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Intrinsic 85Kr and 222Rn Backgrounds in the XENON Dark Matter Search

Lindemann, Sebastian

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The XENON Dark Matter search is aiming for the direct detection of Dark Matter in the form of weakly interacting massive particles (WIMPs) scattering off xenon nuclei. This process is expected to be extremely rare, if at all existing. To be detectable, competing background has to be suppressed to unprecedented level. This defines the framework for this thesis. First, the data analysis is sketched that resulted in todays strongest limit on the spin-independent WIMPnucleon scattering for WIMP masses above 8 GeV/c2 using an exposure of 225 live days x 34 kg collected by the Xenon100 detector. For this analysis we develop a successfully employed consistency condition rejecting non-physical background. In the main part of this thesis, we investigate the intrinsic backgrounds 85Kr and 222Rn. To be sensitive to a potential WIMP signal, ultra-low concentrations have to be achieved in the liquid xenon target. We developed a method to determine krypton traces in xenon above a detection limit of only 6 parts per quadrillion (ppq) - two orders of magnitude below previous achievements. We prove that the cryogenic fractional distillation reaches a krypton level in xenon below 1 parts per tril (ppt). This represents a crucial proof-of-principle for the needs of the upcoming Xenon1T detector. Moreover, we present a 222Rn emanation assay of the Xenon100 detector and apply our results to cast projections on the future background handling in Xenon1T. Finally, we introduce two promising realizations of radon removal systems and argue for the utmost importance of 222Rn emanation assays.

Item Type: Dissertation
Supervisor: Hampel, Prof. Dr. Wolfgang
Place of Publication: Heidelberg
Date of thesis defense: 13 November 2013
Date Deposited: 19 Nov 2013 10:28
Date: 2013
Faculties / Institutes: The Faculty of Physics and Astronomy > Dekanat der Fakultät für Physik und Astronomie
Subjects: 530 Physics
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