New results are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 52 kg of ${\mathrm{C}}_3{\mathrm{F}}_8$ located in the SNOLAB underground laboratory. As in previous PICO bubble chambers, $\mathrm{PICO}\text{−}60{\mathrm{C}}_3{\mathrm{F}}_8$ exhibits excellent electron recoil and alpha decay rejection, and the observed multiple-scattering neutron rate indicates a single-scatter neutron background of less than one 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 weakly interacting massive particle (WIMP)-proton spin-dependent cross section at $3.4\times {10}^{-41}{\mathrm{cm}}^2$ for a $30\text{−}\mathrm{GeV}{\mathrm{c}}^{-2}$ WIMP, more than 1 order of magnitude improvement from previous PICO results.

We report the discovery of four Fast Radio Bursts (FRBs) in the ongoing SUrvey for Pulsars and Extragalactic Radio Bursts at the Parkes Radio Telescope: FRBs 150610, 151206, 151230 and 160102. Our real-time discoveries have enabled us to conduct extensive, rapid multimessenger follow-up at 12 major facilities sensitive to radio, optical, X-ray, gamma-ray photons and neutrinos on time-scales ranging from an hour to a few months post-burst. No counterparts to the FRBs were found and we provide upper limits on afterglow luminosities. None of the FRBs were seen to repeat. Formal fits to all FRBs show hints of scattering while their intrinsic widths are unresolved in time. FRB 151206 is at low Galactic latitude, FRB 151230 shows a sharp spectral cut-off, and FRB 160102 has the highest dispersion measure (DM = 2596.1 ± 0.3 pc cm⁻³) detected to date. Three of the FRBs have high dispersion measures (DM > 1500 pc cm⁻³), favouring a scenario where the DM is dominated by contributions from the intergalactic medium. The slope of the Parkes FRB source counts distribution with fluences >2 Jy ms is $$\alpha =-2.2^{+0.6}_{-1.2}$$ and still consistent with a Euclidean distribution (α = −3/2). We also find that the all-sky rate is $$1.7^{+1.5}_{-0.9}\times 10^3$$FRBs/(4π sr)/day above $${\sim }2{\rm \, }\rm {Jy}{\rm \, }\rm {ms}$$ and there is currently no strong evidence for a latitude-dependent FRB sky rate.

New data are reported from the operation of the PICO-60 dark matter detector, a bubble chamber filled with 36.8 kg of ${\mathrm{CF}}_3\mathrm{I}$ 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 ${\mathrm{C}}_3{\mathrm{F}}_8$ 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 ${\mathrm{C}}_3{\mathrm{F}}_8$ bubble chamber in the SNOLAB underground laboratory, with a total exposure of 211.5 kg days at four different energy thresholds below 10 keV. These data show that ${\mathrm{C}}_3{\mathrm{F}}_8$ provides excellent electron-recoil and alpha rejection capabilities at very low thresholds. The chamber exhibits an electron-recoil sensitivity of $<3.5\times 10^{-10}$ and an alpha rejection factor of $>98.2\%$. These data also include 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.

New data are reported from a second run of the 2-liter PICO-2L ${\mathrm{C}}_3{\mathrm{F}}_8$ 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 $<50\mathrm{GeV}/{\mathrm{c}}^2$.