| |
Séminaires
de physique corpusculaire
Les
séminaires du DPNC ont lieu les mercredis à 17.00 heures (chaques
deux semaines) dans l'auditoire Stückelberg, Ecole de physique, 24, quai
Ernest-Ansermet, Genève.
|
Retour
Semestre d'été
2001-2002
Prof.
Ralph Eichler:
The Particle Physics Programm at the Paul Scherrer Institut
Precision experiments
using high intensity pion, muon or neutron beams are sensitive to new forces or
particles. Three examples will be given: i) pion beta decay, ii) rare muon decays
and iii) search for an electric dipole moment of the neutron.
Dr. Xin Wu - U. Geneva:
CDF Startup
The RunII of the Fermilab Tevatron Collider began in 2001, after
extensive upgrades to both the machine and the CDF and D0 detectors.
An overview to the CDF detector upgrades and performeance will be
described, in particular the unique L2 impact parameter track trigger
(SVT). The current data-taking status, as well as a fisrt glimpse of CDF
data will be presented.
Dr. Philippe Chomaz - GANIL:
Atomic Nuclei in 2002: Surprises, discoveries and evolutions
In this talk we will show how the study of nuclei under
extreme conditions have changed our understanding of
atomic nuclei. Indeed in the past 10 years unexpected
results and important discoveries have shown how far
nuclear models are from a realistic picture.
Hot nuclei have renewed our understanding of phase
transitions in finite systems in particular with the
observation of negative heat capacities. This anomalous
behavior has now been observed in other mesoscopic
systems such as metallic cluster.
Exotic nuclei have contradicted the paradigm of the
nucleus as a homogeneous quantum drop of nucleons.
The discovery of halo and molecular nuclei as well as
the observation of the disappearance of magic number
in neutron rich regions of the nuclear chart are some
example of the actual "nuclear structure crisis".
Dr. Christian Spiering - DESY-Zeuthen: High energy neutrino astronomy
- status and prospects
After a long period
of development, high energy neutrino astrophysics is approaching a level of sensitivity
which reaches below the upper bounds on extraterrestrial neutrino fluxes derived
from the observed fluxes of cosmic rays and gamma rays. The day when first positive
observations will start to populate the neutrino sky could therefore be close.
The talk reviews physics goals and experimental status of high energy neutrino
astronomy, with emphasis on results from the Amanda neutrino telescope at the
South Pole.
Dr. Monika Grothe - CERN:
Mixing in the D0 system at BaBar
Mixing in the D0 system may provide a sensitive probe for new physics
beyond the Standard Model (SM). The SM predictions are small (<10-3)
for the mixing parameters x, y which, in the absence of CP-violation,
measure the difference in mass (x = DeltaMass/Gamma) and lifetime
(y = DeltaGamma/2Gamma) of the CP-eigenstates in the D0 system. New
physics may significantly enhance x while y is expected to be dominated
by SM processes.
The BaBar detector at the e+e- storage ring PEP-II provides the
opportunity of studying charm decays with unprecedented statistics and
purities. Two experimental methods will be described in detail: The
determination of y from the D0 lifetime difference in the decays K-pi+
and K-K+, pi-pi+, and the extraction of y, x^2 and the wrong-sign
(D0 ->K+pi-) decay rate from the time evolution of the D0 decay rate.
Preliminary BaBar results for y and the wrong-sign decay rate will be
presented.
Dr. Volker Beckmann - Observatoire de Genève:
Blazars - The extreme Active Galaxies
Blazars mark the extreme end of the AGN (Active Galactic Nuclei)
population. These galaxies are thought to host a supper massive black
hole. Accretion onto this mass forms a disk of matter around the central
engine. This process is accompagnied by forming a jet perpendicular to the
disk, which transports electrons and/or positrons at relativistic speed
away from the black hole. In the case of Blazars we look directly into
this jet. The interaction of the particles which form the jet and the
magnetic field surrounding it, leads to synchrotron radiation, and photons
are up-scattered by relativistic electrons in inverse Compton processes.
This leads to the observed properties of these AGNs: high variability,
strong polarization, non-thermal emission, and a characteristic spectral
energy distribution. The violent processes in the jet make Blazars
observable up to the TeV domain.
This talk will focus on the appearance of Blazars and especially what is
observable at high energies.
Prof. Prof. Jean-Luc Vuilleumier - U.Neuchâtel:
Neutrino properties from experiments at low energy
The study of solar and atmospheric neutrinos has brought new insight on
neutrino properties. Neutrinos have been shown to oscillate, and thus
have masses. But the mass scale is still unknown. Next generation
searches for neutrinoless double beta decay may give an answer. Some
projects will be discussed. Also neutrinos may have magnetic moments,
which may have an impact on oscillation patterns. Searches for magnetic
moments with sources or at nuclear reactors will be presented.
Dr. K. Ragan - McGill University:
Ground-based gamma-ray astrophysics
Some of the most enigmatic phenomena in the Universe -- black-hole driven
Active Galactic Nuclei, pulsar-driven Supernova Remnants, and perhaps
even Gamma-Ray Bursts -- are now known to be strong gamma-ray emitters.
Many have been seen and studied from orbiting satellite-based detectors,
and a few from the ground. Unfortunately, these two techniques have, until
now, left an 'unexplored window' in gamma-ray energy between approximately
10 GeV and 250 GeV. There is good reason to expect that this energy
range is crucial to understanding these sources and the propagation of
gamma-rays across the Universe. A number of new techniques and detectors
are addressing this energy range; this talk will briefly introduce the
scientific motivation for these detectors and talk about the different
experimental approaches.
Retour
Semestre d'hiver
2001-2002
Dr. Pierre Antilogus, IPN - Lyon: La constante cosmologique : mesure
et perspectives
Les SuperNovae de
type Ia (SN Ia) ont fourni la 1ère indication tangible de la présence d'une constante
cosmologique non nulle. Les SNIa vont être amenées à jouer un rôle clef dans la
mesure de l'énergie du vide ou plus généralement dans l'étude de l'Energie Noire.
Au cours de ce séminaire, après avoir introduit le contexte scientifique, l'état
actuel de la mesure de la constante cosmologique sera revu. Les perspectives d'une
cosmologie de précision à l'aide des SN Ia sera présenté. Les programmes "nearby
SuperNova Factory" (SNFactory) et "SuperNova Accelerating Probe satelite" (SNAP)
seront introduits.
Dr. J. Alcaraz, CIEMAT/CERN: What have we learned from LEP2?
In this talk we will
try to discuss LEP2 results from a non-standard point of view. It is well known
that LEP collaborations have searched for the Higgs particle and for new physis
beyond the Standard Model. Precise measurements of the W mass and the triple gauge
coupling structure predicted by the theory are also underway. What is not so well
known is that LEP2 physics presents many unique features when compared to LEP1
and e+e- interactions at lower energies. This new high energy domain is somehow
comparable to the electroweak environment that will be found a future e+e- colliders.
Dr. J. Ocariz, LPNHE Paris VI-VII: Recent results on CP violation from
BaBar
Following the spectacular
turn-on of both the SLAC and KEK B factories, results from BaBar and Belle on
CP violation have recently been published. I will review the analysis of time-dependent
CP violating asymmetries in BaBar, together with a few other topics on B physics,
and discuss future prospects.
Dr. A. Ealet, CPPM-Marseille: Vers une mesure precise de l'energie noire:
Le projet SNAP(SuperNova Acceleration Probe)
Les supernovae de
type Ia (Sn Ia) sont un outil simple et direct pour connaitre l'histoire de notre
univers. Apres un rappel rapide du contexte scientifique, nous examinerons comment
les supernovae peuvent donner des mesures de precision et montrerons qu'un echantillon
important de SN avec des systematics bien controlees permet, au dela de la mesure
precise de la constante cosmologique, une determination sans ambiguite de la nature
de l'energie noire. Le projet de satellite SNAP est concu et dedie pour repondre
a cette attente. Avec quelques milliers de SN Ia par an, il permettra de separer
les modeles d'energie noire par la mesure du parametre w avec une precision meilleure
que 0.05.
Dr.
A.Stocchi LAL-Orsay/CERN
10
Years of B Physics at LEP
In this seminar I'll
show how, in the past 10 years, some measurements and theoretical results, have
improved our knowledge of the Flavour Sector of the Standard Model. I'll put more
emphasis in the central role played by the LEP experiments in most of these measurements
and their impact in the determination of the Unitarity Triangle parameters.
Dr.
P. Jarron (CERN) , Dr. M. Winter (IReS-Strasbourg)
New
developments in silicon detectors
In this seminar two
projects of new pixel silicon for charged particle tracking will presented: the
deposition of hydrogenated amorphous silicon above integrated circuits and the
Monolithic Active Pixel Sensors
Hydrogenated amorphous silicon - a-Si:H - has been considered for a long time
as a potential semiconductor material candidate to build low cost radiation sensors.
Poor charge collection and insufficient signal to noise ratio have been the main
issues preventing successful results. The deposition of hydrogenated amorphous
silicon films above the readout integrated circuits is an attractive approach
to overcome these issues and could allow to build radiation hard and low cost
pixel detectors for tracking applications. Properties and fabrication of thin
film a-Si:H detector will be discussed, and very preliminary results of a-Si:H
deposition on ASICs will be presented.
Monolithic Active Pixel Sensors are new type of semi-conducting pixel which is
expected to combine specific advantages of Charged Coupled Devices and Hybrid
Pixel Sensors in a fully integrated architecture, where the read-out micro-circuits
are implemented on the sensor substrate. Tests of the first prototypes demonstrate
that this technology allows to detect m.i.p.s with high performances and is already
adapted to rather sizeable radiation fluxes. The main results obtained will be
discussed and the current and planned developments will be presented.
Retour
Last updated: 23 April 2002, Eduardo Cortina
