We introduce a simulation framework for the transport of high and low energy electrons in xenon-based optical time projection chambers (OTPCs). The simulation relies on elementary cross sections ...(electron–atom and electron–molecule) and incorporates, in order to compute the gas scintillation, the reaction/quenching rates (atom–atom and atom–molecule) of the first 41 excited states of xenon and the relevant associated excimers, together with their radiative cascade. The results compare positively with observations made in pure xenon and its mixtures with CO2 and CF4 in a range of pressures from 0.1 to 10 bar. This work sheds some light on the elementary processes responsible for the primary and secondary xenon-scintillation mechanisms in the presence of additives, that are of interest to the OTPC technology.
The amount of sensitive data stored on electronic media increases as the use of computers and mobile devices becomes more prevalent. For example, home computers and devices may store financial ...information (e.g., Quicken files or tax documents), usernames and passwords, private correspondence (e.g., emails or chat logs), and personal media files (e.g., pictures or videos). Business computers and devices may store sensitive client data and trade secrets. Government computers and devices may store personally identifiable data on citizens and various classified materials. As the amount of digital sensitive information accrues, the need for the ability to securely remove this information increases. Short of physically destroying the entire storage medium, existing secure-deletion solutions tend to be piecemeal at best – they may only work for one type of storage or file system, may force the user to delete all files instead of selective files, may require the added complexities of encryption and key storage, may require extensive changes and additions to the computer's operating system or storage firmware, and may not handle system crashes gracefully. This dissertation introduces TrueErase, a holistic secure-deletion framework that irrevocably deletes data and metadata. At heart, TrueErase is an information-propagation framework that works alongside of legacy operating system components for easier integration. Through its design, implementation, verification, and evaluation on both a hard drive and emerging solid-state storage, TrueErase shows that it is possible to construct a holistic, per-file, encryption-free, secure-deletion framework that accommodates different storage media and legacy file systems, requires limited changes to legacy systems, and handles common crash scenarios. The experience of building TrueErase further contributes insight into the mechanisms and complexities of the legacy operating system storage data path.
We present evidence of non-excimer-based secondary scintillation in gaseous xenon, obtained using both the NEXT-White 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 has been postulated to exist in xenon that has been largely overlooked. For photon emission below 1000 nm, the NBrS yield increases from about 10\(^{-2}\) photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\) at pressure-reduced electric field values of 50 V cm\(^{-1}\) bar\(^{-1}\) to above 3\(\times\)10\(^{-1}\) photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\) at 500 V cm\(^{-1}\) bar\(^{-1}\). Above 1.5 kV cm\(^{-1}\) bar\(^{-1}\), values that are typically employed for electroluminescence, it is estimated that NBrS is present with an intensity around 1 photon/e\(^{-}\) cm\(^{-1}\) bar\(^{-1}\), which is about two 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" and "veto" regions, where keeping the electric field below the electroluminescence (EL) threshold will not suffice to extinguish secondary scintillation. The electric field in these regions should be chosen carefully to avoid intolerable levels of NBrS emission. Furthermore, we show that this new source of light emission opens up a viable path towards obtaining S2 signals for discrimination purposes in future single-phase liquid TPCs for neutrino and dark matter physics, with estimated yields up to 20-50 photons/e\(^{-}\) cm\(^{-1}\).
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 (\(2\nu ECEC\)) 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, \(0\nu ECEC\). Here we report on the current sensitivity of the NEXT-White detector to \(^{124}\)Xe \(2\nu ECEC\) and on the extrapolation to NEXT-100. Using simulated data for the \(2\nu ECEC\) 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 \(2\nu ECEC\) half-life of \(6 \times 10^{22}\) y (at 90% confidence level) or better can be reached.
Convolutional neural networks (CNNs) are widely used state-of-the-art computer vision tools that are becoming increasingly popular in high energy physics. In this paper, we attempt to understand the ...potential of CNNs for event classification in the NEXT experiment, which will search for neutrinoless double-beta decay in \(^{136}\)Xe. To do so, we demonstrate the usage of CNNs for the identification of electron-positron pair production events, which exhibit a topology similar to that of a neutrinoless double-beta decay event. These events were produced in the NEXT-White high-pressure xenon TPC using 2.6-MeV gamma rays from a \(^{228}\)Th calibration source. We train a network on Monte Carlo-simulated events and show that, by applying on-the-fly data augmentation, the network can be made robust against differences between simulation and data. The use of CNNs offer significant improvement in signal efficiency/background rejection when compared to previous non-CNN-based analyses.
We examine properties of $t\overline{t}$ candidate events in lepton + jets final states to establish the helicities of W bosons in $t\rightarrow$W+b$ decays. Our analysis is based on a direct ...calculation of a probability density for each event to correspond to a $t\overline{t}$ final state, as a function of the helicity of the $W$ boson. Using the 125 events/pb of data collected by the D0 experiment at the Fermilab Tevatron $p\overline{p}$ Collider at $\sqrt{s}$=1.8 TeV, we obtain a longitudinal helicity fraction $F_0$=0.56$\pm$0.31, consistent with the prediction of $F_0$=0.70 from the standard model.
Polytetrafluoroethylene (PTFE) is an excellent diffuse reflector widely used in light collection systems for particle physics experiments. However, the reflectance of PTFE is a function of its ...thickness. In this work, we investigate this dependence in air for light of wavelengths 260 nm and 450 nm using two complementary methods. We find that PTFE reflectance for thicknesses from 5 mm to 10 mm ranges from 92.5% to 94.5% at 450 nm, and from 90.0% to 92.0% at 260 nm. We also see that the reflectance of PTFE of a given thickness can vary by as much as 2.7% within the same piece of material. Finally, we show that placing a specular reflector behind the PTFE can recover the loss of reflectance in the visible without introducing a specular component in the reflectance.
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