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.
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 examined how different facets of guira cuckoo sociality influence reproductive investment in eggs (mass, volume, albumen, yolk, shell weight and thickness). The highly variable egg size in this ...species suggests the possibility of reproductive manipulation by females. Our data support the hypothesis that investment in eggs and clutches reflects a social context. The lowest egg ejection probabilities occurred in very small communal clutches where there were fewer laying females. Eggs retained in the nest had larger yolks than those ejected, a possible mechanism for minimizing energy expenditure in eggs with high chances of failure. Results showed that eggs laid in smaller communal clutches had, on average, less investment in all nutrient measures, except yolk, compared with eggs from larger communal clutches. It may be important for eggs to be of high quality in larger communal clutches, where competition between hatchlings will most likely be intense. Larger guira cuckoo eggs in this study produced heavier chicks. We found that chicks that were smaller and lighter at hatching were victimized by infanticide significantly more than chicks that were heavier and bigger at hatching.
Guira cuckoos, Guira guira, exhibit a rare polygynandrous reproductive system with groups containing several male and female breeders, allowing for important tests of reproductive skew models. Female ...reproductive strategies involve leaving the group, varying clutch size, egg ejection and infanticide, among others. Here we examined the predictions of reproductive skew models relative to reproductive partitioning among females in groups. We used yolk protein electrophoresis to identify individual females’ eggs in joint nests. We found that reproductive partitioning favors early-laying females, which lay and incubate more eggs than females that begin laying later. Because the female that lays first tends to switch between repeated nesting bouts, and females do not always contribute eggs to each bout, female reproductive success tends to equalize within groups over time. The pattern of reproductive partitioning differs from that described for anis, another crotophagine joint-nester. We calculated reproductive skew indices for groups in 2 years, for both laying and incubation, as well as an overall population value. These were compared to random skew generated by simulations. Varying degrees of skew were found for different groups, and also across sequential nesting bouts of the same groups. Overall, however, skew did not deviate from random within the population. Nests that reached incubation tended to have lower skew values during the laying phase than nests terminated due to ejection of all eggs followed by desertion. Groups had higher reproductive skew indices in their first nesting bout of the season, and these nests frequently failed. These results illustrate the importance of social organization in determining not only individual, but group success in reproduction, and highlight the flexibility of vertebrate social behavior.
Egg characteristics have been used to determine egg maternity for birds in situations where two or more females lay eggs in a single nest (as in communal breeders and intraspecific parasites). We ...assessed the applicability of egg morphometry and eggshell appearance in ascribing egg ownership in communal clutches of guira cuckoos Guira guira, a species where up to seven females may lay eggs in a joint nest. We used both combined variables (including egg mass, length, width, shape and two eggshell variables), and a shape index to test whether eggs laid by each female were similar but different from eggs laid by other females. Also, we conducted discriminant function analyses to verify if eggs could be correctly classified to their mothers based on their characteristics. The correct maternity was determined by yolk protein electrophoresis of freshly-laid eggs. Individual female chutches were separated through egg characteristics or shape alone in 29% and 41% of the groups tested, respectively. Differences were mostly due to a single female that differed from her nest-mates in a unique egg variable. On average, 55% of the eggs analyzed were not assigned to the correct mother using egg dimensions and eggshell speckling pattern. In conclusion, the egg characteristics used do not reliably indicate maternity in guira cuckoo communal clutches. We therefore recommend a protein-based verification of egg appearance characteristics for assigning maternity in other species in which multiple female laying occurs.
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.
A double-phase argon Time Projection Chamber (TPC), with an active mass of 185 g, has been designed and constructed for the Recoil Directionality (ReD) experiment. The aim of the ReD project is to ...investigate the directional sensitivity of argon-based TPCs via columnar recombination to nuclear recoils in the energy range of interest (20-200 keV\(_{nr}\)) for direct dark matter searches. The key novel feature of the ReD TPC is a readout system based on cryogenic Silicon Photomultipliers, which are employed and operated continuously for the first time in an argon TPC. Over the course of six months, the ReD TPC was commissioned and characterised under various operating conditions using \(\gamma\)-ray and neutron sources, demonstrating remarkable stability of the optical sensors and reproducibility of the results. The scintillation gain and ionisation amplification of the TPC were measured to be \(g_1 = (0.194 \pm 0.013)\) PE/photon and \(g_2 = (20.0 \pm 0.9)\) PE/electron, respectively. The ratio of the ionisation to scintillation signals (S2/S1), instrumental for the positive identification of a candidate directional signal induced by WIMPs, has been investigated for both nuclear and electron recoils. At a drift field of 183 V/cm, an S2/S1 dispersion of 12% was measured for nuclear recoils of approximately 60-90 keV\(_{nr}\), as compared to 18% for electron recoils depositing 60 keV of energy. The detector performance reported here meets the requirements needed to achieve the principal scientific goals of the ReD experiment in the search for a directional effect due to columnar recombination. A phenomenological parameterisation of the recombination probability in LAr is presented and employed for modeling the dependence of scintillation quenching and charge yield on the drift field for electron recoils between 50-500 keV and fields up to 1000 V/cm.
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.
