ABSTRACT
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 (12 306±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}.
ABSTRACT
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 (12 306±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 σ[over ¯]_{e}, the axioelectric coupling constant g_{Ae}, and the dark photon kinetic mixing parameter κ. We also set the first dark matter direct-detection constraints on the mixing angle |U_{e4}|^{2} for keV/c^{2} sterile neutrinos.
ABSTRACT
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 MeV/c^{2}.
ABSTRACT
We present the results of a search for dark matter weakly interacting massive particles (WIMPs) in the mass range below 20 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 keVee. The observed rate in the detector at 0.5 keVee is about 1.5 event/keVee/kg/d and is almost entirely accounted for by known background sources. We obtain a 90% C.L. exclusion limit above 1.8 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 GeV/c^{2}.
ABSTRACT
E-cadherin and ß-catenin have been studied in carcinogenesis and tumour progression and reduced membrane expression of these molecules in canine mammary tumours has been associated with a poor prognosis. The present study investigated immunohistochemically the expression of E-cadherin and ß-catenin in 53 mammary tumours and 48 hyperplastic or dysplastic lesions from 57 queens. E-cadherin and ß-catenin expression was membranous in all samples and there was a significant decrease in expression in malignant tumours and metastases. Cytoplasmic expression of both markers was inversely correlated to the membrane localization. ß-catenin nuclear labelling was detected in one lymph node metastasis (60% positive cells) and in the basal/myoepithelial cells of 6/7 ductal tumours. No correlation with survival was found for either marker. These results confirm the role of these proteins in maintaining tissue architecture and in inhibiting cell invasiveness and potentially indicate the oncogenic potential of the Wnt/ß-catenin transduction pathway in feline mammary tumours. In addition, specific independent expression of ß-catenin in the nuclei of basal/myoepithelial cells might suggest that this molecule is involved in regulation of the mammary stem/pluripotent cell component. Further studies should include more cases of benign mammary neoplasia and further investigate ß-catenin nuclear expression in ductal tumours.
