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

Development of time projection chambers with micromegas for Rare Event Searches

The Rare Event Searches is a heterogeneous field from the point of view of their physical motivations: double betha neutrinoless decay experiments, direct detection of WIMPs as well as axions and other WISPs (candidates for the DM, but also motivated by other questions from Particle Physics). The field is rather defined by the requirements of these experiments, essentially a very sensitive detector with low background which is usually operated in underground laboratories. The availability of a rich description of the event registered by the detector is a powerful tool for the discrimination of the signal from the background. The topological description of the interaction that can be delivered by a gaseous TPC is a useful source of information about the event. The generic requirements for a gaseous TPC that is intended for rare event searches are very good imaging capabilities, high gain and efficiency, stability and reliabiligy and radiopurity, which could imply working with particular gases, in absence of quencher and at high pressure, high granularity and the use of state-of-the-art electronics, and everything must be scalable to higher detectors. Such requirements could be fulfilled by TPCs because they are equipped with Micro-Pattern Gas Detectors, like Micromegas. The phenomenology of TPCs is studied in detail and R&D activities to its application to rare event searches are reported, in particular regarding microbulk micromegas, the latest manufacturing technique. A big part of the work has been devoted to the development of libraries and programs for generic Monte Carlo simulations on low energy TPCs and micromegas specific processes (primary charge generation, drift processes, implementation of the readout, generation of the electronic signals) and associated tools for information management and interpretation of the results. The role micromegas detectors have played in the CAST (CERN Axion Solar Telescope) experiment is reviewed, describing the strategies followed to improve the background more than a factor of 50, since the beginning of the experiment to 2011. To provide more precise guidelines aiming to continue and accelerate the encouraging evolution of micromegas backgound in CAST and to deliver prospects for IAXO (International AXion Observatory) an study on the CAST micromegas background is carried out relying in both simulations and tests-benches. Underground operation of CAST detector with a heavy shielding (at least 10 cm lead thickness) and improved radiopurity produced a background about 30 times lower than CAST nominal background, demonstrating the potencial of the detectors. The success of the 2012 upgrade of two of the CAST micromegas detectors, leading to an improvement of a factor 5 in background level, has been the first application/confirmation of the conclusions from these studies. In conclusion, the prospects to the application of micromegas to rare event searchers are encouraging for the issues that were proposed. The tests on the different aspects of the micromegas operation that are demanded by rare event searches (high pressure, particular mixtures, absence of quench) produced encouraging results. Moreover the state-of-the-art micromegas manufacturing technique, microbulk, has been measured to be radiopure. The impressive progression of the background of CAST micromegas detectors may be the most significant milestone. There has been an important advance in the understanding of the background nature, the potential of the different applied strategies and the way the detector performance and the analysis methods interact with the different kinds of background events. It can be assured that this progression, which have improved more than two orders of magnitude from the first micromegas installation, will not stop in the present sunset background level, and the future IAXO helioscope will be provided with more sensitive micromegas detectors. The ultra-low background obtained in the LSC (which is only an upper bound, probably no a real limit for the micromegas) is one of the facts that support this assertion. But its significance goes beyond the application to helioscopes. It demonstrates the possibility of registering ultra-low background below 10 keV with a low energy threshold

Detección de WIMPs con el detector TREX-DM

En este trabajo se aborda la cuestión de la materia oscura: evidencias y principales estrategias de búsqueda; y el detector TREX-DM en la búsqueda de WIMPs de baja masa: en qué consiste el experimento, como se recoge la señal y su situación actual.Se presenta el modelo de halo de materia oscura y se calculan los ritmos de interacción con distintos elementos para un WIMP sin espín de distintas masas.Además se realiza un análisis de sobre la uniformidad de la ganancia en uno de los dos detectores Micromegas que emplea TREX-DM con una calibración de cadmio 109 y esta información se utiliza para corregir espectros de energía.<br /

Experimento IAXO para la detección de axiones: señal y fondo en el prototipo IAXO-D0

En esta memoria se lleva a cabo una introducción al mundo axiónico, analizando el surgimiento de esta partícula hipotética, sus propiedades, su candidatura como Materia Oscura y las principales estrategias de detección directa, entre las que destaca IAXO, helioscopio de cuarta generación en el que se centra este trabajo, cuyo objetivo es valorar si es factible en términos de sensibilidad y ganancia el cambio del gas activo del detector de argón a xenón para disminuir el nivel de fondo y mejorar la eficiencia del conjunto. En base a los resultados arrojados por la cámara TREX-0 en la comparación de ganancias relativas máximas entre la mezcla de Ar+2%Iso y distintas mezclas de Xe+Ne+Iso, se plantean dos hipótesis acerca del factor de ganancia entre ambas mezclas, una menos conservadora que la otra, cuya confirmación exige futuras medidas por parte de la colaboración.<br /

Estudio sobre la producción de axiones en el Sol y su detección en helioscopios de axiones

Estudio bibliográfico sobre axiones, abarcando qué son, qué motivos justifican su existencia más allá del Modelo de Estándar de Partículas actual, cómo interaccionan con la materia, cómo se producen y cómo se pueden detectar. Aplicación posterior de esos conocimientos en la obtención de la curva de sensibilidad de dos experimentos, IAXO y BabyIAXO, cuyo objetivo es detectar axiones solares. Además, se propone una alternativa a la fase II de estos experimentos, redistribuyendo el tiempo de medida para buscar en distintos valores del rango de parámetros de la masa del axión y su constante de acoplo con fotones.<br /

Estudio del efecto de los fondos ambientales en la sensibilidad del experimento BabyIAXO a axiones solares

En esta memoria se lleva a cabo una introducción teórica sobre la física de axiones (QCD y ALPs), analizando su origen, propiedades y consecuencias de su existencia. También se trata las diferentes estrategias de detección experimentales, centrándose en los helioscopios, en concreto, IAXO y su prototipo BabyIAXO. IAXO será el primer helioscopio de cuarta generación que permita estudiar regiones del espacio de parámetros hasta ahora no alcanzadas con otros experimentos debido a su alta sensibilidad. El objetivo de este trabajo consiste en estudiar un centelleador líquido que permita aprovechar el montaje de IAXO para la detección de axiones de supernova. En base a los resultados obtenidos de las simulaciones de este trabajo se establecen las dimensiones y el material (proporción de plomo diluido) que podría presentar el centelleador, así como las condiciones que tendrían que presentar las diferentes estrategias de reducción de fondo de fotones cósmicos. En este caso, las estrategias de reducción de fondo que se tienen en cuenta son: el uso de un blindaje de plomo, estableciendo el grosor del mismo, y establecer un sistema de vetos, determinado el grosor y una energía umbral en los vetos. Para alcanzar el ritmo deseado del centelleador (~0.1 Hz), al menos, durante la ventana de emisión de axiones de una supernova será necesario realizar un estudio sobre la topología de los fotones cósmicos en el detector para implementar cortes más sofisticados.<br /

El axión como solución a la Materia Oscura del Universo: estrategias para su detección

En esta memoria se revisan las distintas evidencias observacionales que apuntan a la existencia de la materia oscura, y se estudia un posible candidato a componerla: el axión. Asimismo, se recogen las distintas estrategias propuestas para su detección, junto con las restricciones en su masa y acoplamiento con fotones deducidas de distintos experimentos. Por último, se incluye una serie de resultados de simulaciones realizadas en el contexto del experimento IAXO (International Axion Observatory), que serán de utilidad en la puesta en marcha del mismo

Direct detection of dark matter axions with directional sensitivity

We study the directional effect of the expected axion dark matter signal in a resonant cavity of an axion haloscope detector, for cavity geometries not satisfying the condition that the axion de Broglie wavelength $\lambda_a$ is sufficiently larger than the cavity dimensions $L$ for a fully coherent conversion, i.e. $\lambda_a \gtrsim 2\pi L$. We focus on long thin cavities immersed in dipole magnets and find, for appropriately chosen cavity lengths, an O(1) modulation of the signal with the cavity orientation with respect the momentum distribution of the relic axion background predicted by the isothermal sphere model for the galactic dark matter halo. This effect can be exploited to design directional axion dark matter detectors, providing an unmistakable signature of the extraterrestrial origin of a possible positive detection. Moreover, the precise shape of the modulation may give information of the galactic halo distribution and, for specific halo models, give extra sensitivity for higher axion masses.Comment: 14 pages, 12 figures, prepared for submission to JCA

Wnt-3a Induces Epigenetic Remodeling in Human Dental Pulp Stem Cells

Dental pulp stem cells (DPSCs) from adult teeth show the expression of a very complete repertoire of stem pluripotency core factors and a high plasticity for cell reprogramming. Canonical Wnt and Notch signaling pathways regulate stemness and the expression of pluripotency core factors in DPSCs, and even very short-term (48 h) activations of the Wnt pathway induce a profound remodeling of DPSCs at the physiologic and metabolic levels. In this work, DPSC cultures were exposed to treatments modulating Notch and Wnt signaling, and also induced to differentiate to osteo/adipocytes. DNA methylation, histone acetylation, histone methylation, and core factor expression levels where assessed by mass spectroscopy, Western blot, and qPCR. A short-term activation of Wnt signaling by WNT-3A induced a genomic DNA demethylation, and increased histone acetylation and histone methylation in DPSCs. The efficiency of cell reprogramming methods relies on the ability to surpass the epigenetic barrier, which determines cell lineage specificity. This study brings important information about the regulation of the epigenetic barrier by Wnt signaling in DPSCs, which could contribute to the development of safer and less aggressive reprogramming methodologies with a view to cell therapy.This work was funded by the UPV/EHU (GIU16/66, UFI 11/44; to F.U.), the Basque Government (GV/EJ; Ikerketa Taldeak IT831-13; to G.I. and ELKARTEK KK-2019-00093; to F.U.) and ISCIII (DTS18/00142; to N.S.)

Osteogenic differentiation of human dental pulp stem cells in decellularised adipose tissue solid foams

3D cell culture systems based on biological scaffold materials obtainable from both animal and human tissues constitute very interesting tools for cell therapy and personalised medicine applications. The white adipose tissue (AT) extracellular matrix (ECM) is a very promising biomaterial for tissue engineering due to its easy accessibility, malleability and proven biological activity. In the present study, human dental pulp stem cells (hDPSCs) were combined in vitro with ECM scaffolds from porcine and human decellularised adipose tissues (pDAT, hDAT) processed as 3D solid foams, to investigate their effects on the osteogenic differentiation capacity and bone matrix production of hDPSCs, compared to single-protein-based 3D solid foams of collagen type I and conventional 2D tissue-culture-treated polystyrene plates. pDAT solid foams supported the osteogenic differentiation of hDPSCs to similar levels to collagen type I, as assessed by alkaline phosphatase and alizarin red stainings, reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) and osteocalcin/bone gamma-carboxyglutamate protein (BGLAP) immunostaining. Interestingly, hDAT solid foams showed a markedly lower capacity to sustain hDPSC osteogenic differentiation and matrix calcification and a higher capacity to support adipogenesis, as assessed by RT-qPCR and oil red O staining. White ATs from both human and porcine origins are relatively abundant and available sources of raw material to obtain high quality ECM-derived biomedical products. These biomaterials could have promising applications in tissue engineering and personalised clinical therapy for the healing and regeneration of lesions involving not only a loss of calcified bone but also its associated soft non-calcified tissues.This research was supported by the Basque Government (ELKARTEK program PLAKA KK- 2019-00093; to NB), MICINN retos I+D+i (PID2019- 104766RB-C21, to JRP) and UPV/EHU (PPGA20/22; to FU, GI). The authors would like to thank the staff members of the SGIKER services of the UPV/EHU: Lipidomic service (Beatriz Abad) and Analytical Microscopy (Ricardo Andrade, Alejandro Díez-Torre and Irene Fernández) for their technical assistance