Phys. Rev. Lett. 114, 231302 (2015) New data are reported from the operation of a 2-liter C$_3$F$_8$ bubble
chamber in the 2100 meter deep SNOLAB underground laboratory, with a total
exposure of ...211.5 kg-days at four different recoil energy thresholds ranging
from 3.2 keV to 8.1 keV. These data show that C3F8 provides excellent electron
recoil and alpha rejection capabilities at very low thresholds, including the
first observation of a dependence of acoustic signal on alpha energy. Twelve
single nuclear recoil event candidates were observed during the run. The
candidate events exhibit timing characteristics that are not consistent with
the hypothesis of a uniform time distribution, and no evidence for a dark
matter signal is claimed. These data provide 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.
We report on a search for Weakly Interacting Massive Particles (WIMPs) using 278.8 days of data collected with the XENON1T experiment at LNGS. XENON1T utilizes a liquid xenon time projection chamber ...with a fiducial mass of \((1.30 \pm 0.01)\) t, resulting in a 1.0 t\(\times\)yr exposure. The energy region of interest, 1.4, 10.6 \(\mathrm{keV_{ee}}\) (4.9, 40.9 \(\mathrm{keV_{nr}}\)), exhibits an ultra-low electron recoil background rate of \((82\substack{+5 \\ -3}\textrm{ (sys)}\pm3\textrm{ (stat)})\) events/\((\mathrm{t}\times\mathrm{yr}\times\mathrm{keV_{ee}})\). No significant excess over background is found and a profile likelihood analysis parameterized in spatial and energy dimensions excludes new parameter space for the WIMP-nucleon spin-independent elastic scatter cross-section for WIMP masses above 6 GeV/c\({}^2\), with a minimum of \(4.1\times10^{-47}\) cm\(^2\) at 30 GeV/c\({}^2\) and 90% confidence level.
New data are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 36.8 kg of CF\(_3\)I and located in the SNOLAB underground laboratory. PICO-60 is the ...largest bubble chamber to search for dark matter to date. With an analyzed exposure of 92.8 livedays, PICO-60 exhibits the same excellent background rejection observed in smaller bubble chambers. Alpha decays in PICO-60 exhibit frequency-dependent acoustic calorimetry, similar but not identical to that reported recently in a C\(_3\)F\(_8\) bubble chamber. PICO-60 also observes a large population of unknown background events, exhibiting acoustic, spatial, and timing behaviors inconsistent with those expected from a dark matter signal. These behaviors allow for analysis cuts to remove all background events while retaining \(48.2\%\) of the exposure. Stringent limits on weakly interacting massive particles interacting via spin-dependent proton and spin-independent processes are set, and most interpretations of the DAMA/LIBRA modulation signal as dark matter interacting with iodine nuclei are ruled out.
New data are reported from the operation of a 2-liter C\(_3\)F\(_8\) bubble chamber in the 2100 meter deep SNOLAB underground laboratory, with a total exposure of 211.5 kg-days at four different ...recoil energy thresholds ranging from 3.2 keV to 8.1 keV. These data show that C3F8 provides excellent electron recoil and alpha rejection capabilities at very low thresholds, including the first observation of a dependence of acoustic signal on alpha energy. Twelve single nuclear recoil event candidates were observed during the run. The candidate events exhibit timing characteristics that are not consistent with the hypothesis of a uniform time distribution, and no evidence for a dark matter signal is claimed. These data provide 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.
