There is almost universal agreement that most of the mass in the Universe consists of dark matter. Many lines of reasoning suggest that the dark matter consists of a weakly interactive massive particle (WIMP) with mass ranging from 10 GeV/c2 to a few TeV/c2. Today, numerous experiments aim for direct or indirect dark matter detection.;XENON10 is a direct detection experiment using a xenon dual phase time projection chamber. Particles interacting with xenon will create a scintillation signal (S1) and ionization. The charge produced is extracted into the gas phase and converted into a proportional scintillation light ( S2), with an external electric field. The dominant background, beta particles and gamma rays, will undergo an electron recoil (ER) interaction, while WIMPs and neutrons will undergo a nuclear recoil (NR) interaction. Event-by-event discrimination of background signals is based on log10( S2/S1)NR log 10(S2/S1)ER and the 3-D position reconstruction. In 2006 the XENON10 detector started underground operations at laboratorio Nazionali del Gran Sasso in Italy. After 6 months of operations, totaling 58.6 live days and 5.4 kg of fiducial mass, XENON10 set the best upper limits at the time. Finding a spin-independent WIMP-nucleon cross-section sigmachi = 8.8 x 10 -44 cm2 and a spin-dependent WIMP-neutron cross-section sigma chi = 1.0 x 10-38 cm2 for a WIMP mass of 100 GeV/c2 (90% C.L.).;In this work I give an overview of the dark matter evidence and review the requirements for a dark matter search. In particular I discuss the XENON10 detector, deployment, operation, calibrations, analysis and WIMP-nucleon cross-section limits. Finally, I present our latest results for the relative scintillation efficiency ( Leff ) for nuclear recoils in liquid xenon, which was the biggest source of uncertainty in the XENON10 limit. This quantity is essential to determine the nuclear energy scale and to determine the WIMP-nucleon cross sections.
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