Section de physique Département de physique nucléaire et corpusculaire

Semestre d'Été 2006

Prof. Nicolas Prantzos, CNRS, Paris - Gamma-ray line astronomy

Gamma-ray lines from cosmic sources provide unique isotopic information, since they originate from energy level transitions in the atomic nucleus. Gamma-ray telescopes explored this astronomical window in the past three decades, detecting radioactive isotopes that have been ejected in interstellar space by cosmic nucleosynthesis events. Astronomical gamma-ray telescopes feature standard detectors of nuclear physics, but have to be surrounded by effective shields against local instrumental background, and need special detector and/or mask arrangements to collect imaging information. Due to exceptionally-low signal/noise ratios, progress in the field has been slow compared with other wavelengths. Despite the difficulties, this young field of astronomy is well established now, in particular due to advances made by NASA's Compton Gamma-Ray Observatory in the 90ies. The most important achievements on extra-solar gamma-ray lines so far concern: short-lived radioactivities that have been detected in a couple of supernovae (56Co and 57Co in SN1987A, 44Ti in Cas-A), the diffuse glow of long-lived 26Al and 60Fe that that has been mapped along the entire plane of the Galaxy, and last but not least, positron annihilation that has been observed in the inner Galaxy since the 70ies. I will review past and future developments in the field, in the light of recent results from ESA's INTEGRAL satellite, which is in operation since early 2003.

Prof. Ugo Gastaldi, Laboratori Nazionali di Legnaro, Italy - PVLAS, an experiment to probe vacuum with polarized light: results and prospects

The PVLAS experiment operates at LNL an ellipsometer (with a 6m long vertical Fabry-Perot cavity which embraces a rotating 5.5 Tesla superconducting dipole magnet) that can measure ellipticity and rotation induced by the magnetic field onto linearly polarized laser light. The sensitivity of the instrument is of the order of 10^-7rad sqrtHz^-1 with infrared light stored in the Fabry-Perot. Measurements have been made with infrared laser light until 2004, and with green light during 2005. With a residual pressure less than 10^-7mbar the apparatus gives both ellipticity and rotation signals at the 10^-7rad level. These signals can be interpreted as being generated largely by vacuum ellipticity and dichroism induced by the transverse magnetic field. If this interpretation is correct, a tool has become available to characterize physical properties of vacuum as if it were an ordinary transparent medium. A microscopic effect responsible for the induced dichroism could be the existence of ultralight spin zero bosons with masses of the order of 10^-3 eV, that would couple to two photons and would be created in the experiment by interactions of photons of the laser beam with virtual photons of the magnetic field. The coupling gm?? of these bosons to two photons would be of the order of 10^-6 GeV . Axions and dilatons are respectively pseudoscalar and scalar bosons that could exist with masses of the order of 10^-3 eV and with extremely weak couplings to ordinary matter.

Prof. Claus Rolfs, Ruhr Universität Bochum, Germany - Fusion reactions in stars

Fusion reactions play a key role in stars for the understanding of their energy production, evolution and neutrino emission. The experimental approaches in the study of some key reactions are presented. An important aspect are hereby the effects of electron screening, which increase the fusion cross sections. The fusion reaction d(d,p)t was recently studied in deuterated metals and insulators, i.e. for 58 samples across the periodic table, where a dramatic increase was observed for the metals. An explanation of the data is presented and possible future applications are discussed.

Prof. Valery Nesvizhevsky, Institut Laue-Langevin de Grenoble - The project GRANIT to measure the resonance transitions between the gravitationally bound quantum states of neutrons

The gravitationally bound quantum states of matter were observed for the first time due to unique properties of ultracold neutrons. Some parameters of the lowest quantum states of neutrons were measured in recent experiments in so-called integral and differential measuring modes. We are going to improve considerably the accuracy of these experiments using resonance transitions between the gravitationally bound quantum states of neutrons. In addition to the obvious interest to study this phenomenon itself, this experiment could be useful for different fields of physics such as, for instance, the search for spin-independent or spin-dependent short-range fundamental forces, the quantum-mechanical localization or the loss of quantum coherence. We will discuss different methodical approaches to measure the resonance transitions and the challeges and constrains in such an experiment.

Andrée Robichaud-Véronneau, Université de Genève - ZEUS: A detector for HERA

HERA is the first lepton-proton collider in the world where a center of mass energy of 318 GeV is reached. Since 1992, the ZEUS detector is gating luminosity from it to probe QCD and look for exotic phenomena of fundamental particle physics. A history and overview of the detector and collider will be presented as well as important physics contributions made by the ZEUS experiment to the understanding of our world.

Dr Albert De Roeck, CERN - CMS Physics Performance

An overview will be given of the physics capabilities of the CMS detector at the LHC. CMS is now completing its Physics Technical Design reports, summarizing the expected detector performance in a first volume and the physics reach with up to 30 fb-1 in the second volume. Results on the performance of the CMS detector as obtained from detailed simulations are presented for realistic operating conditions, and validated where possible against test beam and cosmic ray data. Procedures to measure the performance from early LHC data wil be described. Finally, a selected number of results from new physics studies will be presented.

Dr. David Lhuillier, CEA, Saclay - Violation de parité en diffusion Moller et tests précis du modèle standard à basse énergie

Les mesures du courant faible neutre à basse énergie, loin du pôle du Z⁰, permettent de tester le secteur électrofaible du modèle standard d’une manière complémentaire aux collisionneurs de haute énergie. La très faible intensité du courant neutre aux cinématiques étudiées est compensée par une très grande précision de mesure qui permet de tester indirectement l’existence d’une nouvelle physique jusqu’à l’échelle du TeV.
L’essentiel de l’exposé sera consacré à la présentation de l’expérience E158 qui isole la contribution du courant faible dans la diffusion Møller (e^-e^- -> e^-e^-) par l’intermédiaire de la violation de parité dans ce processus. L’impulsion transférée lors de la réaction est trois ordres de grandeur plus petite que la masse du Z⁰ et la violation de parité se traduit par une asymétrie de taux de comptage de l’ordre de 10^-7, mesurée à 10^-8 près. Une telle précision est rendue possible par les récents développements technologiques des sources d’électrons polarisés.
Le résultat de E158 sera présenté dans le contexte des autres mesures publiées (violation de parité dans les atomes et diffusion de neutrinos) et je discuterai son impact sur l’existence de quelques scénarii de nouvelle physique.
La fin de l’exposé sera consacrée aux perspectives d’expériences de violation de parité ouvertes par l’amélioration constante de la précision de mesure des asymétries.

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Semestre d'Hiver 2005-2006

Dr Mathieu Ribordy, Université de Mons-Hainaut, Belgique - Astronomie neutrino au Pôle Sud

Nous allons discuter du détecteur AMANDA enterré dans les profondeurs du Pôle Sud et de résultats récents obtenus dans la recherche de sources astrophysiques de neutrinos de haute énergie. Les limites actuelles au flux diffus, de plus en plus contraignantes, sont proches de la limite supérieure de Waxman-Bahcall. La sensibilité à la recherche de sources ponctuelles a atteint le niveau requis pour détecter des objets tels que Mrk501, en supposant un flux de neutrinos d'intensité comparable au flux de gamma, au-delà de ~1 TeV. Le successeur de AMANDA est le télescope IceCube dont le déploiement a commencé cette année. Il occupera à terme un volume de 1km³ et mènera à un gain de sensibilité de près de deux ordres de grandeurs. Aussi, des opportunités pour tester de la nouvelle physique s'offriront: entre autres, la recherche de matière obscure ou la mise en évidence de nouvelles sources d'oscillations de neutrinos par l'exploitation de l'incomparable statistique de neutrinos atmosphériques de haute énergie. fichier .pdf de la présentation

Prof. Peter Weilhammer, Université et INFN Perugia - CVD Diamond Radiation Sensors For Application In Very High Radiation Environments

After an introduction into the basic properties and operating principles of CVD diamond radiation sensor material, measurements of charge carrier collection and leakage currents in single crystal and polycrystalline CVD diamonds will be presented. Results from measurements of the effective mobilities and carrier lifetime of electrons and holes, using the Transient Current Technique (TCT), will be shown. Radiation hardness of CVD polycrystalline diamonds will be discussed. A summary of radiation hardness measurements, carried out over several years, will be presented for polycrystalline material. Performance of diamond tracking detectors will be discussed. Preliminary results from tests on a full ATLAS pixel module, equipped with 16 radiation hard readout chips, will be shown. Finally present and future application of diamond detectors in beam monitoring and diagnostics at different accelerators are discussed. fichier .pdf de la présentation

Prof. Sonia Kabana, University of Nantes and Subatech, France - The search for the QCD phase transition

We review the experimental efforts to reproduce and measure in the laboratory the QCD phase transition from deconfined quarks and gluons to hadrons, colliding heavy ions for example gold on gold, at energies high enough to cross the critical energy density of about 1 GeV/fm3, predicted by lattice QCD.

We will discuss our present understanding of the results acquired at BNL AGS, CERN SPS, and recently at BNL RHIC. In particular we will address the 'discovery of a new state of matter..' announced at CERN (2000) and at RHIC (2005), as well as the open questions reflecting into new experiments at the CERN LHC and at the GSI FAIR.

Dr Luis Mario Fraile, CERN - Highlights from the ISOLDE facility

The ISOLDE online mass separator located at CERN provides a wide variety of radioactive ion beams for research on nuclear physics, nuclear astrophysics, fundamental interactions, condensed matter and others fields. The facility maintains an extensive physics-driven target and ion source development programme, which has helped ISOLDE keep its international status throughout decades. The low-energy programme is complemented by research performed with accelerated radioactive ion beams. This has been made possible by the REX-ISOLDE post-accelerator, which has opened up new fields of study by means of transfer reactions and Coulomb excitation of exotic nuclei.

ISOLDE is integrated in the European research structure through the EURONS (EUROpean Nuclear Structure) infrastructure initiative, and plays a key role in the design study of the future European third-generation ISOL radioactive ion beam facility, EURISOL. In this context, the presentation will highlight recent ISOLDE scientific achievements and technical developments together with an outlook to future upgrades. fichier .pdf de la présentation

Prof. Krzysztof Piotrzkowski, Université Catholique de Louvain, Belgique - High energy photon interactions at the LHC

A significant fraction of proton collisions at the LHC will involve photon interactions at the energies above the electroweak scale. Experimental prospects for studying such interactions at the LHC will be presented, including the rôle of the forward proton detectors in tagging and reconstruction of photon induced events. Physics scope of high-energy photon-photon fusion and photon-proton interactions at the LHC will be discussed, focusing in particular on the two-photon production of W and Z pairs, and the associated photo-production of W and Higgs bosons. Finally, importance of studying the exclusive production of lepton pairs for searches beyond the Standard Model and for calibrating detectors will be addressed.

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Last updated: 9 mars 2010, Blanchard Catherine