Section de physique Département de physique nucléaire et corpusculaire

Semestre d'Été 2007

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Prof. Christoph Paus, MIT - Observation of Bs Mixing with the CDF Experiment

A long quest of about 20 years for the search of Bs Meson mixing has ended with the announcement of its observation in September 2006. The phenomenon of a particle changing into its own anti particle at a rate of about 3 trillion, in agreement with the Standard Model expectation, has been identified in a tour de force analysis at the CDF experiment.

Dr Aran Garcia-Bellido, University of Washington - Evidence for Production of Single Top Quarks at D0 and A First Direct Measurement of |Vtb|

Since 1995, top quarks have been observed in particle-antparticle pairs produced via the strong interaction at the Fermilab Tevatron ppbar collider. But top quarks can also be produced singly via the electroweak interaction. I will present evidence for the production of single top quarks in the DZERO data with an integrated luminosity of 0.9 fb-1. To isolate the signal from the large backgrounds, we have used three different multivariate analyses. I will discuss the results and their significance, and present the first direct measurement of the CKM matrix element |Vtb| > 0.68 at the 95% confidence level assuming standard model couplings. Fichier .pdf de la présentation

Dr Seven Bass, CERN/Innsbruck- Precision measurements in spin physics

The proton spin problem has been challenging experimentalists and theorists alike for the last 20 years. Polarized deep inelastic scattering experiments at CERN, DESY and SLAC have told us that quark partons contribute only about 30% of the proton's spin whereas relativistic quark models predict 60%. Where is the missing spin and why is the quark spin contribution so small ? In this talk I will give an overview of the proton spin problem and what it may be telling us about QCD, the vacuum and dynamical symmetry breaking. A precise measurement of neutrino-proton elastic scattering would make a vital contribution to resolving many of the outstanding issues.

Dr Antonio Limosani, KEK, Japon - Semileptonic and Radiative B-meson decays

The success of the B Factories at KEK and SLAC has furthered our knowledge of CP violation, a necessary ingredient for the creation of a matter-dominanted universe. Ever increasing data samples has ushered in a new era of precision CP measurements, in which the unitarity of the Cabibbo-Kobayashi-Maskawa matrix is examined for signs of New Physics. One of the crucial pieces of information, surprisingly, comes not from CP violation but from studies of semileptonic decays of the B mesons. I will discuss how various measurements of semileptonic and radiative B decays combine together to provide a precision measurement of the CKM matrix element |Vcb| and to determine the value of smallest CKM matrix element |Vub| and how such measurements depend upon progress in the theory of B decays.

Prof. Guido Drexlin, Karlsruhe Institute of Technology KIT - KATRIN - direct measurement of neutrino masses with sub-eV sensitivity

The major scientific objective of the international Karlsruhe Tritum Neutrino (KATRIN) Experiment is the model independent measurement of the electron neutrino mass in tritium beta decay with a sensitivity of 200 meV. In the cosmological context, this allows to investigate whether massive relic neutrinos left over from the Big Bang play a specific role as hot dark matter in the evolution of large scale structures of the universe. In particle physics KATRIN will allow to discriminate between different neutrino mass models (either of quasi-degenerate or hierarchical pattern).
The key components of KATRIN comprise an ultra-luminous windowless gaseous molecular tritium source, an electron transport and tritium elimination system, a tandem of electrostatic spectrometers with the tasks of energy pre-filtering and analysis (?E=1 eV) and a detector for ß-counting.
The talk gives an overview of the motivations for a next generation direct neutrino mass experiment as well as of the current project status. Special emphasis is put on the large main spectrometer with its diameter of 10 m and a length of 24 m, which is currently being commissioned on the site of Forschungszentrum Karlsruhe after an 8800 km voyage around Europe.
Finally the neutrino mass sensitvity of KATRIN is discussed and the implications of KATRIN for cosmology and particle physics are outlined.

Dr Saverio Braccini, Inselspital, University Hospital of Berne - Present and future of hadrontherapy

Hadrontherapy is a novel technique of cancer radiation therapy which employs beams of charged hadrons, protons and carbon ions in particular. Due to their physical and radiobiological properties, they allow to obtain a more conformal treatment with respect to photons used in conventional radiation therapy, sparing better the healthy tissues and allowing a better control of the disease. Hadrontherapy is the direct application of research in particle physics making use of specially conceived particle accelerators and detectors. Protons can be considered today a very important tool in clinical practice due to the several hospital-based centres in operation and to the continuously increasing number of proposed centres worldwide. Very promising results have been obtained with carbon ion beams in Germany and Japan and two hospital-based centres are now under construction in Europe. The present status of hadrontherapy is reviewed together with some innovative ideas issued form particle physics.

Dr Thomas Schietinger, PSI - Proposal to measure the muon electric dipole moment with a compact storage ring at PSI

In the Standard Model, lepton electric dipole moments (EDM) arise from the CP-violating phase in the CKM matrix at the three-loop level only, resulting in values that are many orders of magnitude below the sensitivity of current and future experiments. Lepton EDMs therefore offer an excellent opportunity to discover unambiguous evidence for new CP-violating phases, as called for by the baryon-antibaryon asymmetry of the universe. The muon EDM is one of the least constrained fundamental properties in elementary particle physics. We propose to utilize the large available flux of polarized muons at PSI to search for a muon EDM down to the level of $5 \times 10^{-23}\, e$ cm, about four orders of magnitude below the current limit. The experiment consists of a very compact storage ring (42 cm radius), in which a radial electric field compensates the g-2 precession, thereby greatly enhancing the sensitivity to a possible EDM-induced spin precession.

Dr Giles Gerbier, CEA/DAPNIA - À la recherche de la Matière Noire : état actuel et futur d'Edelweiss

Edelweiss est une expérience européenne, installée dans le Laboratoire Souterrain de Modane dans les Alpes, consacrée à la recherche de WIMP's, particules candidates pour expliquer la Matière Noire. Après un bref rappel sur la place grandissante qu'occupe cette question dans le contexte de la compréhension de notre univers, je donnerai les principes de fonctionnement des détecteurs cryogéniques en Germanium utilisés dans Edelweiss. Je présenterai ensuite les résultats obtenus dans la première étape Edelweiss I (phase 1 kg) et l'état actuel d'Edelweiss II (phase 9 kg), en période de validation et sa phase finale (30 kg). L'accent sera mis sur la compréhension des bruits de fond, les moyens de les éliminer et les prédictions de sensibilité dans les années à venir, en perspective avec les autres expériences concurrentes et les modèles de théorie supersymétrique. Le futur à long terme, en particulier le projet EURECA, sera évoqué.

Prof. A. Baldini, INFN, Pisa - A sensitive test of supersymmetric-GUT theories: the MEG experiment at PSI

The µ -> e gamma decay, which is absent in the Standard Model, is instead foreseen to occur in supersymmetric grand unified theories (SUSY-GUT) with a branching ratio which should be detectable by the MEG experiment. In this seminar the SUSY-GUT predictions for the µ -> e gamma decay rate and the connection with neutrino oscillations will be illustrated. The status of the MEG experiment will be described and the foreseen experimental sensitivity to the µ -> e gamma decay will be shown.

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Semestre d'Hiver 2006-2007

Dr Stefan Schoenert - Max-Planck-Institut fuer Kernphysik Heiderlberg - The Germanium Detector Array (GERDA) for the search of neutrinoless double beta decays of ⁷⁶Ge at LNGS line

The Germanium Detector Array (GERDA [1]) for the search of neutrinoless double beta decays of ⁷⁶Ge at LNGS will operate bare germanium diodes enriched in ⁷⁶Ge in an (optional active) cryogenic fluid shield to investigate neutrinoless double beta decay with a sensitivity of T_{1/2} > 2 x 10²⁶~years after an exposure of 100~rm kg x rm years. In this talk, I shall introduce the relevance of neutrinoless double beta decay, the experimental concepts of GERDA, the challenges and techniques to reduce backgrounds to neutrinoless double beta decay, and summarize the status of the project.

Dr Minh Quang TRAN - EPFL - ITER and the way toward a fusion reactor

Fusion is a possible source of electricity for base load, which is compatible with a sustainable development. The talk will first present the physics basis for the realisation of fusion and discuss the main aspects with respect to "fuel" resources, environment impact, safety and cost of electricity. The next generation of fusion devices ITER will produce 500 MW of (thermal) fusion power. The challenges of and R&D towards ITER will be outlined. The steps following ITER along the roadmap towards the first reactor producing electricity will be discussed, highlighting the major necessary development in material science and technology. Fichier .ppt de la présentation

Dr Carlos Gamez Pérez - Scientific Strategies in Anomalous Contexts : High Energy Physics in Spain and the Dictatorship of General Franco

Which is the perfect context for the rise and development of a scientific discipline? This is the most important question we try to answer when studying the case of High Energy Physics in Spain during the Dictatorship of General Franco. This communication analyses the relation between science and politics, the problem of tradition in science (concretely in physics), the relation between different scientific specialities like nuclear physics, the international influence on the Spanish community of Theoretical Physics and the political and scientific strategies made by the small Spanish community of High Energy Physics in order to succeed (at least partially) in growing into a scientific community.

In a methodological point of view, we can explain the difficulties in the construction of new historical sources in contemporary Physics by compiling documentation or making interviews or questionnaires.

Dr Michael MOLL, CERN - Radiation Tolerant Sensors for Solid State Tracking Detectors

The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 1035 cm 2 s-1 will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi-3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices.
These and other most recent advancements of the RD50 collaboration, as well as an overview of the present understanding of the radiation induced microscopic processes leading to the deterioration of silicon detector properties, are presented and discussed. Fichier .pdf de la présentation.

Prof. Olivier Martineau-Huynh, LPNHEP, IN2P3, France - Astronomie gamma avec H.E.S.S.

L’expérience H.E.S.S. (High Energy Sterescopic System) est en train de marquer le domaine de l’astronomie gamma. Composée de quatre télescopes à effet Cerenkov installés en Namibie, elle a en effet permis la découverte en 3 ans de plus de 20 nouveaux émetteurs de rayonnement électromagnétique multi-TeV, alors qu’une dizaine seulement avaient été découverts au cours des deux décennies précédentes. Après une rapide présentation des sources possibles de rayonnement gamma au TeV, j’expliquerai le principe de détection des télescopes Cerenkov puis détaillerai les résultats les plus marquants obtenus par H.E.S.S. au cours des trois dernières années. Je présenterai certains des objets étudiés par H.E.S.S. (par exemple la première source périodique au TeV, ou la galaxie radio M87), et soulignerai l’apport de H.E.S.S. à notre connaissance des rayons cosmiques et à la cosmologie. Fichier .pdf de la présentation

Prof Erwin Flueckiger, Université de Berne - Solar Flares

Solar flares are generally defined as "rapid releases of energy from a localized region on the Sun in the form of electromagnetic radiation, energetic particles, and mass motions". Although the first record of a solar flare in the scientific literature dates back to 1859, the physical processes involved in these high-energy phenomena are still far from being fully understood. Significant progress, however, has been achieved in the understanding of the scenarios of gradual and impulsive flares, their relation to coronal mass ejections, and the acceleration of particles up to relativistic energies. Using recent examples like the January 20, 2005 event, characteristic signatures of solar flares at the Sun, in interplanetary space, and at the Earth, are reviewed, and the significance of different observational techniques is addressed.

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Last updated: 9 mars 2010, Blanchard Catherine