Quantum electrodynamics (QED) predicts that the vacuum must be a non-linear optical medium: the speed of light in
the vacuum should decrease when the vacuum is subjected to intense electromagnetic fields. This amazing property of
vacuum has never been observed before. The DeLLight (Deflection of Light by Light) experiment seeks to measure this
effect using ultra-intense femtosecond laser pulses produced by the LASERIX platform (E =2.5J, 30fs, 10Hz) at the
IJCLab (Université Paris-Saclay). The innovative method of DeLLIght is to measure by interferometry the refraction of a
laser pulse (probe) of low energy, induced by the vacuum index gradient produced by an external pulse (pump) of high
intensity. The refraction of the probe pulse is detected using a Sagnac interferometer.
In this colloquium, I will start by explaining the scientific motivations of the study of the optical vacuum index, and the
few rare existing experimental tests. I will then describe the experimental method and the technical challenges of the
DeLLight project. Finally I will present the recent results obtained with the DeLLight pilot experiment, with low energy
pump laser pulses in air, validating the experimental method.
The next generation of collider detectors will make full use of Particle Flow algorithms, requiring full imaging calorimeters. The latter have been developed during the past 15 years by the CALICE collaboration and are now reaching maturity. The state-of-the-art and the remaining challenges will be presented for all investigated readout types. We will describe the commissioning, including beam test results, of large scale technological prototypes and the raw performances such as energy resolution, linearity and studies exploiting the distinct features of granular calorimeters regarding pattern recognition.
New results obtained in recent (2021/22) beam tests with technological prototypes will be available. Further, the design of experiments addressing the requirements and potential of imaging calorimetry will be discussed. In this context, the seminar will outline the R&D plans for the coming years that will put emphasis on timing and low-power readout.
The CALICE prototypes provide an unprecedented wealth of highly granular data of hadronic showers for a variety of active sensor elements and different absorber materials. I will discuss detailed measurements of the spatial and the time structure of hadronic showers to characterise the different stages of hadronic cascades in the calorimeters, in comparison with GEANT4-based simulations using different hadronic physics models. These studies also extend to the two different absorber materials, steel and tungsten, used in the prototypes. The high granularity of the detectors is exploited in the reconstruction of hadronic energy, both in individual detectors and combined electromagnetic and hadronic systems, making use of software compensation and semi-digital energy reconstruction. The results include new simulation studies that predict the reliable operation of granular calorimeters.
Granular calorimeters are also an ideal testing ground for the application of machine learning techniques. We will outline how these techniques are applied to CALICE data and in the CALICE simulation framework. At the beginning a lightweight introduction for a non-specialist audience to the physics of sampling calorimeters and the definition and motivation of the particle flow technique will be given.
Ce séminaire « spécial 40 ans du CPPM » se fera en français et s’adresse à tous les curieux du CPPM, qu’ils soient physiciens ou non. Je commenterai dix images qui illustrent les grandes étapes de notre voyage vers les deux infinis, de 1896 à nos jours. Nous partirons d’un phénomène bizarre, observé par Henri Becquerel en 1896, pour aboutir aux dernières découvertes auxquelles contribue le CPPM. J’évoquerai aussi l’impact sur notre vie quotidienne de ces découvertes et des prouesses techniques qu’elles ont permises.
5 derniers séminaires
Monolithic active pixel sensors (MAPS) have recently been used as building blocks of charged particles tracking and vertexing detectors because they offer lower material budget, higher granularity as well as a simpler assembly procedure and lower cost compared to the traditional wide spread hybrid technology.
The interest towards monolithic silicon sensors offering both excellent timing and position resolution has increased and different approches are being explored. Significant improvement of time resolution and speed of charge collection has recently been demonstrated on MAPS built on 180nm TowerJazz CMOS imaging technology and is currently being further explored on 65nm TowerJazz Panasonic Semiconductor (TPSCo) technology. This technology offers the possibility to build large sensors via stitching, giving green light to the construction of truly cylindrical tracker layers.
In this seminar I will describe recent and future use of MAPS to build charged particle trackers for colliders and space experiments.
Axionlike particles (ALPs) are candidates for dark matter that are strongly motivated by theory and are searched for in a plethora of experiments. At the Cosmic Axion Spin Precession Experiments (CASPEr) we exploit techniques based on nuclear magnetic resonance spectroscopy to probe possible non-gravitational couplings between dark matter and ordinary matter. This allows for sensitivity to ALPs over a large mass range, we currently aim to probe the range from 10-22 eV up to 2.5 10-6 eV. I will present our results obtained for various mass ranges and will discuss recent measurements at approximately 6 neV which are currently being analyzed. Attention will be paid to our work on the stochastic nature of the ALP field, daily and annual modulations, and gravitational lensing as well as methods to improve our sensitivity in future measurements.
Après une année 2022 hors norme, le changement climatique et ses impacts sont de toutes les conversations. Que savons-nous exactement aujourd'hui de ce changement ? Quels sont les différents futurs possibles vers lesquels nous nous dirigeons ? A quels impacts devons-nous nous préparer ? Pouvons-nous encore limiter ce réchauffement ?
La conférence que je donnerai abordera l'ensemble de ces questions. Elle permettra dans un premier temps de présenter les changements observés depuis le début du 20ème siècle, de réaliser un point sur l'état de nos connaissances sur ce changement, de mettre ce dernier en perspective des changements passés, et d'aborder les projections climatiques les plus récentes pour le 21ème siècle selon l'évolution à venir de nos émissions de gaz à effet de serre. La conférence s'intéressera ensuite aux impacts de ce changement, de plus en plus visibles année après année, en France mais également partout dans le monde, en raison d'une part de l’intensification des évènements météorologiques extrêmes et d'autre part des effets délétères de ce changement sur par exemple la biodiversité, la santé ou encore la ressource alimentaire. Enfin, la conférence se terminera par quelques mots dévoués aux enjeux et aux stratégies de l'adaptation ainsi qu'aux solutions qui peuvent être mises en place pour l'atténuation de ce changement.
CONCERTO is a new instrument that has been successfully installed in the Cassegrain Cabin of the APEX telescope in April 2021. It is a spectrometer with an instantaneous field of view exceeding 260 square arcminute and a spectral resolution up to 1.3 GHz. It is covering the frequency band 130-310 GHz. The main scientific aim of CONCERTO is to map in 3D the fluctuations of the [CII] line intensity in the reionisation and post-reionisation epoch (z>5). This technique, known as "intensity mapping", will allow us to address questions about the contribution of the dust-enshrouded star formation at z > 5, the history of metal enrichment, and the role of star-forming galaxies in shaping cosmic reionization. In addition to the main [CII] survey, we expect CONCERTO to bring a significant contribution in a number of areas, including the study of galaxy clusters (via the thermal and kinetic SZ effect), the observation of local galaxies, and the study of Galactic star-forming clouds. CONCERTO will also observe the CO intensity fluctuations arising from 0.3<z<2 galaxies, giving the spatial distribution and abundance of molecular gas at cosmic noon.
In this talk I will tell you the story of the CONCERTO adventure, from its conception to the first light. I will also review the major scientific goals of CONCERTO and show some first results.