We present the results of a search for dark matter weakly interacting massive particles (WIMPs) in the mass range below $20\mathrm{GeV}/c^2$ using a target of low-radioactivity argon with a 6786.0 kg d exposure. The data were obtained using the DarkSide-50 apparatus at Laboratori Nazionali del Gran Sasso. The analysis is based on the ionization signal, for which the DarkSide-50 time projection chamber is fully efficient at $0.1\mathrm{keV}\text{ee}$. The observed rate in the detector at $0.5\mathrm{keV}\text{ee}$ is about $1.5\mathrm{event}/\mathrm{keV}\text{ee}/\mathrm{kg}/\mathrm{d}$ and is almost entirely accounted for by known background sources. We obtain a 90% C.L. exclusion limit above $1.8\mathrm{GeV}/c^2$ for the spin-independent cross section of dark matter WIMPs on nucleons, extending the exclusion region for dark matter below previous limits in the range $1.8–6\mathrm{GeV}/c^2$.

The NOvA experiment has seen a $4.4\sigma$ signal of ${\overline{\nu }}_e$ appearance in a 2 GeV ${\overline{\nu }}_{\mu }$ beam at a distance of 810 km. Using $12.33\times {10}^{20}$ protons on target delivered to the Fermilab NuMI neutrino beamline, the experiment recorded 27 ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_e$ candidates with a background of 10.3 and 102 ${\overline{\nu }}_{\mu }\to {\overline{\nu }}_{\mu }$ candidates. This new antineutrino data are combined with neutrino data to measure the parameters $|\mathrm{\Delta }{m}_{32}^2|=2.48_{-0.06}^{+0.11}\times {10}^{-3}{\mathrm{eV}}^2/c^4$ and ${\sin }^2{\theta }_{23}$ in the ranges from (0.53–0.60) and (0.45–0.48) in the normal neutrino mass hierarchy. The data exclude most values near ${\delta }_{CP}=\pi /2$ for the inverted mass hierarchy by more than $3\sigma$ and favor the normal neutrino mass hierarchy by $1.9\sigma$ and ${\theta }_{23}$ values in the upper octant by $1.6\sigma$.

We present new constraints on sub-GeV dark-matter particles scattering off electrons based on 6780.0 kg d of data collected with the DarkSide-50 dual-phase argon time projection chamber. This analysis uses electroluminescence signals due to ionized electrons extracted from the liquid argon target. The detector has a very high trigger probability for these signals, allowing for an analysis threshold of three extracted electrons, or approximately 0.05 keVee. We calculate the expected recoil spectra for dark matter-electron scattering in argon and, under the assumption of momentum-independent scattering, improve upon existing limits from XENON10 for dark-matter particles with masses between 30 and $100\mathrm{MeV}/c^2$.

The DarkSide-50 direct-detection dark matter experiment is a dual-phase argon time projection chamber operating at Laboratori Nazionali del Gran Sasso. This paper reports on the blind analysis of a $(16660\pm 270)\mathrm{kg}\mathrm{d}$ exposure using a target of low-radioactivity argon extracted from underground sources. We find no events in the dark matter selection box and set a 90% C.L. upper limit on the dark matter–nucleon spin-independent cross section of $1.14\times {10}^{-44}{\mathrm{cm}}^2$ ($3.78\times {10}^{-44}{\mathrm{cm}}^2$, $3.43\times {10}^{-43}{\mathrm{cm}}^2$) for a WIMP mass of $100\mathrm{GeV}/c^2$ ($1\mathrm{TeV}/c^2$, $10\mathrm{TeV}/c^2$).

We report results from the first search for ${\nu }_{\mu }\to {\nu }_e$ transitions by the NOvA experiment. In an exposure equivalent to $2.74\times {10}^{20}$ protons on target in the upgraded NuMI beam at Fermilab, we observe 6 events in the Far Detector, compared to a background expectation of $0.99\pm 0.11(\text{syst})$ events based on the Near Detector measurement. A secondary analysis observes 11 events with a background of $1.07\pm 0.14(\text{syst})$. The $3.3\sigma$ excess of events observed in the primary analysis disfavors $0.1\pi <{\delta }_{CP}<0.5\pi$ in the inverted mass hierarchy at the 90% C.L.