kg per year reached, the second phase of the GERDA experiment (2015-2020) successfully started.

Impressive characteristics of GERDA gives confidence in the feasibility of the next-generation experiment LEGEND with a ton of ⁷⁶Ge. It is assumed that LEGEND will have two stages, just like GERDA. Up to 200 kg of germanium detectors will be used during the first stage inside the existing cryostat of GERDA. It is planned to reach a sensitivity of 10²⁷ years. This will require an improvement in the current background by 5 times. The full-scale project with 1 ton of ⁷⁶Ge aims at a sensitivity of 10²⁸ years by reducing the background by 10 times. The potential goal of the project is to determine the neutrino mass hierarchy.

The PACs recognized the important role the JINR group plays in the GERDA (LEGEND) experiments and recommended to continue the project in 2022-2024 with an A rating.

V. I. Tretyak reported on the SuperNEMO project focused on the search for neutrinoless double beta decay with the use of tracker-calorimeter methods that allow reconstructing angles and energies of decay products for each event. Many-year participation of DLNP JINR in experiments of the first-generation NEMO-2/3 led to the world-level results.

A new generation detector is being developed together with SuperNEMO in LSM (Modane). The JINR group plays a significant role in this project, in particular, in the creation of passive protection, the VETO system, a calorimeter, software, and data processing, as well as in the development of methods for radiochemical purification. The PACs noted that despite all these achievements, the implementation of the project is delayed for several years. Nevertheless, opportunities of the track calorimeter, as well as free selectivity for any of the candidate isotopes, would help SuperNEMO make its contribution to the assessment of a possible signal of the neutrinoless double beta decay discovered in other searches. The PACs recognized the potential of the method used by SuperNEMO and recommended to continue the project in 2022-2024 with a B rating. The PACs encourage authors to establish an effective group aimed to use the Demonstrator detector.

Yu. A. Shitov presented the DANSS reactor neutrino project at the Kalinin Nuclear Power Station. The project’s goal is to search for sterile neutrinos. A compact neutrino spectrometer of the DANSS project is safely installed next to the reactor. For five years of operation in 2016-2020, a world-record statistics of 4 million reactor antineutrinos was recorded (1 million events per year, or 5,000 events per day). This allowed DANSS to acquire world-level results.

The main task of the next stage of the project will be to modernize the DANSS-2 spectrometer to double the energy resolution. Thus, it will be possible to significantly expand the studied region of the phase space to search for sterile neutrinos. Furthermore, it is planned to continue the creation of the S-3 mini-spectrometer (S-cube) with a volume of about 64 litres with improved detecting elements. Such a detector will register 300-400 neutrinos per day and jointly with DANSS-2 will help better study the systematics of the measurement method used.

Compared to other neutrino experiments, the peculiarity of DANSS is that it operates near a powerful nuclear reactor and provides data of high scientific value with unprecedented statistics. The PACs recommended continuing the DANSS project in 2022-2024 with an A rating.

A. V. Lubashevsky proposed to prolong the vGeN (GEMMA) project, which is currently being implemented by a JINR group at the Kalinin Nuclear Power Station. The measurements focus on studying such properties of reactor neutrinos as the search for the magnetic neutrino moment and the coherent elastic neutrino scattering on the nucleus, i.e. the process that has been first identified using accelerator neutrinos.

The PAC highly evaluated responsibilities of the JINR group and its ability to independently carry out studies, as well as the potential of the project in the conditions of strong international rivalry, in particular, in observation of coherent neutrino scattering. It is recommended to continue and to provide full funding of the vGeN project in 2022-2024 with a B rating.

E. A. Yakushev devoted his report to the latest results of the EDELWEISS experiment and the continuation of its research programme with new HPGe cryogenic detectors-bolometers. The programme will be expanded by including studies on coherent elastic neutrino-nucleus scattering. The PACs noted the successful development of bolometric detectors, which allow conducting high-precision spectrometric measurements up to very low energies (with an energy threshold below 100 eV) under which the manifestation of new physics in the electroweak sector is expected in a form of the energy spectrum of recoil nuclei caused by CEvNS.

The first stage of the RICOCHET programme with a large-scale experiment will be carried out at the ILL research reactor (Grenoble, France). At the same time, EDELWEISS scientists will continue to use the advanced detectors for the direct search for particles of dark matter from the galactic halo in the fields of low-mass weakly interacting particles (1 GeV/c² and below). This field is not yet available for large-scale experiments with the use of detectors on liquefied noble gases. The PACs noted with satisfaction that the EDELWEISS-RICOCHET project aims at the solution of intriguing problems of modern physics, has achieved the world best results, and maintains strong competitive positions. It is recommended to expand the EDELWEISS research programme for the direct search of dark matter particles up to the RICOCHET project on the precision CEvNS measurement in 2022-2024 with an A rating.

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