Dark matter induced event rate in an Earth-based detector is predicted to show an annual modulation as a result of the Earth's orbital motion around the Sun. We searched for this modulation signature ...using the ionization signal of the DarkSide-50 liquid argon time projection chamber. No significant signature compatible with dark matter is observed in the electron recoil equivalent energy range above \(40~{\rm eV_{ee}}\), the lowest threshold ever achieved in such a search.
We present a novel approach for the search of dark matter in the DarkSide-50 experiment, relying on Bayesian Networks. This method incorporates the detector response model into the likelihood ...function, explicitly maintaining the connection with the quantity of interest. No assumptions about the linearity of the problem or the shape of the probability distribution functions are required, and there is no need to morph signal and background spectra as a function of nuisance parameters. By expressing the problem in terms of Bayesian Networks, we have developed an inference algorithm based on a Markov Chain Monte Carlo to calculate the posterior probability. A clever description of the detector response model in terms of parametric matrices allows us to study the impact of systematic variations of any parameter on the final results. Our approach not only provides the desired information on the parameter of interest, but also potential constraints on the response model. Our results are consistent with recent published analyses and further refine the parameters of the detector response model.
We report on the search for dark matter WIMPs in the mass range below 10 GeV/c\(^2\), from the analysis of the entire dataset acquired with a low-radioactivity argon target by the DarkSide-50 ...experiment at LNGS. The new analysis benefits from more accurate calibration of the detector response, improved background model, and better determination of systematic uncertainties, allowing us to accurately model the background rate and spectra down to 0.06 keV\(_{er}\). A 90% C.L. exclusion limit for the spin-independent cross section of 3 GeV/c\(^2\) mass WIMP on nucleons is set at 6\(\times\)10\(^{-43}\) cm\(^2\), about a factor 10 better than the previous DarkSide-50 limit. This analysis extends the exclusion region for spin-independent dark matter interactions below the current experimental constraints in the \(1.2, 3.6\) GeV/c\(^2\) WIMP mass range.
We present a search for dark matter particles with sub-GeV/\(c^2\) masses whose interactions have final state electrons using the DarkSide-50 experiment's (12306 \(\pm\) 184) kg d low-radioactivity ...liquid argon exposure. By analyzing the ionization signals, we exclude new parameter space for the dark matter-electron cross section \(\bar{\sigma}_e\), the axioelectric coupling constant \(g_{Ae}\), and the dark photon kinetic mixing parameter \(\kappa\). We also set the first dark matter direct-detection constraints on the mixing angle \(\left|U_{e4}\right|^2\) for keV sterile neutrinos.
Dark matter elastic scattering off nuclei can result in the excitation and ionization of the recoiling atom through the so-called Migdal effect. The energy deposition from the ionization electron ...adds to the energy deposited by the recoiling nuclear system and allows for the detection of interactions of sub-GeV/c\(^2\) mass dark matter. We present new constraints for sub-GeV/c\(^2\) dark matter using the dual-phase liquid argon time projection chamber of the DarkSide-50 experiment with an exposure of (12306 \(\pm\) 184) kg d. The analysis is based on the ionization signal alone and significantly enhances the sensitivity of DarkSide-50, enabling sensitivity to dark matter with masses down to 40 MeV/c\(^2\). Furthermore, it sets the most stringent upper limit on the spin independent dark matter nucleon cross section for masses below \(3.6\) GeV/c\(^2\).
Finding unequivocal evidence of dark matter interactions in a particle detector is a major objective of physics research. Liquid argon time projection chambers offer a path to probe Weakly ...Interacting Massive Particles scattering cross sections on nucleus down to the so-called neutrino floor, in a mass range from few GeV's to hundredths of TeV's. Based on the successful operation of the DarkSide-50 detector at LNGS, a new and more sensitive experiment, DarkSide-20k, has been designed and is now under construction. A thorough understanding of the DarkSide-50 detector response and, therefore, of all kind of observed events, is essential for an optimal design of the new experiment. In this paper, we report on a particular set of events, which were not used for dark matter searches. Namely, standard two-pulse scintillation-ionization signals accompanied by a small amplitude third pulse, originating from single or few electrons, in a time window of less than a maximum drift time. We compare our findings to those of a recent paper of the LUX Collaboration (D.S.Akerib et al. Phys.Rev.D 102, 092004). Indeed, both experiments observe events related to photoionization of the cathode. From the measured rate of these events, we estimate for the first time the quantum efficiency of the tetraphenyl butadiene deposited on the DarkSide-50 cathode at wavelengths around 128 nm, in liquid argon. Also, both experiments observe events likely related to photoionization of impurities in the liquid. The probability of photoelectron emission per unit length turns out to be one order of magnitude smaller in DarkSide-50 than in LUX. This result, together with the much larger measured electron lifetime, coherently hints toward a lower concentration of contaminants in DarkSide-50 than in LUX.
DarkSide-50 has demonstrated the high potential of dual-phase liquid argon time projection chambers in exploring interactions of WIMPs in the GeV/c\(^2\) mass range. The technique, based on the ...detection of the ionization signal amplified via electroluminescence in the gas phase, allows to explore recoil energies down to the sub-keV range. We report here on the DarkSide-50 measurement of the ionization yield of electronic recoils down to \(\sim\)180~eV\(_{er}\), exploiting \(^{37}\)Ar and \(^{39}\)Ar decays, and extrapolated to a few ionization electrons with the Thomas-Imel box model. Moreover, we present a model-dependent determination of the ionization response to nuclear recoils down to \(\sim\)500~eV\(_{nr}\), the lowest ever achieved in liquid argon, using \textit{in situ} neutron calibration sources and external datasets from neutron beam experiments.
We reanalize data collected with the DarkSide-50 experiment and recently used to set limits on the spin-independent interaction rate of weakly interacting massive particles (WIMPs) on argon nuclei ...with an effective field theory framework. The dataset corresponds to a total (16660 \(\pm\) 270) kg d exposure using a target of low-radioactivity argon extracted from underground sources. We obtain upper limits on the effective couplings of the 12 leading operators in the nonrelativistic systematic expansion. For each effective coupling we set constraints on WIMP-nucleon cross sections, setting upper limits between \(2.4 \times 10^{-45} \, \mathrm{cm}^2\) and \(2.3 \times 10^{-42} \, \mathrm{cm}^2\) (8.9 \(\times 10^{-45} \, \mathrm{cm}^2\) and 6.0 \(\times 10^{-42} \, \mathrm{cm}^2\)) for WIMPs of mass of 100 \(\mathrm{GeV/c^2}\) (1000 \(\mathrm{GeV/c^2}\)) at 90\% confidence level.
We report measurements of the charged daughter fraction of \(^{218}\)Po as a result of the \(^{222}\)Rn alpha decay, and the mobility of \(^{218}\)Po\(^+\) ions, using radon-polonium coincidences ...from the \(^{238}\)U chain identified in 532 live-days of DarkSide-50 WIMP-search data. The fraction of \(^{218}\)Po that is charged is found to be 0.37\(\pm\)0.03 and the mobility of \(^{218}\)Po\(^+\) is (8.6\(\pm\)0.1)\(\times\)10$^{-4}$$\frac{\text{cm}^2}{\text{Vs}}$.
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 ...(16,660+-270) kg 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 1.14E-44 cm^2 (3.78E-44 cm^2, 3.43E-43 cm^2) for a WIMP mass of 100 GeV/c^2 (1 TeV/c^2, 10 TeV/c^2).
