Final Analysis and Results of the Phase II SIMPLE Dark Matter Search

Abstract

We report the final results of the Phase II SIMPLE measurements, comprising two run stages of 15 superheated droplet detectors each, with the second stage including an improved neutron shielding. The analyses include a refined signal analysis, and revised nucleation efficiency based on a reanalysis of previously reported monochromatic neutron irradiations. The combined results yield a contour minimum of ${\ensuremath{\sigma}}_{p}=5.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{pb}$ at $35\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ in the spin-dependent sector of weakly interacting massive particle (WIMP) proton interactions, the most restrictive to date for ${M}_{W}\ensuremath{\le}60\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ from a direct search experiment and overlapping, for the first time, with results previously obtained only indirectly. In the spin-independent sector, a minimum of $4.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}\text{ }\text{ }\mathrm{pb}$ at $35\text{ }\text{ }\mathrm{GeV}/{c}^{2}$ is achieved, with the exclusion contour challenging a significant part of the light mass WIMP region of current interest.