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dc.contributor.advisorMurphy, Alex
dc.contributor.advisorGhag, Chamkaur
dc.contributor.authorReichhart, Lea
dc.date.accessioned2013-10-17T14:39:00Z
dc.date.available2013-10-17T14:39:00Z
dc.date.issued2013-11-28
dc.identifier.urihttp://hdl.handle.net/1842/7914
dc.description.abstractAstrophysical observations give convincing evidence for a vast non-baryonic component, the so-called dark matter, accounting for over 20% of the overall content of our Universe. Direct dark matter search experiments explore the possibility of interactions of these dark matter particles with ordinary baryonic matter via elastic scattering resulting in single nuclear recoils. The ZEPLIN-III detector operated on the basis of a dualphase (liquid/gas) xenon target, recording events in two separate response channels { scintillation and ionisation. These allow discrimination between electron recoils (from background radiation) and the signal expected from Weakly Interacting Massive Particle (WIMP) elastic scatters. Following a productive first exposure, the detector was upgraded with a new array of ultra-low background photomultiplier tubes, reducing the electron recoil background by over an order of magnitude. A second major upgrade to the detector was the incorporation of a tonne-scale active veto detector system, surrounding the WIMP target. Calibration and science data taken in coincidence with ZEPLIN-III showed rejection of up to 30% of the dominant electron recoil background and over 60% of neutron induced nuclear recoils. Data taking for the second science run finished in May 2011 with a total accrued raw fiducial exposure of 1,344 kg days. With this extensive data set, from over 300 days of run time, a limit on the spin-independent WIMP-nucleon cross-section of 4.8 10-8 pb near 50 GeV/c2 WIMP mass with 90% confidence was set. This result combined with the first science run of ZEPLIN-III excludes the scalar cross-section above 3.9 10-8 pb. Studying the background data taken by the veto detector allowed a calculation of the neutron yield induced by high energy cosmic-ray muons in lead of (5.8 0.2) 10-3 neutrons/muon/(g/cm2) for a mean muon energy of 260 GeV. Measurements of this kind are of great importance for large scale direct dark matter search experiments and future rare event searches in general. Finally, this work includes a comprehensive measurement of the energy dependent quenching factor for low energy nuclear recoils in a plastic scintillator, such as from the ZEPLIN-III veto detector, increasing accuracy for future simulation packages featuring large scale plastic scintillator detector systems.en_US
dc.language.isoenen_US
dc.publisherThe University of Edinburghen_US
dc.relation.hasversionL. Reichhart et al. Measurement and simulation of the muon-induced neutron yield in lead. arXiv:1302.4275v1 [physics.ins-det], submitted to Astroparticle Physics, 2013.en_US
dc.relation.hasversionL. Reichhart et al., Quenching Factor for Low Energy Nuclear Recoils in a Plastic Scintillator. In Physical Review C 85:065801, 2012.en_US
dc.subjectdark matteren_US
dc.subjectZEPLIN-IIIen_US
dc.subjectWIMPsen_US
dc.subjectliquid xenon detectorsen_US
dc.subjectveto detectoren_US
dc.subjectplastic scintillatoren_US
dc.subjectquenchingen_US
dc.subjectcosmic ray muonsen_US
dc.subjectneutronsen_US
dc.subjectMonte Carlo simulationsen_US
dc.titleZEPLIN-III direct dark matter search : final results and measurements in support of next generation instrumentsen_US
dc.typeThesis or Dissertationen_US
dc.type.qualificationlevelDoctoralen_US
dc.type.qualificationnamePhD Doctor of Philosophyen_US


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