The challenges of measuring plastic pollution

Plastic is a single word for a multifaceted reality, encompassing a wide variety of polymers and additives with different chemical and physical properties. The end products range from single-use plastic bags, food wraps and plastic bottles, to fishing lines, buoys, and synthetic fibres used in the clothing or fishing industries.As the use of plastic is pervasive, so is plastic pollution. An estimated 10 million tonnes of plastic leaks into the ocean each year, causing an unprecedented environmental crisis. Measuring or forecasting this issue is a complex and challenging task, due to technical limitations and uncoordinated assessment campaigns. Acting to tackle this issue requires adequate metrics to guide and prioritise action at different levels, ranging from sound product design and efficient regional infrastructure, to adequate policies and enforcement

Détection directionnelle de matière sombre avec MIMAC

De nombreuses mesures cosmologiques et astrophysiques tendent à montrer que notre galaxie serait englobée par un halo de matière sombre non-baryonique. La détection directionnelle vise à mesurer la direction du recul nucléaire issu d'une interaction avec une particule de matière sombre. Cela permettrait de mettre en évidence la forte dépendance angulaire de la distribution de reculs due à la rotation du système solaire autour du centre galactique. Cette thèse aborde la détection directionnelle par une approche multi-thématique : phénoménologie, expérimentale et analyse de données. L'objectif des études phénoménologiques est de montrer l'apport d'un détecteur directionnel en terme de recherche de matière sombre. Grâce au développement de méthodes statistiques dédiées, on montre qu'un détecteur tel que celui proposé par la collaboration MIMAC, devrait permettre de découvrir la matière sombre avec une grande significance jusqu'à des sections efficaces 2 à 3 ordres de grandeur en dessous des limites actuelles. La mise en place d'une méthodologie d'analyse de données directionnelles constitue un second objectif de cette thèse car la reconstruction 3D des traces mesurées est un point clef de cette nouvelle stratégie de détection. On présente ainsi une nouvelle méthode d'analyse basée sur une approche par vraisemblance, permettant d'optimiser l'estimation des paramètres de chaque événement mesuré: position dans le détecteur et direction. Dans le cadre de la discrimination du bruit de fond électronique, on a mis en place une étude basée sur la topologie de la trace et utilisant une analyse par arbres de décision boostés qui nous permet d'obtenir des facteurs de rejet environ 20 fois supérieurs à ceux obtenus avec des analyses séquentielles. Du point de vue expérimental, on présente une méthode originale de la mesure de vitesse de dérive des électrons permettant d'obtenir des incertitudes de l'ordre du pourcent et de contraindre simultanément les coefficients de diffusion longitudinale. On termine enfin sur l'analyse des données obtenues auprès du champ de neutrons AMANDE permettant de valider la stratégie de détection du projet MIMAC.A large number of cosmological and astrophysical measurements supports the fact that our galaxy should be immersed in a halo of non-baryonic dark matter. Directional detection aims at measuring the direction of recoiling nucleus following an elastic scattering with a Dark Matter particle. This should allow us to show the expected strong angular dependence of the recoil distribution due to the rotation of the Solar System around the galactic center. This thesis presents a comprehensive study of directional detection following three different aspects: phenomenology, experimental and data analysis. The goal of the phenomenological studies is to explore the interest of directional detection in terms of galactic dark matter search. With the use of dedicated statistical tools we show that a detector, as the one proposed by the MIMAC collaboration, should be able to discover dark matter with a high significance down to cross sections 2 to 3 orders of magnitude below current limits. Setting up a new strategy of data analysis is a second goal of this thesis as an efficient 3D track reconstruction is compulsory to achieve an accurate directional detection of dark matter. We present a new method based on a likelihood approach aiming at the optimisation of the estimation of the parameters of each measured track: position in the detector volume and direction. In the context of reducing the electronic background, we present a method based on the analysis of the track topology using a boosted decision tree algorithm which enhances the rejection power by a factor 20 with respect to a sequential analysis. In the context of experimental measurement, we present a new method dedicated to the measurement of the electron drift velocity with uncertainties of the order of the percent and constraining the longitudinal diffusion coefficients. Eventually, we discuss the results of a data analysis obtained during an acquisition using a neutron field which validate the detection strategy of the MIMAC experiment.SAVOIE-SCD - Bib.électronique (730659901) / SudocGRENOBLE1/INP-Bib.électronique (384210012) / SudocGRENOBLE2/3-Bib.électronique (384219901) / SudocSudocFranceF

Correlation between structural and optical properties of WO3 thin films sputter deposited by glancing angle deposition

International audienceTungsten oxide WO3 thin films are prepared by DC reactive sputtering. The GLancing Angle Deposition method (GLAD) is implemented to produce inclined columnar structures. The incident angle α between the particle flux and the normal to the substrate is systematically changed from 0 to 80°. For incident angles higher than 50°, a typical inclined columnar architecture is clearly produced with column angles β well correlated with the incident angle α according to conventional relationships determined from geometrical models. For each film, the refractive index and extinction coefficient are calculated from optical transmittance spectra of the films measured in the visible region. The refractive index at 589 nm drops from n589 = 2.18 down to 1.90 as α rises from 0 to 80°, whereas the extinction coefficient reaches k589 = 4.27 × 10−3 for an incident angle α = 80°, which indicates that the films produced at a grazing incident angle become more absorbent. Such changes of the optical behaviors are correlated with changes of the microstructure, especially a porous architecture, which is favored for incident angles higher than 50°. Optical band gap Eg, Urbach energy Eu and birefringence Δn617, determined from optical transmittance measurements, are also influenced by the orientation of the columns and their trend is discussed taking into account the disorder produced by the inclined particle flux

Readout strategies for directional dark matter detection beyond the neutrino background

The search for weakly interacting massive particles (WIMPs) by direct detection faces an en- croaching background due to coherent neutrino-nucleus scattering. As the sensitivity of these ex- periments improves, the question of how to best distinguish a dark matter signal from neutrinos will become increasingly important. A proposed method of overcoming this so-called “neutrino floor” is to utilize the directional signature that both neutrino and dark matter induced recoils possess. We show that directional experiments can indeed probe WIMP-nucleon cross-sections below the neutrino floor with little loss in sensitivity due to the neutrino background. In particular we find at low WIMP masses (around 6 GeV) the discovery limits for directional detectors penetrate be- low the non-directional limit by several orders of magnitude. For high WIMP masses (around 100 GeV), the non-directional limit is overcome by a factor of a few. Furthermore we show that even for directional detectors which can only measure 1- or 2-dimensional projections of the 3-dimensional recoil track, the discovery potential is only reduced by a factor of 3 at most. We also demonstrate that while the experimental limitations of directional detectors, such as sense recognition and finite angular resolution, have a detrimental effect on the discovery limits, it is still possible to overcome the ultimate neutrino background faced by non-directional detectors

Characterization of the phonon sensor of the CRYOSEL detector with IR photons

The sensitivities of light Dark Matter (DM) particle searches with cryogenic detectors are mostly limited by large backgrounds of events that do not produce ionization signal. The CRYOSEL project develops a new technique where this background in a germanium cryogenic detector is rejected by using the signals from a Superconducting Single Electron Device (SSED) sensor designed to detect the phonons emitted through the Neganov-Trofimov-Luke effect by the e$^-$h$^+$ pairs as they drift in a close-by very high-field region. A tag on signals from this device should suppress the heat-only background. The measurement of the response to IR laser pulses of the first CRYOSEL prototype show the relevance of such sensor technology.Comment: 9 pages, 3 figures, LTD2

Dark matter effective field theory scattering in direct detection experiments

We examine the consequences of the effective field theory (EFT) of dark matter–nucleon scattering for current and proposed direct detection experiments. Exclusion limits on EFT coupling constants computed using the optimum interval method are presented for SuperCDMS Soudan, CDMS II, and LUX, and the necessity of combining results from multiple experiments in order to determine dark matter parameters is discussed. We demonstrate that spectral differences between the standard dark matter model and a general EFT interaction can produce a bias when calculating exclusion limits and when developing signal models for likelihood and machine learning techniques. We also discuss the implications of the EFT for the next-generation (G2) direct detection experiments and point out regions of complementarity in the EFT parameter space.National Science Foundation (U.S.)United States. Dept. of EnergyNatural Sciences and Engineering Research Council of CanadaSpain. Ministerio de Economia y Competitividad (MultiDark

Improved WIMP-search reach of the CDMS II germanium data

CDMS II data from the five-tower runs at the Soudan Underground Laboratory were reprocessed with an improved charge-pulse fitting algorithm. Two new analysis techniques to reject surface-event backgrounds were applied to the 612 kg days germanium-detector weakly interacting massive particle (WIMP)-search exposure. An extended analysis was also completed by decreasing the 10 keV analysis threshold to ~5  keV, to increase sensitivity near a WIMP mass of 8  GeV/c[superscript 2]. After unblinding, there were zero candidate events above a deposited energy of 10 keV and six events in the lower-threshold analysis. This yielded minimum WIMP-nucleon spin-independent scattering cross-section limits of 1.8 × 10[superscript −44] and 1.18 × 10[superscript −41] at 90% confidence for 60 and 8.6  GeV/c[superscript 2] WIMPs, respectively. This improves the previous CDMS II result by a factor of 2.4 (2.7) for 60 (8.6)  GeV/c[superscript 2] WIMPs.National Science Foundation (U.S.)United States. Dept. of EnergyNatural Sciences and Engineering Research Council of CanadaSpain. Ministerio de Economia y Competitividad (MultiDark

New Results from the Search for Low-Mass Weakly Interacting Massive Particles with the CDMS Low Ionization Threshold Experiment

The CDMS low ionization threshold experiment (CDMSlite) uses cryogenic germanium detectors operated at a relatively high bias voltage to amplify the phonon signal in the search for weakly interacting massive particles (WIMPs). Results are presented from the second CDMSlite run with an exposure of 70 kg day, which reached an energy threshold for electron recoils as low as 56 eV. A fiducialization cut reduces backgrounds below those previously reported by CDMSlite. New parameter space for the WIMP-nucleon spin-independent cross section is excluded for WIMP masses between 1.6 and 5.5  GeV/c[superscript 2].National Science Foundation (U.S.)United States. Dept. of EnergyFermi National Accelerator Laboratory (Visiting Scholar Award 13-S-04

Searching for Low-Mass Dark Matter with Cryogenic Detectors

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