Use of micro-structured filters to explore the KATRIN background

The key goal of the KATRIN experiment is the measurement of the absolute mass scale of neutrinos with an unprecedented sensitivity of better than 0.3 eV/c2. Currently, the measured background level exceeds the design value, wherefore a detailed understanding of background processes in the large main spectrometer is required. According to our prior model, background events originate from Hydrogen Rydberg states, generated by the decay of surface-implanted 210Pb, on the main spectrometer vessel surface. Thermal radiation can ionise such long-lived, highly excited states, resulting in low-energy electrons on the meV-scale. These are then accelerated by the retarding potential, thus possess small transverse energy, which is in contrast to signal beta-electrons. We have performed measurements with a passive transverse energy filter (pTEF) implemented as a micro-structured honeycomb gold plate.
This talk discusses the observed transmission of background electrons through the pTEF at different magnetic field values and compares the initial and refined background model.
This work is supported by the Helmholtz Association and by the Ministry for Education and Research BMBF (grant numbers 05A23PMA, 05A23PX2, 05A23VK2, and 05A23WO6)