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The imaging of individual Ba 2+ ions in high pressure xenon gas is one possible way to attain background-free sensitivity to neutrinoless double beta decay and hence establish the Majorana nature of the neutrino. In this paper we demonstrate selective single Ba 2+ ion imaging inside a high-pressure xenon gas environment. Ba 2+ ions chelated with molecular chemosensors are resolved at the gas-solid interface using a diffraction-limited imaging system with scan area of 1 × 1 cm 2 located inside 10 bar of xenon gas. This form of microscopy represents key ingredient in the development of barium tagging for neutrinoless double beta decay searches in 136 Xe. This also provides a new tool for studying the photophysics of fluorescent molecules and chemosensors at the solid-gas interface to enable bottom-up design of catalysts and sensors. Barium tagging is a key ingredient for future detectors of neutrinoless double beta decay in low-background environments. Here, the authors demonstrate fluorescence imaging of single Ba2+ ions in high pressure Xenon gas, by comparing activity between Ba2+ chelated and unchelated samples of crown-ether chemosensors.

The imaging of individual Ba2+ ions in high pressure xenon gas is one possible way to attain background-free sensitivity to neutrinoless double beta decay and hence establish the Majorana nature of the neutrino. In this paper we demonstrate selective single Ba2+ ion imaging inside a high-pressure xenon gas environment. Ba2+ ions chelated with molecular chemosensors are resolved at the gas-solid interface using a diffraction-limited imaging system with scan area of 1 × 1 cm2 located inside 10 bar of xenon gas. This form of microscopy represents key ingredient in the development of barium tagging for neutrinoless double beta decay searches in 136Xe. This also provides a new tool for studying the photophysics of fluorescent molecules and chemosensors at the solid-gas interface to enable bottom-up design of catalysts and sensors.

We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White time projection chamber (TPC) and a dedicated setup. Detailed comparison with first-principle calculations allows us to assign this scintillation mechanism to neutral bremsstrahlung (NBrS), a process that is postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about10−2photon/e−cm−1bar−1at pressure-reduced electric field values of50Vcm−1bar−1to above3×10−1photon/e−cm−1bar−1at500Vcm−1bar−1. Above1.5kVcm−1bar−1, values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around1photon/e−cm−1bar−1, which is about 2 orders of magnitude lower than conventional, excimer-based electroluminescence. Despite being fainter than its excimeric counterpart, our calculations reveal that NBrS causes luminous backgrounds that can interfere, in either gas or liquid phase, with the ability to distinguish and/or to precisely measure low primary-scintillation signals (S1). In particular, we show this to be the case in the “buffer” region, where keeping the electric field below the electroluminescence threshold does not suffice to extinguish secondary scintillation. The electric field leakage in this region should be mitigated to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path toward obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to20–50photons/e−cm−1.

A bstract Double electron capture by proton-rich nuclei is a second-order nuclear process analogous to double beta decay. Despite their similarities, the decay signature is quite different, potentially providing a new channel to measure the hypothesized neutrinoless mode of these decays. The Standard-Model-allowed two-neutrino double electron capture (2 νEC EC ) has been predicted for a number of isotopes, but only observed in 78 Kr, 130 Ba and, recently, 124 Xe. The sensitivity to this decay establishes a benchmark for the ultimate experimental goal, namely the potential to discover also the lepton-number-violating neutrinoless version of this process, 0 νEC EC . Here we report on the current sensitivity of the NEXT-White detector to 124 Xe 2 νEC EC and on the extrapolation to NEXT-100. Using simulated data for the 2 νEC EC signal and real data from NEXT-White operated with 124 Xe-depleted gas as background, we define an optimal event selection that maximizes the NEXT-White sensitivity. We estimate that, for NEXT-100 operated with xenon gas isotopically enriched with 1 kg of 124 Xe and for a 5-year run, a sensitivity to the 2 νEC EC half-life of 6 × 10 22 y (at 90% confidence level) or better can be reached.

We present a tunable metal ion beam that delivers controllable ion currents in the picoamp range for testing of dry-phase ion sensors. Ion beams are formed by sequential atomic evaporation and single or multiple electron impact ionization, followed by acceleration into a sensing region. Controllability of the ionic charge state is achieved through tuning of electrode potentials that influence the retention time in the ionization region. Barium, lead, and cobalt samples have been used to test the system, with ion currents identified and quantified using a quadrupole mass analyzer. Realization of a clean \\(Ba^2+\\) ion beam within a bench-top system represents an important technical advance toward the development and characterization of barium tagging systems for neutrinoless double beta decay searches in xenon gas. This system also provides a testbed for investigation of novel ion sensing methodologies for environmental assay applications, with dication beams of Pb\\(^2+\\) and Cd\\(^2+\\) also demonstrated for this purpose.

We report a measurement of the half-life of the \\({}^{136}\\)Xe two-neutrino double beta decay performed with a novel direct background subtraction technique. The analysis relies on the data collected with the NEXT-White detector operated with \\({}^{136}\\)Xe-enriched and \\({}^{136}\\)Xe-depleted xenon, as well as on the topology of double-electron tracks. With a fiducial mass of only 3.5 kg of Xe, a half-life of \\(2.34^{+0.80}_{-0.46}\\textrm{(stat)}^{+0.30}_{-0.17}\\textrm{(sys)}\\times10^{21}~\\textrm{yr}\\) is derived from the background-subtracted energy spectrum. The presented technique demonstrates the feasibility of unique background-model-independent neutrinoless double beta decay searches.

If neutrinos are their own antiparticles, the otherwise-forbidden nuclear reaction known as neutrinoless double beta decay (\\(\\beta\\beta 0\\nu\\)) can occur, with a characteristic lifetime which is expected to be very long, making the suppression of backgrounds a daunting task. It has been shown that detecting (``tagging'') the Ba\\(^{+2}\\) dication produced in the double beta decay \\({}^{136}\\mathrm{Xe} \\rightarrow {}^{136}\\)Ba\\(^{+2}+ 2 e + (2 \\nu)\\) in a high pressure gas experiment, could lead to a virtually background free experiment. To identify these \\Bapp, chemical sensors are being explored as a key tool by the NEXT collaboration . Although used in many fields, the application of such chemosensors to the field of particle physics is totally novel and requires experimental demonstration of their suitability in the ultra-dry environment of a xenon gas chamber. Here we use a combination of complementary surface science techniques to unambiguously show that Ba\\(^{+2}\\) ions can be trapped (chelated) in vacuum by an organic molecule, the so-called fluorescent bicolour indicator (FBI) (one of the chemosensors developed by NEXT), immobilized on a surface. We unravel the ion capture mechanism once the molecules are immobilised on Au(111) surface and explain the origin of the emission fluorescence shift associated to the trapping of different ions. Moreover, we prove that chelation also takes place on a technologically relevant substrate, as such, demonstrating the feasibility of using FBI indicators as building blocks of a Ba\\(^{+2}\\) detector.

Radio-frequency (RF) carpets with ultra-fine pitches are examined for ion transport in gases at atmospheric pressures and above. We develop new analytic and computational methods for modeling RF ion transport at densities where dynamics are strongly influenced by buffer gas collisions. An analytic description of levitating and sweeping forces from phased arrays is obtained, then thermodynamic and kinetic principles are used to calculate ion loss rates in the presence of collisions. This methodology is validated against detailed microscopic SIMION simulations. We then explore a parameter space of special interest for neutrinoless double beta decay experiments: transport of barium ions in xenon at pressures from 1 to 10 bar. Our computations account for molecular ion formation and pressure dependent mobility as well as finite temperature effects. We discuss the challenges associated with achieving suitable operating conditions, which lie beyond the capabilities of existing devices, using presently available or near-future manufacturing techniques.

\\Xe{136} is used as the target medium for many experiments searching for \\bbnonu. Despite underground operation, cosmic muons that reach the laboratory can produce spallation neutrons causing activation of detector materials. A potential background that is difficult to veto using muon tagging comes in the form of \\Xe{137} created by the capture of neutrons on \\Xe{136}. This isotope decays via beta decay with a half-life of 3.8 minutes and a \\Qb\\ of \\(\\sim\\)4.16 MeV. This work proposes and explores the concept of adding a small percentage of \\He{3} to xenon as a means to capture thermal neutrons and reduce the number of activations in the detector volume. When using this technique we find the contamination from \\Xe{137} activation can be reduced to negligible levels in tonne and multi-tonne scale high pressure gas xenon neutrinoless double beta decay experiments running at any depth in an underground laboratory.

Cytoplasmic dynein 1 is an important microtubule-based motor in many eukaryotic cells. Dynein has critical roles both in interphase and during cell division. Here, we focus on interphase cargoes of dynein, which include membrane-bound organelles, RNAs, protein complexes and viruses. A central challenge in the field is to understand how a single motor can transport such a diverse array of cargoes and how this process is regulated. The molecular basis by which each cargo is linked to dynein and its cofactor dynactin has started to emerge. Of particular importance for this process is a set of coiled-coil proteins — activating adaptors — that both recruit dynein–dynactin to their cargoes and activate dynein motility.