LOBRES · Low background techniques on particle detectors for Rare Event Searches

Low background techniques on particle detectors for Rare Event Searches

The nature of Dark Matter (DM), which composes 27% of the Universe is one of the biggest open questions in modern physics. The most attractive DM candidates arise from extensions of the Standard Model (SM): axions and WIPMs. Weakly Interacting Massive Particles (WIMPs) appear in well-motivated extensions of the SM, like supersymmetry, and have been extensively searched over the last two decades. On the other hand, the axion arises from extensions of the SM as a solution to the strong-CP problem. Axions and WIMPs could have been produced in an early stage of the Universe and could separately explain the total amount of DM in the Universe. The use of Micromegas readouts has been recently introduced for axion and WIMPs searches and proposed for experiments like TREX-DM and IAXO. TREX-DM is located at the Canfranc Underground Laboratory (LSC) and looking for low-mass WIMPs (∼10 GeV), in a mass range that is currently attracting the interest of all mainstream experiments. IAXO is a new generation solar axion helioscope that aims to improve current sensitivities by more than one order of magnitude; the collaboration is currently building an intermediate version of the experiment, called BabyIAXO, with discovery potential. The low counting rates expected in these experiments require the experimental background to be reduced to the lowest possible level. Another important aspect to enhance the physics potential of IAXO and TREX-DM is the reduction of the low energy threshold, which would improve TREX-DM sensitivities to lower WIMP masses. It would also make IAXO sensitive to very low energy solar axions produced in axion-electron conversion processes. The objectives of the project are to reduce the background levels and to lower the energy threshold in IAXO and TREX-DM, with the aim of achieving sensitivity scenarios with discovery potential for axions and low-mass WIMPs. Different research lines have been developed to achieve these objectives: simulations to understand the different background contributions; the study of new Micromegas architectures, such as a Gas Electron Multiplier (GEM) pre-amplification stage and the development of different test-benches for the study of the background at surface level and in the LSC. The measurements carried out at the LSC showed record background levels of 10-7counts keV-1cm-2s-1. This level proves that the intrinsic background achievable with the Micromegas detectors meets the requirements for BabyIAXO. On the other hand, although a record surface level background of about 8.6 x10-7counts keV-1cm-2s-1 was also achieved, experimental data and simulations results indicate that new active shielding strategies are required to enable the tagging of cosmic-induced neutrons, which are considered to be the main contribution to the background at surface level. Finally, the development of a GEM preamplifier stage on top of the Micromegas readout planes showed excellent results with record thresholds down to 50 eV.

Data: CORDIS, © European Union