The SIMPLE Phase II Dark Matter Search

Abstract

Phase II of SIMPLE (Superheated Instrument for Massive ParticLe Experiments) searched for astroparticle dark matter using superheated liquid C${}_2$ClF${}_5$ droplet detectors. Each droplet generally requires an energy deposition with linear energy transfer (LET) $\gtrsim$ 150 keV/$\mu$m for a liquid-to-gas phase transition, providing an intrinsic rejection against minimum ionizing particles of order 10${}^{-10}$, and reducing the backgrounds to primarily $\alpha$ and neutron-induced recoil events. The droplet phase transition generates a millimetric-sized gas bubble which is recorded by acoustic means. We describe the SIMPLE detectors, their acoustic instrumentation, and the characterizations, signal analysis and data selection which yield a particle-induced, "true nucleation" event detection efficiency of better than 97% at a 95% C.L. The recoil-$\alpha$ event discrimination, determined using detectors first irradiated with neutrons and then doped with alpha emitters, provides a recoil identification of better than 99%; it differs from those of COUPP and PICASSO primarily as a result of their different liquids with lower critical LETs. The science measurements, comprising two shielded arrays of fifteen detectors each and a total exposure of 27.77 kgd, are detailed. Removal of the 1.94 kgd Stage 1 installation period data, which had previously been mistakenly included in the data, reduces the science exposure from 20.18 to 18.24 kgd and provides new contour minima of ${\sigma }_p$ = 4.3 $\times$ 10${}^{-3}$ pb at 35 GeV/c${}^2$ in the spin-dependent sector of WIMP-proton interactions and ${\sigma }_N$ = 3.6 $\times$ 10${}^{-6}$ pb at 35 GeV/c${}^2$ in the spin-independent sector. These results are examined with respect to the fluorine spin and halo parameters used in the previous data analysis.

20 pages, 19 figures; accepted Physical Review D

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Cited by in corpus (8)

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• Constraining the Spin-Dependent WIMP-Nucleon Cross Sections with XENON1T
• Final Results of the PICASSO Dark Matter Search Experiment
• Nuclear spin-dependent interactions: Searches for WIMP, Axion and Topological Defect Dark Matter, and Tests of Fundamental Symmetries
• Light mediators in dark matter direct detections
• Dark Matter phenomenology : from simplified WIMP models to refined alternative solutions
• Chromo-Rayleigh Interactions of Dark Matter