Solar Axion search with Micromegas Detectors in the CAST Experiment with 3He as buffer gas

Axions are well motivated particles proposed in an extension of the Standard Model (SM) as a solution to the CP problem in strong interactions. On the other hand, there is the category of axion-like particles (ALPs) which appear in diverse extensions of the SM and share the same phenomenology of the axion. Axions and ALPs are hypothetical neutral particles that interact weakly with matter, being candidates to solve the Dark Matter problem. CAST, the CERN Axion Solar Telescope is looking for solar axions since 2003. CAST exploit the helioscope technique using a decommissioned LHC dipole magnet in which solar axions could be reconverted into photons. The magnet is mounted on a movable platform that allows tracking the Sun ~1.5 hours during sunset and during sunrise. The axion signal would be an excess of X-rays in the detectors located at the magnet bore ends and thus low background detectors are mandatory. Three of the four detectors operating at CAST are of the Micromegas type. The analysis of the data of the three Micromegas detectors during the 2011 data taking campaign at CAST is presented in this thesis, obtaining a limit on the coupling constant of gag < 3.90 x 10-10 GeV-1 at a 95% of confidence level, for axion masses from 1 to 1.17 eV. CAST Micromegas detectors exploit different strategies developed for the reduction of the background level: the intrinsic radiopurity of the detectors; the improvements on the manufacturing process; the event discrimination and the shielding. Moreover, different test benches have been developed in order to understand the origin of the background, in which the set-up at the LSC (Laboratorio Subterráneo de Canfranc) is the one that shows the lower background level. The state of art in low background techniques is shown in the upgrades of the Micromegas detectors at CAST, described in this work, which has led to a reduction of a factor ~6 of the background levels in the Micromegas detectors. It translates in an improvement of the sensitivity of CAST in a factor ~2.5. Beyond CAST a new generation axion helioscope has been proposed: IAXO-the International Axion Observatory. IAXO will enhance the helioscope technique by exploiting all the singularities of CAST implemented into a large superconducting toroidal magnet, dedicated X-ray optics and ultra-low background detectors attached at the end of the magnet bores. A description of the IAXO proposal and the study of the sensitivity of IAXO are presented in this thesis. IAXO will surpass the sensitivity of CAST in more than one order of magnitude, entering into an unexplored parameter space area and by first time in a favored region for axions and ALPs. The use of thin cavities inside long magnets for relic axion detection is particularly appealing, because this type of magnets are already used by the axion community in experiments looking for solar axions, like CAST and are projected in future searches like IAXO. A directional effect could be observed by the use of long thin cavities properly tuned. This case has been studied in this thesis and could provide a strong identificative signature of the direction of the CDM axions

Problemas resueltos de sistemas de telecomunicación (Vol. III)

Los problemas que se presentan en este libro están relacionados con los sistemas y servicios de telecomunicación que se estudian en las Escuelas de Ingeniería de Telecomunicación. Todos los problemas se explican detalladamente, utilizando las fórmulas y figuras necesarias para ayudar a la compresión de cada uno de ellos. Esta colección de problemas se ha estructurado en las siguientes partes: Niveles, Tráfico, Ruido, Medios de transmisión en línea, Comunicaciones móviles y Radioenlaces. En las dos primeras partes del libro se tratan materias básicas en el estudio de cualquier sistema de telecomunicaciones. Así, en la primera parte se hallan los problemas relacionados con la utilización de unidades y magnitudes en escala logarítmica. El manejo de estas unidades y magnitudes es fundamental para el diseño y comprensión de cualquier sistema de telecomunicaciones. En la segunda parte del libro se presentan los problemas relacionados con el estudio del tráfico de telecomunicaciones. Este estudio nos permitirá dimensionar de forma adecuada los servicios que se proporcionan en los sistemas de telecomunicación. Así, se aprende a calcular el número de canales necesario para satisfacer una cierta demanda de tráfico con una calidad predeterminada. Las dos siguientes partes del libro se refieren a aspectos más concretos de los sistemas de telecomunicaciones: en la tercera parte se hallan los problemas relacionados con el estudio y análisis del ruido en sistemas de telecomunicaciones y en la cuarta parte se encuentran problemas donde se calculan los parámetros primarios de un cable. Dichos parámetros son la resistencia, inductancia o capacitancia por unidad de longitud de un cable a partir de su geometría y de las características de los materiales que se han empleado en su fabricación (permitividad, conductividad, etc.), y se relacionan con los parámetros secundarios (impedancia característica, atenuación,) que son los que se suelen utilizar a la hora de planificar, por ejemplo, la instalación de un sistema de televisión por cable. En la quinta parte se encuentran los problemas cuya temática es general y no se ha podido asignar en los capítulos anteriores de forma única. En la sexta y séptima partes del libro se estudian dos sistemas reales de telecomunicaciones. La sexta parte se centra en la planificación de sistemas de comunicaciones móviles, y se revisan, por tanto, conceptos como el de la cobertura radioeléctrica y la planificación celular. En la séptima parte, se presentan problemas relacionados con las radiocomunicaciones punto a punto. Estos enlaces permiten en la actualidad la transmisión de gran volumen de datos entre dos puntos vía radio

Measurement of the nuclear modification factor for muons from charm and bottom hadrons in Pb+Pb collisions at 5.02 TeV with the ATLAS detector

Heavy-flavour hadron production provides information about the transport properties and microscopic structure of the quark–gluon plasma created in ultra-relativistic heavy-ion collisions. A measurement of the muons from semileptonic decays of charm and bottom hadrons produced in Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of 5.02 TeV with the ATLAS detector at the Large Hadron Collider is presented. The Pb+Pb data were collected in 2015 and 2018 with sampled integrated luminosities of and , respectively, and pp data with a sampled integrated luminosity of were collected in 2017. Muons from heavy-flavour semileptonic decays are separated from the light-flavour hadronic background using the momentum imbalance between the inner detector and muon spectrometer measurements, and muons originating from charm and bottom decays are further separated via the muon track's transverse impact parameter. Differential yields in Pb+Pb collisions and differential cross sections in pp collisions for such muons are measured as a function of muon transverse momentum from 4 GeV to 30 GeV in the absolute pseudorapidity interval . Nuclear modification factors for charm and bottom muons are presented as a function of muon transverse momentum in intervals of Pb+Pb collision centrality. The bottom muon results are the most precise measurement of b quark nuclear modification at low transverse momentum where reconstruction of B hadrons is challenging. The measured nuclear modification factors quantify a significant suppression of the yields of muons from decays of charm and bottom hadrons, with stronger effects for muons from charm hadron decays

Search for neutral long-lived particles in pp collisions at s \sqrt{s} = 13 TeV that decay into displaced hadronic jets in the ATLAS calorimeter

A search for decays of pair-produced neutral long-lived particles (LLPs) is presented using 139 fb−1 of proton-proton collision data collected by the ATLAS detector at the LHC in 2015–2018 at a centre-of-mass energy of 13 TeV. Dedicated techniques were developed for the reconstruction of displaced jets produced by LLPs decaying hadronically in the ATLAS hadronic calorimeter. Two search regions are defined for different LLP kinematic regimes. The observed numbers of events are consistent with the expected background, and limits for several benchmark signals are determined. For a SM Higgs boson with a mass of 125 GeV, branching ratios above 10% are excluded at 95% confidence level for values of c times LLP mean proper lifetime in the range between 20 mm and 10 m depending on the model. Upper limits are also set on the cross-section times branching ratio for scalars with a mass of 60 GeV and for masses between 200 GeV and 1 TeV

Determination of the parton distribution functions of the proton using diverse ATLAS data from pp collisions at vs = 7, 8 and 13 TeV

This paper presents an analysis at next-to-nextto-leading order in the theory of quantum chromodynamics for the determination of a new set of proton parton distribution functions using diverse measurements in pp collisions at √s = 7, 8 and 13 TeV, performed by the ATLAS experiment at the Large Hadron Collider, together with deep inelastic scattering data from ep collisions at the HERA collider. The ATLAS data sets considered are differential cross-section measurements of inclusive W± and Z/γ ∗ boson production, W± and Z boson production in association with jets, tt ¯ production, inclusive jet production and direct photon production. In the analysis, particular attention is paid to the correlation of systematic uncertainties within and between the various ATLAS data sets and to the impact of model, theoretical and parameterisation uncertainties. The resulting set of parton distribution functions is called ATLASpdf2

Search for single production of a vectorlike T quark decaying into a Higgs boson and top quark with fully hadronic final states using the ATLAS detector

A search is made for a vectorlike T quark decaying into a Higgs boson and a top quark in 13 TeV protonproton collisions using the ATLAS detector at the Large Hadron Collider with a data sample corresponding to an integrated luminosity of 139 fb−1. The Higgs-boson and top-quark candidates are identified in the all-hadronic decay mode, where H → bb¯ and t → bW → bqq¯0 are reconstructed as large-radius jets. The candidate Higgs boson, top quark, and associated B hadrons are identified using tagging algorithms. No significant excess is observed above the background, so limits are set on the production cross section of a singlet T quark at 95% confidence level, depending on the mass mT and coupling κT of the vectorlike T quark to Standard Model particles. In the considered mass range between 1.0 and 2.3 TeV, the upper limit on the allowed coupling valu

Search for associated production of a Z boson with an invisibly decaying Higgs boson or dark matter candidates at 13 TeV with the ATLAS detector

A search for invisible decays of the Higgs boson as well as searches for dark matter candidates, produced together with a leptonically decaying Z boson, are presented. The analysis is performed using proton−proton collisions at a centre-of-mass energy of 13 TeV, delivered by the LHC, corresponding to an integrated luminosity of 139 and recorded by the ATLAS experiment. Assuming Standard Model cross-sections for ZH production, the observed (expected) upper limit on the branching ratio of the Higgs boson to invisible particles is found to be 19% (19%) at the 95% confidence level. Exclusion limits are also set for simplified dark matter models and two-Higgs-doublet models with an additional pseudoscalar mediator

A new neural network technique for the design of multilayered microwave shielded bandpass filters

In this work, we propose a novel technique based on neural networks, for the design of microwave filters in shielded printed technology. The technique uses radial basis function neural networks to represent the non linear relations between the quality factors and coupling coefficients, with the geometrical dimensions of the resonators. The radial basis function neural networks are employed for the first time in the design task of shielded printed filters, and permit a fast and precise operation with only a limited set of training data. Thanks to a new cascade configuration, a set of two neural networks provide the dimensions of the complete filter in a fast and accurate way. To improve the calculation of the geometrical dimensions, the neural networks can take as inputs both electrical parameters and physical dimensions computed by other neural networks. The neural network technique is combined with gradient based optimization methods to further improve the response of the filters. Results are presented to demonstrate the usefulness of the proposed technique for the design of practical microwave printed coupled line and hairpin filters

Constraints on Higgs boson production with large transverse momentum using decays in the ATLAS detector

This paper reports constraints on Higgs boson production with transverse momentum above 1 TeV. The analyzed data from proton-proton collisions at a center-of-mass energy of 13 TeV were recorded with the ATLAS detector at the Large Hadron Collider from 2015 to 2018 and correspond to an integrated luminosity of 136 fb-1. Higgs bosons decaying into bb¯ are reconstructed as single large-radius jets recoiling against a hadronic system and are identified by the experimental signature of two b-hadron decays. The experimental techniques are validated in the same kinematic regime using the Z→bb¯ process. The 95% confidence-level upper limit on the cross section for Higgs boson production with transverse momentum above 450 GeV is 115 fb, and above 1 TeV it is 9.6 fb. The Standard Model cross section predictions for a Higgs boson with a mass of 125 GeV in the same kinematic regions are 18.4 fb and 0.13 fb, respectively

Numerical evaluation of the Green's functions for arbitrarily shaped cylindrical enclosures and their optimization by a new spatial images method

IIn this paper, a spatial image technique is used to efficiently calculate the mixed potential Green’s functions associated with electric sources, when they are placed inside arbitrarily shaped cylindrical cavities. The technique is based on placing electric dipole images and charges outside the cavity region. Their strength and orientation are thencalculated by imposing the appropriate boundary conditions for the fields at discrete points on the metallic wall. A method for the assessment of the potentials accuracy is proposed, and several optimization techniques are presented. Three cavities are analyzed to demonstrate the usefulness of the techniques. The cutoff frequencies and potentials patterns are compared to those obtained by a standard finite elements technique, showing excellent agreement. Finally, a band-pass filter based on coupled lines is analyzed, demonstrating the practical value of the technique.This work has been developed with support from the Spanish National Project (CICYT) with reference TEC2004-04313-C02-02/TCM, and the Regional Seneca Project with reference 02972/PI/0