Prospects for SIMPLE 2000: a large-mass, low-background superheated droplet detector for WIMP searches

The Superheated Instrument for Massive Particle searches (SIMPLE 2000) will consist of an array of 8–16 large active mass ( 15 g) superheated droplet detectors (SDDs) to be installed in the new underground laboratory of Rustrel-Pays d’Apt. Several factors make the use of SDDs an attractive approach for the detection of weakly interacting massive particles (WIMPs), namely their intrinsic insensitivity to minimally ionizing particles, high fluorine content, low cost and operation at near ambient pressure and temperature. We comment here on the fabrication, calibration and already-competitive first limits from prototype SDDs for SIMPLE, as well as on the expected immediate increase in sensitivity of the programme, which aims at an exposure of >25 kg day during 2000. The ability of modest-mass fluorine-rich detectors to investigate regions of neutralino parameter space beyond the reach of the most ambitious cryogenic projects is pointed out. Apfel extended the bubble chamber concept by the invention of superheated droplet detectors [1] (SDDs, also known as bubble detectors), a dispersion of small drops (radius 10 μm) of New Journal of Physics 2 (2000) 14.1–14.14 PII: S1367-2630(00)12345-6 1367-2630/00/000014+14$30.00 © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft