New Results from the PICO Dark Matter Search Experiment

The PICO Collaboration has made considerable progress in the development of bubble nucleation in superheated fluids as a tool in the search for WIMP dark matter. The physics of bubble nucleation allows for the sensitive detection of nuclear recoils, while being largely insensitive to backgrounds from gamma and beta radiation. Recently published results using a perfluoro-propane (C3F8) target in a 2-liter bubble chamber have provided the most sensitive direct detection constraints on WIMP-proton spin-dependent scattering to date, with significant sensitivity at low WIMP masses for spin-independent WIMP-nucleon scattering. The technology has, however, been limited by unexplained backgrounds. Over the past year, considerable progress has been made in identifying and eliminating the sources of anomalous background events. Crisler has recently completed a new 190 kg-day exposure of the modified PICO-2L bubble chamber operating with a 3 KeV threshold. Results from the new run will be presented.