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Towards the NEXT generation of bb0nu experimets

Final Report Summary - NEXT (Towards the NEXT generation of bb0nu experimets)

This project has developed a novel technology to search for neutrinoless double beta decay processes (NLDBD).
The discovery of NLDBD would be a major achievement in particle physics and cosmology, since it would demonstrate that the neutrino is its own antiparticle, providing also a potential mechanism to explain the cosmic asymmetry between matter and antimatter.
Discovery of NLDBD, on the other hand, depends on the effective mass of the neutrino (m■) which is known to be very small. Consequently, the lifetime of the process is very large, with experimental limits of the order of T~1026 years. The target of the next generation of NLDBD experiments is to improve such limit by an order of magnitude (T~1027 years). A discovery may require, ultimately, to improve the current sensitivity by two orders of magnitude (T~1028 years).
Sensitivity to such long lifetimes require that experiments deploy very large masses, of the order of several tons of isotopes, while at the same time achieving extremely low background levels (of the order of 1 event per ton and year in the region of interest or ROI for T~1027 y and 0.1 events for T~1028 y).
This project has developed the technology of high pressure xenon time projection chambers with electroluminescent TPC (HPXeEL). It has demonstrated that ton scale detectors can be built based in HPXeEL thanks to the combination of excellent energy resolution, a powerful topological signature (e.g. identification of the two electron emitte in the decay Xe-136 -> Ba-136 + 2e), and the additional demonstration that the single atom of Ba-136 can be tagged by the detector. The combination of this three conditions permits the construction of an essentially background free detector able to reach eventually sensitivities in the range of T~1028 y. The NEXT-White detector, fully financed by this project has allowed the demonstration of energy resolution and topological signature. The R&D carried out also in the context of this project has recently resulted in a landmark paper in Nature demonstrating the possibility of Barium Tagging in NEXT.

In addition two major spinoffs have resulted from the project. PETALO, a project to build a full-body PET based on Liquid Xenon (which has obtained an StG/ERC), and DÉTENTE, a project to detect SARS-COV-2 viruses based in the technology developed for SABAT.