In the fall, DLNP JINR scientists returned to the Gran Sasso National Laboratory (Italy) to continue the installation of enriched Ge-76 detectors in the LEGEND experiment. The preparatory work necessary for a full-scale launch of the experiment was carried out. This was followed by reassembly of the liquid argon instrumentation and all currently available detectors made from Ge-76. All operations were performed with the direct participation of our specialists.
The LEGEND experiment was launched this summer with four strings of germanium detectors (~ 60 kg) to assess the performance of all its elements: detectors, liquid argon instrumentation, electronics, DAQ and analysis stream. The test result satisfied the collaboration, and in October it was decided to stop the data taking. The setup was disassembled to prepare the full-scale LEGEND launch (adding missing cables, mounting all detector electronics, repairing broken channels, etc.). The JINR scientists took an active part in all stages of the work. Their role was often decisive. For example, our young scientist Nadezhda Rumyantseva in addition to tasks related to mounting detectors in holders and strings was responsible for the repair of failed light collection channels in the argon instrumentation, namely SiPM arrays.
After the successful completion of preparatory works, we fully reassembled the setup with a much larger number of detectors. During the week, a joint group of scientists carried out the following tasks:
- mounting the inner part of the liquid argon instrumentation;
- assembling 10 enriched germanium detector strings;
- putting the nylon mini-shrouds, made by JINR specialists, on the strings;
- mounting the outer part of the liquid argon instrumentation;
As a result, 101 germanium detectors have been installed in the experiment. The mass of the enriched isotope Ge-76 is about 140 kg. It exceeded 100 kg for the first time ever! For comparison, in the final phase of the previous GERDA experiment, which set the best limit for the half-life of the neutrinoless double beta decay of 1026 years, only 41 detectors with a total mass of ~40 kg were measured. In another germanium project, MAJORANA, the total mass was about 30 kg. The LEGEND experiment uses detectors from GERDA (BEGe type) and MAJORANA (PPC type). In both cases, the detector mass does not exceed 1 kg. In LEGEND-200 a noticeable increase of the enriched isotope has been achieved by using innovative detectors of the ICPC type which weigh up to 4 kg and on average over 2 kg. In the second phase of the experiment, LEGEND-1000, it is planned to immerse only ICPC detectors.
Next year, when the remaining detectors are made, they will be added to the setup to reach the target Ge-76 mass of 200 kg. Then, after 5 years of data taking, it is planned to accomplish the desired LEGEND-200 neutrinoless double beta decay sensitivity of 1027 years.
Konstantin Gusev, Nadezda Rumyantseva, Egor Shevchik, Daniya Zinatulina
— all DLNP JINR