Search

Abstract: We present results of systematic studies of the radiation response of superheated liquid droplet detectors, which are used in the PICASSO dark matter search experiment. This detection technique is based on the phase transitions of superheated liquid Freon droplets dispersed and trapped in a polymerized gel. Phase transitions can be induced by nuclear recoils following particle interactions and, in particular, interactions with Weakly Interacting Massive Particles (WIMPs). These detectors are threshold devices since a minimal energy deposition is necessary to induce a phase transition and their sensitivity to various types of radiation depends strongly on the operating temperature and pressure. The sensitivity to neutrons, α-particles and γ-rays was determined as a function of these operating parameters and the results are compared with simulations. In particular, we present a complete characterization of the response of detector modules already in use for a dark matter search at the SNO site to detect WIMPs and discuss possible background sources. [Copyright &y& Elsevier]

Abstract: The PICASSO experiment reports an improved limit for the existence of cold dark matter WIMPs interacting via spin-dependent interactions with nuclei. The experiment is installed in the Sudbury Neutrino Observatory at a depth of 2070 m. With superheated C4F10 droplets as the active material, and an exposure of , no evidence for a WIMP signal was found. For a WIMP mass of 29 GeV, limits on the spin-dependent cross section on protons of and on neutrons of have been obtained at 90% C.L. In both cases, some new parameter space in the region of WIMP masses below 20 GeV has now been ruled out. The results of these measurements are also presented in terms of limits on the effective WIMP-proton and neutron coupling strengths and . [Copyright &y& Elsevier]

Abstract: The MUNU detector was designed to study elastic scattering at low energy. The central component is a Time Projection Chamber filled with CF4 gas, surrounded by an anti-Compton detector. The experiment was carried out at the Bugey (France) nuclear reactor. In this Letter we present the final analysis of the data recorded at 3 bar and 1 bar pressure. Both the energy and the scattering angle of the recoil electron are measured. From the 3 bar data a new upper limit on the neutrino magnetic moment at 90% CL was derived. At 1 bar electron tracks down to 150 keV were reconstructed, demonstrating the potentiality of the experimental technique for future applications in low energy neutrino physics. [Copyright &y& Elsevier]

Several techniques have been investigated to achieve good amplification in gas Time Projection Chambers. The classical Micromegas detection scheme with nickel grid is compared with a new one, with a stainless steel woven wire mesh, in CF4 at different operating pressures. The performances and the mechanical properties of the woven wire mesh make this solution attractive for low and high energy particle physics experiments and other applications like low dose radiography. A more detailed study appears in Jeanneret (Ph.D. Thesis, Neuchaˆtel University, 2001). [Copyright &y& Elsevier]