Viktor Zacek
Universite de Montreal

Status of the PICASSO Dark Matter Search Project

The nature of the main constituents of the mass of the universe is one of the 
outstanding riddles of cosmology and astro-particle physics. Current models 
explaining the evolution of the universe, and measurements of the various 
components of its mass, all have in common that an appreciable contribution to 
that mass is non-luminous and non-baryonic, and that a large fraction of this 
so-called dark matter must be in the form of non-relativistic massive 
particles (Cold Dark Matter: CDM). The PICASSO  dark matter detector is based 
on the phase transition induced by nuclear recoils in superheated droplets. 
This technique is a promising alternative to other, more conventional detector 
approaches and has an interesting background suppression feature: we could 
show that, depending on the temperature of operation, the detector can be 
either fully sensitive to CDM or completely insensitive to nuclear recoils 
produced by neutralinos, while responding in a well understood manner to 
residual background, such as that produced by alpha-emitting contaminations 
of the detector material. A pilot experiment with six detectors and 100g 
active mass is presently taking data at the Sudbury underground laboratory 
and we will discuss ongoing work to decrease radioactive background and to 
increase the size of the detector modules.