Liquid argon is a bright scintillator with potent particle identification properties, making it an attractive target for direct-detection dark matter searches. The DarkSide-50 dark matter search here reports the first WIMP search results obtained using a target of low-radioactivity argon. DarkSide-50 is a dark matter detector, using a two-phase liquid argon time projection chamber, located at the Laboratori Nazionali del Gran Sasso. The underground argon is shown to contain ${}^{39}\mathrm{Ar}$ at a level reduced by a factor $(1.4\pm 0.2)\times {10}^3$ relative to atmospheric argon. We report a background-free null result from $(2616\pm 43)\mathrm{kg}\mathrm{d}$ of data, accumulated over 70.9 live days. When combined with our previous search using an atmospheric argon, the 90% C.L. upper limit on the WIMP-nucleon spin-independent cross section, based on zero events found in the WIMP search regions, is $2.0\times {10}^{-44}{\mathrm{cm}}^2$ ($8.6\times {10}^{-44}{\mathrm{cm}}^2$, $8.0\times {10}^{-43}{\mathrm{cm}}^2$) for a WIMP mass of $100\mathrm{GeV}/c^2$ ($1\mathrm{TeV}/c^2$, $10\mathrm{TeV}/c^2$).

A consistent generalization of statistical mechanics is obtained by applying the maximum entropy principle to a trace-form entropy and by requiring that physically motivated mathematical properties are preserved. The emerging differential-functional equation yields a two-parameter class of generalized logarithms, from which entropies and power-law distributions follow: these distributions could be relevant in many anomalous systems. Within the specified range of parameters, these entropies possess positivity, continuity, symmetry, expansibility, decisivity, maximality, concavity, and are Lesche stable. The Boltzmann-Shannon entropy and some one-parameter generalized entropies already known belong to this class. These entropies and their distribution functions are compared, and the corresponding deformed algebras are discussed.

We predict geoneutrino fluxes in a reference model based on a detailed description of Earth’s crust and mantle and using the best available information on the abundances of uranium, thorium, and potassium inside Earth’s layers. We estimate the uncertainties of fluxes corresponding to the uncertainties of the element abundances. In addition to distance integrated fluxes, we also provide the differential fluxes as a function of distance from several sites of experimental interest. Event yields at several locations are estimated and their dependence on the neutrino oscillation parameters is discussed. At Kamioka we predict $N(\mathrm{U}+\mathrm{Th})=35\mathrm{}\pm 6$ events for ${10}^{32}\mathrm{proton}\mathrm{yr}$ and 100% efficiency assuming ${\sin }^2\left(2\mathrm{}\theta \right)=0.863\mathrm{}$ and $\delta m^2=7.3\mathrm{}\times {10}^{-5}{\mathrm{eV}}^2.$ The maximal prediction is 55 events, obtained in a model with fully radiogenic production of the terrestrial heat flow.