KArlsruhe TRItium Neutrino Experiment (KATRIN) detector and backgrounds

One of the more surprising discoveries of the past century is that neutrinos have non-zero mass, but measuring the absolute scale of the neutrino's mass has proven to be very challenging. The KArlsruhe TRItium Neutrino (KATRIN) experiment is dedicated to measuring or limiting the electron-type neutrino's effective mass. By analyzing the energy spectrum of electrons emitted in tritium beta decay, KATRIN is sensitive to masses as low as 0.20 eV with a 90$\%$ CL, an order-of-magnitude better than the current direct limit. KATRIN can achieve this sensitivity because of its highly luminous source, large acceptance Main Spectrometer with extremely accurate energy resolution, and efficient silicon detector with minimal backgrounds. Extensive Geant4 simulations of the silicon detector's intrinsic backgrounds were used to optimize the detector region design and indicate that these backgrounds are compatible with our projected sensitivity. The design goal is 1 mHz background in our region of interest for a 500 micron, 4.5 cm radius segmented silicon detector. For this experiment at the surface of the earth, the major backgrounds will be cosmic rays and natural radioactivity. Verification and results of simulations will be presented.