University thesis:
Dissertation, Universität Freiburg, 2021
Footnote:
Description:
Abstract: Many astrophysical and cosmological observations support the hypothesis that the Universe is made by a considerable amount of cold dark matter. One of the most popular dark matter candidate is the weakly interacting massive particle (WIMP). WIMP detection is the primarily goal of the XENON Project, which employs xenon dual-phase (Liquid/Gas) Time Projection Chambers (TPC) at the Italian LNGS laboratory.<br>The XENON1T detector, operating until 2018, was upgraded to XENONnT during a 2 years long operation, which included the decommissioning of the XENON1T TPC, the upgrade of several subsystems and the assembly of the new XENONnT TPC. These operations are described in detail in this work. XENONnT aims to probe spin-independent WIMP-nucleon cross sections of 1.4 × 10−48 cm2 for a 50 GeV/c2 mass WIMP at 90% C.L., for this purpose it requires a very low background level. One of the major sources of background is 222Rn and the subsequent β-decays of its progenies, in particular of 214Pb.<br>In this work, an analysis of the α-decays of the mother and daughter isotope of 214Pb was performed and an activity concentration of 214Pb between (1.7 ± 0.1) and (3.4 ± 0.1) μBq/kg was measured.<br>XENONnT can also be utilised for the search for the neutrinoless double beta decay (0νββ) of 136Xe, a nuclear transition predicted by extensions of the Standard Model but not observed yet. Its detection would prove the violation of the total lepton number, the Majorana nature of neutrinos and it could provide information on the neutrino mass ordering.<br>The XENONnT half-life sensitivity to 0νββ-decay of 136Xe was assessed in this work and is 3.9 × 1025 yr at 90% C.L.. This result is not competitive with dedicated 0νββ experiments, however it shows the potential of XENONnT to investigate the 0νββ-decay, broadening the science program beyond low energy studies of WIMPs