A New and Improved Spin-Dependent Dark Matter Exclusion Limit Using the PICASSO Experiment.

摘要

The PICASSO project is a direct dark matter search experiment located 2070 metres underground in SNOLAB. Superheated droplets of Freon (C4 F10) are used as the active mass, providing a target for the incoming neutralinos. Recoiling nuclei deposit energy in the superheated Freon droplets, triggering a phase transition, the pressure waves of which can be detected using piezo-electric sensors.;In addition, a thorough study of the backgrounds, corrections and systematic uncertainties has been included, indicating that this limit does not exceed 3.5x10-2 pb when considering the one sigma error on the uncertainty band.;Previously published limits using an exposure of 1.98+/-0.19 kg day obtained a peak spin-dependent cross section exclusion limit for neutralino-proton interactions of 1.31 pb at a neutralino mass of 29 GeV/c2 at a 90% confidence level (1). Improvements in the detectors installed in the underground experiment have provided 20.99+/-0.25 kg day for analysis and improvements in the analysis method have produced an exclusion limit of 2.9x10-2 pb at a neutralino mass of 16.7 GeV/c2.