Micromegas readouts for double beta decay searches

Double beta (β β) decay experiments are one of the most active research topics in Neutrino Physics. The measurement of the neutrinoless mode 0 ν β β could give unique information on the neutrino mass scale and nature. The current generation of experiments aims at detector target masses at the 100 kg scale, while the next generation will need to go to the ton scale in order to completely explore the inverse hierarchy models of neutrino mass. Very good energy resolutions and ultra-low background levels are the two main experimental requirements for a successful experiment. The topological information of the β β events offered by gaseous detectors like gas Time Projection Chambers (TPC) could provide a very powerful tool of signal identification and background rejection. However only recent advances in TPC readouts may assure the competitiveness of a high pressure gas TPCs for β β searches, especially regarding the required energy resolution. In this paper we present first results on energy resolution with state-of-the-art micro-bulk Micro-mesh Gas Amplification Structure (Micromegas) using a 5.5 MeV alpha source in high pressure pure xenon. Resolutions down to 2 % FWHM have been achieved for pressures up to 5 bar. These results, together with their recently measured radio-purity, prove that Micromegas readouts are not only a viable option but a very competitive one for β β searches. (authors)