Background due to stored electrons following nuclear decays in the KATRIN spectrometers and its impact on the neutrino mass sensitivity

摘要

The KATRIN experiment is designed to measure the absolute neutrino mass scalewith a sensitivity of 200 meV at 90% C.L. by high resolution tritiumbeta-spectroscopy. A low background level of 10 mHz at the beta-decay endpointis required in order to achieve the design sensitivity. In this paper wediscuss a novel background source arising from magnetically trapped keVelectrons in electrostatic retarding spectrometers. The main sources of theseelectrons are alpha-decays of the radon isotopes (219,220)Rn as well asbeta-decays of tritium in the volume of the spectrometers. We characterize theexpected background signal by extensive MC simulations and investigate theimpact on the KATRIN neutrino mass sensitivity. From these results we refinedesign parameters for the spectrometer vacuum system and propose activebackground reduction methods to meet the stringent design limits for theoverall background rate.