Simulations have been extensively used in this project, in which a background model has been developed to understand the effect of cosmic induced events. Simulation results show that the Micromegas background at surface level is limited by cosmic induced neutrons, while current active shielding strategies, which are based on plastic scintillators do not have capabilities to tag these neutrons. Therefore, these results were the starting point of a new research line for the development of new active shielding strategies with neutron tagging capabilities.
Different studies on novel Micromegas architectures were performed with the aim to improve the low energy threshold, including studies on segmented mesh Micromegas and the combination of a Micromegas with a GEM preamplifier stage. The GEM preamplifier stage showed promising results, with gain factors up to 100, while low energy thresholds of about 50 eV has been already achieved in the TREX-DM experiment, thus increasing TREX-DM sensitivity to low mass WIMPs.
Various test benches were developed with the aim of understanding the different contributions at surface level and at the LSC. The Micromegas operating at the LSC has been taking data using Xe and Ar-based mixtures and obtaining record background levels of 10-7counts keV-1cm-2s-1. The test-bench at surface level consist of a Micromegas detector fully covered by plastic scintillators as active muon veto, obtaining background levels of 8.6 x counts keV-1cm-2s-1. This background level is still far from BabyIAXO requirements, yet this value is the lowest background reached at surface level; simulations point out at cosmic-induced neutrons as the limiting factor of this background.
The project results have been disseminated in 4 publications (two more are in preparation); the results of the project and the methodology have been presented in the TAUP2023 international conference. The know-how on low background techniques has been disseminated during several IAXO Collaboration Meetings. For the general public, an article in a scientific inlet of a large circulation newspaper was published, while dedicated outreach talks and activities during the European Researcher’s Night for a broader audience have also been given. On the other hand, the project results are being exploited in the new research lines which have arisen from this project, such as the development of new active shielding strategies. In addition, the excellent results obtained in the reduction of the low energy threshold using a GEM preamplification stage can open new avenues and research lines. Besides, low WIMP mass searches, low energy threshold detectors are essential in other fields, such as reactor neutrino-nucleus scattering experiments.
