54 research outputs found

    Observation of the effect of gravity on the motion of antimatter

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    Einstein’s general theory of relativity from 19151 remains the most successful description of gravitation. From the 1919 solar eclipse2 to the observation of gravitational waves3, the theory has passed many crucial experimental tests. However, the evolving concepts of dark matter and dark energy illustrate that there is much to be learned about the gravitating content of the universe. Singularities in the general theory of relativity and the lack of a quantum theory of gravity suggest that our picture is incomplete. It is thus prudent to explore gravity in exotic physical systems. Antimatter was unknown to Einstein in 1915. Dirac’s theory4 appeared in 1928; the positron was observed5 in 1932. There has since been much speculation about gravity and antimatter. The theoretical consensus is that any laboratory mass must be attracted6 by the Earth, although some authors have considered the cosmological consequences if antimatter should be repelled by matter7,8,9,10. In the general theory of relativity, the weak equivalence principle (WEP) requires that all masses react identically to gravity, independent of their internal structure. Here we show that antihydrogen atoms, released from magnetic confinement in the ALPHA-g apparatus, behave in a way consistent with gravitational attraction to the Earth. Repulsive ‘antigravity’ is ruled out in this case. This experiment paves the way for precision studies of the magnitude of the gravitational acceleration between anti-atoms and the Earth to test the WEP

    Analysing and Modelling Particle Distributions in Near-Earth Space: Machine Learning

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    This thesis contains the analysis of 10 years of ESA Cluster observations using machine learning techniques. In the first study, we investigate solar wind electron populations at 1 au. In the second study, we apply a novel machine learning technique to magnetotail data in order to better characterise particle distribution function. In the third study, we make the first in-situ observations of the tearing instability leading to magnetic reconnection in the magnetotail. Solar wind electron velocity distributions at 1 au consist of three main populations: the thermal `core' population and two suprathermal populations called halo and strahl. We apply unsupervised algorithms to phase space density distributions, to perform a statistical study of how the core/halo and core/strahl breakpoint energies vary. The results of our statistical study show a significant decrease in both breakpoint energies against solar wind speed. By fitting Maxwellians to the core, based on our study, we can discuss the relative importance of the core temperature on halo and strahl electrons. Collisionless space plasma environments are characterised by distinct particle populations that typically do not mix. Although moments of their velocity distributions help in distinguishing different plasma regimes, the distribution functions themselves provide more comprehensive information about the plasma state. By applying dimensionality reduction and clustering methods to electron distributions in pitch angle and energy space, we distinguish between the different plasma regions. We identify several new distinct groups of distributions, that are dependent upon significantly more complex plasma and field dynamics. Magnetic reconnection is a fundamental mechanism responsible for explosive energy release in space and laboratory plasmas. The onset of reconnection is via the tearing instability. Due to its elusive nature, there is an absence of in-situ observations of the tearing instability. We present the first direct observations of the tearing instability and the subsequent evolution of plasma electrons and reconnection, using neural network outlier detection methods. Our analysis of the tearing instability and subsequent reconnection provides new insights into the fundamental understanding of the mechanism responsible for reconnection

    Medida del ángulo de mezcla de neutrinos θ₁₃ en el experimento Double Chooz

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    Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Atómica, Molecular y Nuclear, leída el 30-11-2015Depto. de Estructura de la Materia, Física Térmica y ElectrónicaFac. de Ciencias FísicasTRUEunpu

    Development of the Sliding Spark Technique for Trace Analytical Spectroscopy of Dielectric Solid Matrices

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    A novel direct solid-state emission spectroanalytical method based on the pulsed sliding spark source has been developed. The technique is characterised by a radiative transient discharge plasma propagating along the surface of a dielectric solid matrix enforced between a pair of electrodes in air at atmospheric pressure, where matrix excitation is driven by plasma-particle interaction based on geometry- and source opto-electric-modulated electron impact excitation. This dissertation embodies the results of the systematic theoretical and experimental study of the sliding spark which aimed at the analytical development of the technique for trace quantitative spectroscopy of the heavy elements embedded in the dielectric matrix surface layers. The optical emission spectrum, when detected and measured in the wavelength range 212511 nm at about 0.05 nm spectral resolution using optical fibre transmission in conjunction with a holographic blazed grating CCD spectrometer, was found to be suitable for simultaneous multi-elemental analysis. Investigation of the spectral characteristics of several heavy metals embedded in a variety of dielectric matrices (a boro-silicate simulate, borax, polyvinyl-alcohol, cellulose, teflon, Al-Zr simulate ceramic powder, simulate and River sediment samples) has led to the realisation of an empirical scheme for optimal identification and selection of the optically thin lines that are suitable for trace quantitative analysis. The utility of the lines depends on the element and sample matrix. Use of PVC as a matrix modifier results in increased sensitivity through formation of volatile halides. Comprehensive characterisation of the measured spectra provides empirical evidence to exploit the sliding spark at fast pulse frequency also as an atom source for combined emission, fluorescence, and absorption spectroscopy applicable to the elucidation of structural and molecular information by temporal gating, time-resolved techniques. Practical approaches found in the search for an appropriate calibration strategy for quantitative analysis include the use of internal standards based on Y and La (added) and Si and C (matrix-derived) spectral lines, which compensate for the differing ablation yield, signal drifts and matrix effects in and between complex matrices. Accurate analytical models have been derived for Mn, Ti, V, Ni, Co, Cu, Cd, Pb, Cr, Al, Fe, Zn, and Hg. A quantification methodology has been developed based on sediment and as model matrix, which combines high sensitivity and satisfactory reproducibility for Mn, Ti, V, Ni, Co, Cu, Cr, Al, Fe, and Zn. Trace quantitative analysis of dielectric solid matrices by sliding spark spectroscopy is realised in the concentration range from several hundred ppb to thousands of ppm depending on the analyte (and the spectral line utilized) and on the calibration strategy adopted for the quantification. The elemental limits of detection vary from several hundred ppb to few tens of ppm depending on the element, analysed matrix, spectral line, and calibration method. Qualitative speciation analysis is possible for Mn, V, Pb, Ti, Cu, and Co. Sliding spark spectroscopy has been validated as a new, simple but robust and versatile technique for the direct trace analysis of complex solid dielectric and refractory matrices with a reproducibility at 12 %, a precision characterised by a confidence interval of (0.510) %, and an accuracy by relative efficiency of 010 % by the successful analyses of Certified Reference Materials (Stream sediments), sewage sludge, a PVC polymer, an independent XRF laboratory analysis of River Rhine sediment, and by the results of comparative analyses made of the same elements using ICP and XRF (polarised radiation, 3-D Cartesian geometry) techniques

    Micromegas for the search of solar axions in CAST and low-mass WIMPs in TREX-DM

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    En este trabajo hemos estudiado la aplicación de los planos de lectura Micromegas, una estructura para la amplificación de la carga en detectores gaseosos, al campo de la detección de sucesos poco probables. En el experimento CAST para la detección de axiones; y en el proyecto TREX-DM para la búsqueda de WIMPs de baja masa. Tanto los axiones como los WIMPs son excelentes candidatos para formar la materia oscura del universo dado que no aparecen como solución ad hoc para resolverlo, sino que se propusieron para solucionar imporantes problemas del Modelo Estandard de física de partículas. Tanto los axiones como los WIMPs producirían un ritmo de sucesos extremadamente bajo y a muy bajas energías. Los detectores Micromegas pueden alcanzar niveles de fondo muy bajas y umbrales de energía por debajo del keV, debido a la granularidad del detector, radiopureza, unifromidad de la respuesta y alta ganancia. Pequeños detectores gaseosos de unos 3 cm de espesor se utilizan en el experimento CAST para la detección de los rayos-x inducidos por los axiones. En este trabajo se muestran los niveles de fondo alcanzados por los detectores del experimento, las técnicas de reducción de fondo y finalmente, en ausencia de una señal positiva, se obtienen límites a la constante de acoplo axion-fotón. Una versión similar, pero superior en tamaño se pretende utilizar para la detección de WIMPs de baja masa en el proyecto TREX-DM. TREX-DM pretende operar un detector a alta presión con un material blanco ligero equipado con planos de lectura Micromegas. Se describe el detector y la puesta a punto del mismo, así como los primeros resultados de la caracterización y la sensibilidad anticipada que puede alcanzar el experimento en caso de operar en un laboratorio subterráneo

    An assessment of the sensitivity of a low pressure time projection chamber to the direction of WIMP-induced nuclear recoils/

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    Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (pages 207-219).Direct directional detection of dark matter could provide an unambiguous observation of dark matter due to the predicted directional anisotropy of dark matter particles in the galactic reference frame. The Dark Matter Time Projection Chamber (DMTPC) collaboration develops TPCs with optical readout whose goal is the detection of the sense and direction of nuclear recoils generated by dark matter interactions with carbon and fluorine atoms in low pressure CF 4 gas, from which the direction of the incident dark matter particle can be inferred. The TPC contains a mesh based amplification stage that facilitates the two-dimensional imaging of nuclear recoil tracks using CCD cameras. Reconstructing the direction of recoils has been a subject of intensive R&D over the past several years, culminating in the design and construction of a current generation detector, the "4-shooter." The 4-shooter is prototyping several new detector techniques for a larger (1 m3 ) detector. The third dimension of recoils will be reconstructed in this detector using PMTs and the timing of induced charge signals in the detector amplification region. The 4-shooter's performance has being studied extensively on the surface of the Earth at MIT using alpha particles, low energy neutrons, and X-rays. This thesis reports on surface commissioning data taken with the 4-shooter.by Shawn Wesley Henderson.Ph.D

    Electron Scattering in Gases — from Cross Sections to Plasma Modeling

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    The first experiments on electron scattering were completed before the “official” discovery of this particle by J. J. Thomson. In spite of this, our knowledge of cross sections is still far from complete.More recent experiments had some unexpected results, like selective fragmentation of DNA constituents by low-energy electrons, or “reverse” phenomena, i.e., synthesis of simple amino acids from inorganic precursors, triggered by slow electrons. The most recent need for cross sections comes from modeling plasmas for industrial and thermonuclear applications, and atmospheres of solar and extra-solar planets.Both fundamental research (experiments, theory, reviews) and applications of electron-scattering cross sections in various processes are welcome

    The Second Conference on Lunar Bases and Space Activities of the 21st Century, volume 1

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    These papers comprise a peer-review selection of presentations by authors from NASA, LPI industry, and academia at the Second Conference (April 1988) on Lunar Bases and Space Activities of the 21st Century, sponsored by the NASA Office of Exploration and the Lunar Planetary Institute. These papers go into more technical depth than did those published from the first NASA-sponsored symposium on the topic, held in 1984. Session topics covered by this volume include (1) design and operation of transportation systems to, in orbit around, and on the Moon, (2) lunar base site selection, (3) design, architecture, construction, and operation of lunar bases and human habitats, and (4) lunar-based scientific research and experimentation in astronomy, exobiology, and lunar geology
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