Title: Backgrounds at the KATRIN Neutrino Experiment


The KATRIN experiment is aiming to directly measure the ective electron anti neutrino mass from the kinematics of Tritium beta-decay. KATRIN is located at KIT (Karlsruhe Institute of Technology) and is currently under construction; it will prospec- tively start taking data in 2014. The experiment will analyze the shape of the high energy end of the tritium spectrum. A nonzero neutrino mass reduces the endpoint energy and distorts the spectrum, especially in the vicinity of this endpoint. This spectrum will be analyzed with a 24 m x 10 m electrostatic spectrometer combined with magnetic collimation (MAC-E- Filter). To reach the design sensitivity of 200 meV, high energy resolution, high signal count-rates and especially ultra low background of 10 mHz are required. Since KATRIN is not in an underground laboratory it is exposed to the cosmic muon flux. Hence, muon-induced electrons are an unavoidable background source. KATRIN provides both an electric and magnetic shielding system to keep such electrons from reaching the detector. A second background source is due to Penning traps, which typically occur close to complex electrode structures. Measurements show that even small Penning traps can lead to a kHz background. A careful electrode design must therefore ensure that no Penning traps appear in the entire KATRIN system. Background due to stored electrons arising from 220Rn and 219Rn alpha-decay and Tritium beta-decay in the volume of the main spectrometer is the anticipated main background source. A single nuclear decay can produce an enhanced background level for up to 10 hours. To alleviate the background arising from stored electrons, a novel method based on stochastic heating by using the technique of electron cyclotron resonance (ECR) will be applied. Both measurements and corresponding simulations demonstrate that a high frequency eld tuned to the cyclotron frequency of the stored electrons breaks their storage condition by stochastic heating within less than 5 ms. This method will allow for an almost background free spectrometer. The talk will give an overview of the status of the KATRIN experiment and will mainly focus on the background issues described above.