EASIER : Identification de gerbe atmosphérique par radiomètre électronique

Ultra high energy cosmic ray composition is crucial to determine their source. Current techniques measure it with a limited duty cycle of 10%.The EASIER project (Extensive Air Shower Identification using Electron Radiometer) is a radio detection system integrated with the surface detector of the Pierre Auger Observatory. Its goal is the measurement of the mass composition at high energy via the observation of the electromagnetic profile of air showers with a 100% duty cycle.The principle of EASIER was applied in the VHF band (30-80 MHz) in which a coherent signal was already observed and in the C band (3.4-4.2 GHz) in which an isotropic emission is expected.A large part of this thesis describes the developments and calibration of the experimental setups in both bands.The installation of 7 detectors in the VHF band led to the detection of 36 events. Their characteristics indicate an emission beamed around the shower axis with a characteristic distance of the order of 200m for vertical showers.In the C band, 7 detector units were installed and led to the first detection of a radio signal in this band. The extension to 61 units raised the number of candidates to 4, all detected at distances to the shower axis lower than 300m. The comparison with simulations allowed us to set limits on the parameters of an isotropic emission.The distances of detection are limited by the emission mechanism and are up to now too small to fulfil EASIER goals. Improvements are underway to lower the sensitivity in both bands.La composition des rayons cosmiques d ‘ultra haute énergie est une information cruciale pour déterminer leur source. Les techniques actuelles la mesure avec un cycle utile limité a 10%. Le projet EASIER (Extensive Air Shower Identification using Electron Radiometer) est un système de détection radio intégré au détecteur de surface de l'Observatoire Pierre Auger. L’objectif est la mesure de la composition à hautes énergies (E > 10EeV) par l’observation du profile électromagnétique avec un cycle utile de 100%. Le principe d’EASIER a été appliqué dans la bande VHF (30-80 MHz) dans laquelle un signal radio cohérent a déjà été observé et dans la bande C (3.4-4.2 GHz) dans laquelle une émission isotrope est attendue. Une partie importante de cette thèse décrit les développements et la caractérisation des dispositifs expérimentaux dans ces deux bandes. L’installation de 7 détecteurs dans la bande VHF a permis la détection de 36 événements. Leurs caractéristiques indiquent une émission concentrée autour de l’axe de la gerbe avec une distance caractéristique de l’ordre de 200m pour des gerbes verticales. Dans la bande C un prototype de 7 unités a permis la première détection d'un signal radio dans cette bande. L’extension à 61 unités porte le nombre de candidats à 4, tous détectés à des distances à l’axe inferieures à 300m. La comparaison avec des simulations a permis d’établir des limites sur les caractéristiques d’une émission isotrope.Les distances de détection sont contraintes par les mécanismes d’émission observés et restent trop faibles pour remplir les objectifs d’EASIER. Des développements sont en cours pour abaisser la sensibilité des détecteurs dans les deux bandes

Studies of the microwave emission of extensive air showers with GIGAS and MIDAS at the Pierre Auger Observatory

International audienceIn 2008, a radio signal interpreted as Molecular Bremsstrahlung Radiation (MBR)was detected at SLAC at microwave frequencies from electromagnetic showersproduced in beam test experiments. Due to the isotropic nature of MBR and itsinsensitivity to atmospheric attenuation and light conditions, it would allowthe measurement of the shower longitudinal profile with an almost 100% dutycycle compared to 15% at most with the fluorescence technique today. Severalexperiments either in the laboratory or in situ within cosmic-ray observatorieshave been set up aiming at the detection of the MBR flux. The Pierre AugerObservatory has been used as the base for two experiments pursuing the detectionof the MBR at GHz frequencies. MIDAS is a radio telescope instrumented with aparabolic dish focusing the radio signal on an array of 53 horn antennas and hastaken data for 2 years. GIGAS on the other hand is a single antenna detectorembedded in a surface detector. It was implemented in three different versionswith a gradually improved sensitivity to comply with the evolution in theexpected MBR intensity. We review these two experimental efforts undertaken atthe Pierre Auger Observatory attempting at MBR detection and present theirlatest results. EASIER Antenna SD electronics box EASIER box PMT PMT PMT Figure1: Left: The GIGAS arrays and MIDAS field of view overlaid with the surfacedetector of the Pierre Auger Observatory. Right: Scheme of GIGAS concept. Thesensor placed on the tank is one the three antenna shown in the left side. Thesignal chain common for all the setups is represented on the bottom part

Observation of radio emissions from electron beams using an ice target

To observe high energy cosmogenic neutrinos above 50 PeV, the large neutrino telescope ARA is being built at the South Pole. The ARA telescope detects neutrinos by observing radio signals by the Askaryan effect. We performed an experiment using 40 MeV electron beams of the Telescope Array Electron Light Source to verify the understanding of the Askaryan emission as well as the detector responses used in the ARA experiment. Clear coherent polarized radio signals were observed with and without an ice target. We found that the observed radio signals are consistent with simulation, showing that our understanding of the radio emissions and the detector responses are within the systematic uncertainties of the ARAcalTA experiment which is at the level of 30%

Study of Microwave Radiation from the Electron Beam at the Telescope Array Site

International audienceThe Telescope Array (TA) experiment installed the electron accelerator in order to calibrate the fluorescence detector by shooting 40 MeV electrons into the atmosphere. This accelerator also works to investigate the radio detection techniques used for the cosmic ray observations. Using this accelerator, four experimental groups have studied individual radio detection methods at different frequency bands ranging from 50 MHz to 12 GHz. All of these experiments have observed the microwave radiation from the electron beam itself. We have studied the radiation by combining all the measured results and constructed a model of this phenomena. Results of four experiments and model expectation are in good agreement within the systematic uncertainty

XeLab: a test platform for xenon TPC instrumentation

International audienceXenon double phase TPCs have shown the best sensitivities for dark matter direct searches over a large parameter space.However difficulties in the construction large scale TPC have already arisen in the current detectors and will be even more challengingin the next generation one. Of critical importance are the construction of meter scale electrodes with negligible sagging and high optical transparencybut also the control of instrumental background such as single electron emission. Xelab is a system equipped with a small double phase xenon TPCcooled with liquid nitrogen and a xenon recuperation module primarily designed for the test of innovative concept of floating electrodesbut will also serve as a platform for instrumental development for xenon based TPC.We present the design and realisation of XeLab and the baseline of electrodes that we plan to test

Coherent radio emission from the electron beam sudden appearance

International audienceWe report on radio frequency measurements of the electron beam sudden appearance signal from the Telescope Array Electron Light Source (TA-ELS). The TA-ELS is constructed to calibrate the Telescope Array fluorescence telescope, and as such it can be used to mimic a cosmic-ray or neutrino induced particle cascade. This makes the TA-ELS the perfect facility to study new detection techniques such as the radio detection method. We report on the data obtained by four independent radio detection set-ups. Originally searching for either the direct Askaryan radio emission, or a radar echo from the induced plasma, all these experiments measured a very strong transient signal when the beam exits the accelerator. Due to the different scope of the individual experiments, we have detected the beam sudden appearance signal at different frequencies, ranging between 50 MHz and 12.5 GHz. The direct application in nature for this signal is found in cosmic-ray or neutrino induced particle cascades traversing through different media, such as air, ice, and rock. These measurements are compared to the theoretical predictions for this signal, where it follows that theory and experiment match very well over the full spectrum

Observation of inclined EeV air showers with the radio detector of the Pierre Auger Observatory

International audienceWith the Auger Engineering Radio Array (AERA) of the Pierre Auger Observatory, we have observed the radio emission from 561 extensive air showers with zenith angles between 60o and 84o. In contrast to air showers with more vertical incidence, these inclined air showers illuminate large ground areas of several km2 with radio signals detectable in the 30 to 80 MHz band. A comparison of the measured radio-signal amplitudes with Monte Carlo simulations of a subset of 50 events for which we reconstruct the energy using the Auger surface detector shows agreement within the uncertainties of the current analysis. As expected for forward-beamed radio emission undergoing no significant absorption or scattering in the atmosphere, the area illuminated by radio signals grows with the zenith angle of the air shower. Inclined air showers with EeV energies are thus measurable with sparse radio-antenna arrays with grid sizes of a km or more. This is particularly attractive as radio detection provides direct access to the energy in the electromagnetic cascade of an air shower, which in case of inclined air showers is not accessible by arrays of particle detectors on the ground