Phys. Rev. D 93, 052014 (2016) 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 a second run of the 2-liter PICO-2L C\(_3\)F\(_8\) bubble chamber with a total exposure of 129\(\,\)kg-days at a thermodynamic threshold energy of 3.3\(\,\)keV. These data ...show that measures taken to control particulate contamination in the superheated fluid resulted in the absence of the anomalous background events observed in the first run of this bubble chamber. One single nuclear-recoil event was observed in the data, consistent both with the predicted background rate from neutrons and with the observed rate of unambiguous multiple-bubble neutron scattering events. The chamber exhibits the same excellent electron-recoil and alpha decay rejection as was previously reported. These data provide the most stringent direct detection constraints on weakly interacting massive particle (WIMP)-proton spin-dependent scattering to date for WIMP masses \(<\) 50\(\,\)GeV/c\(^2\).
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.
Final results are reported from operation of the PICO-60 C\(_3\)F\(_8\) dark matter detector, a bubble chamber filled with 52 kg of C\(_3\)F\(_8\) located in the SNOLAB underground laboratory. The ...chamber was operated at thermodynamic thresholds as low as 1.2 keV without loss of stability. A new blind 1404-kg-day exposure at 2.45 keV threshold was acquired with approximately the same expected total background rate as the previous 1167-kg-day exposure at 3.3 keV. This increased exposure is enabled in part by a new optical tracking analysis to better identify events near detector walls, permitting a larger fiducial volume. These results set the most stringent direct-detection constraint to date on the WIMP-proton spin-dependent cross section at 2.5 \(\times\) 10\(^{-41}\) cm\(^2\) for a 25 GeV WIMP, and improve on previous PICO results for 3-5 GeV WIMPs by an order of magnitude.
New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of C\(_3\)F\(_8\) located in the SNOLAB underground laboratory. As in previous PICO ...bubble chambers, PICO-60 C\(_3\)F\(_8\) exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than 1 event per month. A blind analysis of an efficiency-corrected 1167-kg-day exposure at a 3.3-keV thermodynamic threshold reveals no single-scattering nuclear recoil candidates, consistent with the predicted background. These results set the most stringent direct-detection constraint to date on the WIMP-proton spin-dependent cross section at 3.4 \(\times\) 10\(^{-41}\) cm\(^2\) for a 30-GeV\(\thinspace\)c\(^{-2}\) WIMP, more than one order of magnitude improvement from previous PICO results.
Recent results from the PICASSO dark matter search experiment at SNOLAB are reported. These results were obtained using a subset of 10 detectors with a total target mass of 0.72 kg of 19F and an ...exposure of 114 kgd. The low backgrounds in PICASSO allow recoil energy thresholds as low as 1.7 keV to be obtained which results in an increased sensitivity to interactions from Weakly Interacting Massive Particles (WIMPs) with masses below 10 GeV/c^2. No dark matter signal was found. Best exclusion limits in the spin dependent sector were obtained for WIMP masses of 20 GeV/c^2 with a cross section on protons of sigma_p^SD = 0.032 pb (90% C.L.). In the spin independent sector close to the low mass region of 7 GeV/c2 favoured by CoGeNT and DAMA/LIBRA, cross sections larger than sigma_p^SI = 1.41x10^-4 pb (90% C.L.) are excluded.
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.
