Karlsruhe Tritium Experiment: Detector System Commissioning and In-Situ PIN-Diode Array Dead-Layer Measurement
Wall, Brandon Lee
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The <underline>Ka</underline>rlsruhe <underline>Tri</underline>tium <underline>N</underline>eutrino (KATRIN) experimental goal is to measure the neutrino mass to 0.2 eV sensitivity at the 90 percent confidence level. This is an order of magnitude more sensitive than the two most recent direct neutrino mass measurements. The primary sensitivity of the KATRIN experiment is determined by the source strength and the main spectrometer resolution, but a confluence of focal plane detector parameters contribute to the uncertainty in the measured neutrino mass including the detector backgrounds and the detector electron response function. The detector system group developed a figure of demerit, <italic>F</italic>, to quantify the effect of the detector system on neutrino mass uncertainty. <italic>F</italic>, essentially a signal to noise ratio, weights the focal plane detector response function against the total background based upon their influence of the <italic>m<super>2</super><sub>ν</sub></italic> uncertainty. During commissioning of the detector system at the University of Washington, we determined a figure of demerit value of 1.12 ± .01, which nearly meets the tritium data taking goal for KATRIN. A critical parameter that effects the detector response is the focal plane detector's dead layer. The KATRIN detector system's design constraints needed a novel approach to measure the dead-layer thickness not outlined in standard texts. We used a method of making measurements with an electron source over a range of incident energies, and then fit these monoenergetic electron source spectra to simulated spectra to determine the dead-layer thickness of the KATRIN focal plane detector. The standard model of a monolithic dead layer yielded poor overall fits, while a model that allowed the energy deposited into the dead layer to diffuse back into the active region, gave an improved fit, with a preferred value of 46%. Using this model, the final detector dead layer thickness of the focal plane detector is 1554±5 (Stat.) <super>+18.8</super><sub>-12.4</sub> (Syst.) Å.
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