Nov 30 : Dr Marco Fernandez Garcia - IFCA, Spain -
Access to the talk
Title : 3D laser characterization of semiconductor devices
Abstract : The time-resolved analysis of the laser-induced
currents on semiconductor detectors has been proven to be a chief
and versatile tool for the understanding of the effects produced by
the ionising radiation on such devices. So far, all these methods
and techniques, known as Transient Current Techniques (TCT), are based
on the single-photon absorption process where just one photon is required
to create an electron-hole pair. We have developed a new TCT system
based on a simultaneous Two-Photo-Absorption (TPA) for the creation
of an electron-hole pair. This innovative TPA-TCT technique makes
an important breakthrough with respect to the current state-of-the-art
since it allows for the laser-induced generation of charge carriers
on a very localised micrometric-scale voxel; opening a broad field
of opportunities for the study of the current new generation of small-pixel
devices where spatial resolution is a mandatory. The improved spatial
resolution of this new measurement technique has allowed to resolve
features like the Deep Implant of an HVCMOS, distinguish between drift
and diffusion regions and calculate the effective doping concentration
of the bulk. The technique can be used for 3D mapping of key properties
of a detector, like the collected charge or electric field.
Dec 07 : Dr Lino Miceli - CAPP & KAIST, South Korea - Access
to the talk
Title : Search for Relic Axions with the CAST Magnet at CERN
Abstract : There has been an increasing interest in
searches for the axion, particularly over the past few years. Technology
advances, and the development of new ideas, might in fact soon lead
to experiments with unprecedented sensitivity over a mass range, roughly
1 to 100 μeV, where a discovery could solve two outstanding issues
of modern physics, namely the so-called Strong CP problem and the
nature of cold dark matter.
The IBS Center for Axion and Precision Physics Research (CAPP/IBS)[1],
based at the Korea Advanced Institute of Science and Technology (KAIST),
was established with the goal to address the Strong CP problem, the
axion resolution of it, and the proton electric dipole moment value.
As part of its international collaborative efforts, the CAPP leads
an experiment at CERN, the CAST-CAPP/IBS project, within the CERN
Axion Solar Telescope (CAST) [2] collaboration.
Axions can couple to two photons in the presence of a strong magnetic
field, B, as expressed by the Lagrangian term L= -gaγγ
a(t)E(t)∙B . Where gaγγ is the coupling constant, a(t)
is the axion field, and E(t) the electric field associated with the
outgoing photon in this Primakov-like process. This coupling is the
base of the CAPP axion search, in the version proposed by Sikivie
[3] where a microwave cavity immersed in a strong magnetic field is
tuned to resonate at the frequency of the axion mass (haloscope).
In the CAST-CAPP/IBS project, based on ideas suggested a few years
ago [4], rectangular cavities are inserted in the 9T CAST dipole magnet,
an LHC prototype, at CERN. The status and expected sensitivity of
this experiment will be presented.
Dec 14 : Dr Federico Sanchez, IFAE Barcelona, Spain - Access
to the talk
Title : Precision oscillation neutrino experiments, nuclear physics
and the need of near detectors
Abstract : Neutrino oscillation physics have entered
the era of precision physics. Next decade might see the first measurement
of CP violation in neutrinos. But, this precision experiments requires
to understand two main elements: neutrino flux and neutrino-Nucleus
cross-sections. Near detectors, located few hundred meters from the
neutrino production points, are in charge of these tasks. But, this
enterprise is not trivial, our knowledge of neutrino-nucleus interaction
model is lacking the precision and understanding of other fields of
particle physics. Modern neutrino oscillation experiments focuses
most of their efforts in this specific task. We will discuss neutrino
oscillation experiment methodology, its challenges in the boundary
between particle and nuclear physics and the need of near detectors
in running and future experiments.
Semestre
de Printemps 2016
March 2 : Dr Teng Jian Khoo, Université de Genève-
Access to the talk
Title : Event reconstruction in SUSY searches at ATLAS and the
LHC
Abstract: The LHC experiments have since 2010 dramatically
transformed the landscape of supersymmetry, providing ever tighter
constraints on how supersymmetric theories could be realised in nature.
Central to most SUSY searches is the missing transverse momentum signature,
signifying the presence of undetected particles such as stable neutralinos
produced in cascade decays. This seminar will describe advances in
the measurement of missing transverse momentum in ATLAS, and how we
derive and employ transverse mass variables in the quest for supersymmetry
at the LHC.
March 16 : Dr Stephan Zimmer, Université de Genève -
Access to the talk
Title : Galaxy Clusters as unlike Cold Dark Matter candidates
harboring complex astrophysics - 7+ years of Fermi-LAT observations
and still no firm detection
Abstract: Galaxy clusters are the most massive virialized
systems known in the Universe and are believed to have formed through
large scale structure formation. They host relativistic cosmic-ray
(CR) populations and are gravitationally bound by large amounts of
Dark Matter (DM), both providing conditions in which high-energy gamma
rays may be produced either via CR interactions with the intracluster
medium or through the annihilation or decay of DM particles.
Prior to the launch of the Fermi satellite, predictions were optimistic
that these sources would be established as gamma-ray-bright objects
by observations through its prime instrument, the Large Area Telescope
(LAT). Yet, despite numerous efforts, even a single firm cluster detection
is still pending.
In my talk I will provide an overview and discuss recent studies carried
out by the LAT collaboration aiming to discover these missing gamma
rays and discuss detection prospects with planned observatories such
as CTA and DAMPE.
April 6 : Dr Pier-Olivier Deviveiros, CERN - Access
to the talk
Title : Tau Leptons at ATLAS: Reconstruction & Physics
Abstract: Tau leptons play a significant role in the ATLAS physics
program. As the heaviest leptons, they offer the most sensitive probe
into the properties of leptonic Higgs couplings. Additionally, they
offer unique sensitivity to beyond the Standard Model physics scenarios
where they are often produced preferentially. From the first observation
of hadronically-decaying taus in W decays in 2010, to the recent evidence
for Higgs decays to leptons, a lot of progress has been made in the
reconstruction of tau leptons at ATLAS. In this seminar, a summary
of the tau reconstruction, calibration and identification algorithms
at ATLAS will be shown. Additionally, a review of the most recent
ATLAS physics results in final states with hadronically-decaying tau
leptons will be presented.
April 20: Dr Patrick Czodrowski, University of Alberta - Access
to the talk
Title : Searches for strong gravity signatures produced in proton-proton
collisions using the ATLAS detector at the CERN Large Hadron Collider
Abstract : Searches for new physics in using data from proton-proton
collisions at √s = 8 TeV and 13 TeV taken at the CERN Large Hadron
Collider with the ATLAS detector were conducted. The presented searches
focus on signatures of new physics models of strong gravity that hypothesize
additional space-time dimensions, as for example black holes and string-balls.
After a summary of current results an outlook on the future search
efforts by the ATLAS collaboration in this physics domain is given.
May 4 : Dr Elisabetta Pianori, University of Warwick - Access
to the talk
Title : ATLAS and CMS Higgs coupling combination
Abstract : I will present the first combined ATLAS+CMS measurement
of the Higgs boson production and decay rate based on the 5/fb of
7 TeV and 20/fb of 8 TeV data. Constraints on the Higgs boson’s couplings
to other SM particles are presented as well. This is the most precise
and comprehensive experimental results to date. I will also highlight
how these measurements constrain the existence of new physics, and
discuss the prospects for Higgs boson measurements and their interpretations
in Run2.
Semestre d'automne 2015
Sept 23 : Dr Roland Horlsberger - PSI
Title : The CMS pixel detector in LS1: a surprising story has
a good ending - Access to
the talk
Abstract: The CMS pixel detector has proven to be a crucial
in the track reconstruction of CMS. The installation of a new smaller
radius beam pipe in LS1 required the removal in Spring 2013 and storage
outside the CMS experiment. This has not been without surprises before
its re-installation in Fall 2014 into CMS for Run2. The talk describes
the detailed chain of events that required a successful repair of
the barrel pixel prior to its re-installation into CMS. The talk will
also briefly describe the status of the ongoing Phase I Pixel Upgrade
that is planned to installed in 2017.
Sept 25 : Prof. Zhen CAO - Institute of High Energy Physics, Beijing
Title: A multi-purpose Cosmic Ray Experiment:
The LHASSO Project
Abstract : In 21st century, one of the fundamental scientific problems
is the origin of the cosmic rays which were discovered 103 years ago.
One of successful approaches is the VHE gamma ray astronomy that was
started with the discovery of the Crab Nebula as a source of the gamma
rays above 1 TeV at 1989. More than 150 VHE gamma ray sources are
discovered, mainly by using the pointing Cherenkov telescopes such
as HESS, MAGIC and VERITAS. To keep the momentum of the discovery
power, a full sky survey with wide field of view and full duty cycle
is necessary. Struggling on developing a right survey technology,
the Chinese group together with its Italian and Japanese collaborators
has successfully carried out two experiments, ARGO-YBJ and ASγ in
last 25 years and has proposed the LHAASO project now. In this presentation,
the scientific achievements of ARGO-YBJ will be cited as indications
of what will be possibly achieved by LHAASO that is a factor of 30
more sensitive at low energies and 300 more sensitive at high energies
than ARGO-YBJ. Simultaneously, LHAASO will significantly boost the
performance of cosmic ray measurements in the energy region of “knees”.
The scientific prospects, detector performance and prototyping status
will be summarized.
Oct 14: Dr Olaf NACKENHORST, Université de Genève, DPNC
Title: Search for the Higgs boson produced in
association with top quark pairs at 8 TeV with the ATLAS detector
using the Matrix Element Method -
Access to the talk
Abstract : After the discovery of a Higgs boson in bosonic decays,
it is important to confirm this particle in fermionic decays in order
to gain more confidence in the Standard Model (SM) Higgs boson hypothesis
of the observation.
The production of the Higgs boson in association with a pair of top
quarks (ttH), is one of the four main production mechanisms of the
Higgs boson predicted by the SM.
Despite the fact that many searches for this production mechanism
have been performed during Run I of the LHC, it has not yet been observed.
Such an observation would not only verify the coupling of the Higgs
boson to fermions, but would also allow for the most direct determination
of the top quark Yukawa coupling, which is an important parameter
of the SM.
The presented search is designed for the b-quark pair decay mode of
the Higgs boson and makes use the Matrix Element Method (MEM) to better
distinguish the signal from its main and irreducible background tt+bb.
The MEM uses the theoretical description of a process in order to
assign a probability weight to each observed event.
This probability reflects how likely it is that the observed event
is consistent with a certain hypothesis.
Powerful discriminants can be constructed from the signal and background
probabilities to significantly enhance the search sensitivity.
Oct 16: Dr Arnaud JOLIVET - Procédure de nomination
Title:The role of brain energetics in information
processing and immune surveillance
Abstract :
The nervous system consumes a disproportionate fraction of the resting
body’s energy production: in humans the brain is only 2% of the body’s
mass, yet it uses ~20% of the oxygen consumed by the body. Expansion
in the size of the brain relative to the body and an increase in the
number of connections between neurons during evolution underpin our
cognitive powers and are responsible for our brains’ high metabolic
rate. The molecules at the center of cellular energy metabolism also
act as signals to other cells and constitute an important communication
pathway, coordinating for instance the immune surveillance of the
brain. Despite the significance of energy consumption in the nervous
system, how energy constrains and shapes brain function is often underappreciated.
I will illustrate the importance of brain energetics and metabolism
with two examples from my recent work. First, I will show how the
brain trades information for energy savings in the visual pathway.
Indeed, a significant fraction of the information those neurons could
transmit in theory is not passed on to the next step in the visual
processing hierarchy. I will discuss how this can be explained by
considerations of energetic optimality. Second, I will show how adenosine
triphosphate, the energy currency of cells, is critical in regulating
immune surveillance of the brain by a specialised population of brain
immune cells. I will also discuss a new mechanism that we recently
identified, which plays a key role in regulating the patrolling of
brain tissue by these cells. I will conclude by discussing future
research directions in brain energetics.
Nov 4 : Dr Pierre BARRILLON, LAL, CNRS, Paris
Title: EUSO-BALLOON, the story of three adventurous
years
Abstract : The night of the 24th of August 2014, EUSO-BALLOON instrument
took off from the stratospheric balloons launching base of Timmins
in Ontario (Canada). Supported by a 400000 m3 helium balloon, it flew
for about 5 hours at an altitude of 38 km over forests. In total,
around 100 Go of data were acquired. They are used to better know
the UV background from sky and earth as well as the infra-red emission
of the clouds.
This flight is the outcome of almost 3 years of work of a scientific
and technical collaboration involving 50 people and supported by the
CNES balloon division.
This seminar will relate the adventure of this project from the kick
off meeting of the 14th of September 2011 until the recent results
of the data analysis presented at ICRC conference.
Nov 11 : Dr Rolf BUEHLER, DESY
Title: The Universe observed in Gamma-rays
Abstract : Astronomical sources are able to accelerate particles to
energies far beyond what accelerators at Earth can do. The study of
these astrophysical accelerators takes one to some of the most extreme
places in the Universe, such as Super Massive Black Holes, Neutron
Stars or Super Novae explosions. The particle acceleration in these
sources are best studied in gamma-rays. In this presentation I will
give a tour through the gamma-ray sky and discuss the acceleration
and emission mechanisms at work in high-energy sources.
Semestre
de Printemps 2015
| Date |
Conférencier |
Titre du séminaire et Annonce |
| 14 Jan. |
Dr Avishek Chatterjee
Université de Genève, DPNC |
Fast Ion Instability at CESR-TA |
| 04 Mar. |
Dr Enrico Jr. Schioppa
Université de Genève, DPNC |
The color of X-rays |
| 01 Apr. |
Dr Steven Schramm
Université de Genève, DPNC |
Searching for Dark Matter at ATLAS  |
| 15 Apr. |
Dr Andrea Coccaro,
Université de Genève, DPNC |
Looking for a hidden sector in exotic Higgs
boson decays with the ATLAS experiment |
| 06 May |
Dr Chiara Casella,
ETHZ |
The SAFIR project - Challenges of a novel
detector for fast hybrid PET/MR imaging |
| 13 May |
Dr Heather Gray,
CERN |
The Art of the Impossible: Probing challenging
Higgs channels at the LHC |
| 27 May |
Dr Felix Sefkow,
DESY |
Imaging calorimeters for particle flow reconstruction
|
| 24 Jun. |
Prof. Mark Hartz,
IPMU, University of Tokyo |
nuPRISM: A Novel Experiment for Studying Neutrino-Nucleus
Interactions |
Jan. 14: Dr Avishek Chatterjee, University of Geneva, DPNC
Title: Fast Ion Instability at CESR-TA - Access
to the talk
Abstract:Fast Ion Instability can lead to deterioration
of an electron beam (increasing emittance and instability of a train
of bunches) in storage rings and linacs. An overview of the study
done at at the Cornell Electron Storage Ring Test Accelerator using
a 2.1 GeV low emittance beam will be presented. As the source of ions
is residual gas, measurements are conducted at various pressures,
including nominal vacuum as well as injected gas (Ar, Kr). We experiment
with mitigation techniques, including changing the bunch pattern to
have mini-trains instead of one long train, as well as increasing
the initial vertical emittance of the beam. We also check to ensure
that ion-trapping is not a substantial effect in our measurements.
We measure turn-by-turn vertical bunch size and position, as well
as the multi-bunch power spectrum. Our measurements confirm fast ion
instability under all vacuum conditions. A detailed simulation is
then used to compare theory with observations. Since Fast Ion Instability
is likely to be a significant effect for beam conditions expected
at CLIC and ILC, such studies are of great importance for a deeper
understanding of design considerations for future accelerators.
Mar 04: Dr Enrico Jr. Schioppa, University of Geneva, DPNC
Title: The color of X-rays - Access
to the talk
Abstract: We all are familiar with the definition
of colors as related to the energy of visible light photons. What
is the best way we can define colors also in other ranges of the electromagnetic
spectrum?
The X-ray range is particularly interesting because X-rays are widely
used for non-invasive imaging. The fact that radiography has always
been a greyscale imaging technique is related to limitations on the
X-ray detector technology: conventional detectors for imaging applications
cannot measure energy, but only radiation intensity. The interest
towards novel detectors that are capable of achieving spectral resolution
together with spacial resolution is very high, because, as it turns
out for X-rays, colors can be defined in terms of the materials contained
in the imaged sample. This means that, among other advantages (such
as dose reduction), spectral X-ray imaging would allow for direct
material separation capability.
It will be discussed how the study of the charge transport properties
in the sensor, together with an accurate calibration of individual
pixels, can lead to the full knowledge of the detector energy response
function. Furthermore, it will be shown how this information can be
exploited to achieve color (i.e. material resolved) and artifact-free
3D X-ray imaging.
Apr. 1st: Dr Steven Schramm, University of Geneva, DPNC
Title: Searching for Dark Matter at ATLAS - Access
to the talk
Abstract: Despite decades of studies, the nature of
Dark Matter remains one of the largest open questions in physics.
In particular, it is not known if elusive Dark Matter particles can
interact with normal matter. If such an interaction exists, and if
the Dark Matter particles are not too massive, then they can be produced
in high-energy collisions at the LHC. Collisions producing only Dark
Matter particles are invisible in ATLAS, as the Dark matter particles
escape the detector without interacting. Instead, searches focus on
events where invisible Dark Matter particles are balanced by visible
objects.
One particularly sensitive topology at the LHC is where the visible
objects are jets (the hadronization of quarks or gluons). This specific
scenario is investigated, and results are interpreted in terms of
several different Dark Matter models. The expected sensitivity to
Dark Matter at an upgraded LHC is also briefly discussed.
Apr. 15: Dr Andrea Coccaro, University of Geneva, DPNC
Title: Looking for a hidden sector in exotic
Higgs boson decays with the ATLAS experiment - Access
to the talk
Abstract: The nature of dark matter is one of the most
intriguing questions in particle physics. Dark matter can be postulated
to be part of a hidden sector whose interactions with the visible
matter are not completely decoupled. The discovery of a fundamental
scalar particle compatible with the Higgs boson predicted by the Standard
Model paves the way for looking for dark matter with novel methods.
An overview of the searches looking for a hidden sector in exotic
Higgs decays within the ATLAS experiment is presented. Prospects for
searches with LHC data at a center-of-mass energy of 13 TeV are summarised
.
May 06: Dr Chiara Casella, ETHZ
Title: The SAFIR project - Challenges of a novel
detector for fast hybrid PET/MR imaging - Access
to the talk
Abstract: SAFIR (Small Animal Fast Insert for mRi) is
a novel, challenging project in instrumentation for Positron Emission
Tomography (PET), recently initiated at ETH Zurich, as a collaboration
between the Institute for Particle Physics (IPP) and the Institute
for Biomedical Engineering (IBT).
Goal of SAFIR is to design, build, and characterize an innovative
high counting rate PET insert for hybrid PET/MRI of small animals.
SAFIR will be designed to cope with ultra short PET scan durations,
of the order of a few seconds, at a high repetition rate, and simultaneously
with the magnetic resonance imaging (MRI). In the rapidly evolving
scenario of PET/MRI instrumentation, the peculiarity of SAFIR relies
on its excellent achievable temporal resolution, which will allow
for dynamic imaging on time scales precluded so far. To compensate
the statistics losses related with the acquisition duration, the PET
detector will be operated at high injected activities, up to ~ 500
MBq, one order of magnitude increase in the activities normally employed
in pre-clinical scanners. Severe requirements are then imposed on
the detector, which must be able to cope with such a high rate of
decays without suffering significantly of event losses, due either
to pileup or deadtime, and without being dominated by the randoms
contribution.
SAFIR relies on LYSO scintillating crystals readout by SiPM arrays.
Special emphasis right now is given to the choice of the readout solution.
At present, two existing ASICs, the TOFPET and the STiC chips, are
being investigated, with small scale setups tested with low activity
sources (in the laboratory) and with high activity phantoms (at Zurich
University hospital).
The SAFIR detector concept will be described, and its status in terms
of hardware characterization measurement and simulation results will
be summarized.
May 13: Dr Heather Gray, CERN
Title: The Art of the Impossible: Probing challenging
Higgs channels at the LHC - Access to the
talk
Abstract: Measurements of the Higgs coupling to top and bottom quarks
and the width of the Higgs were not thought to be possible at the
LHC Run 1. Yet, ATLAS and CMS have both produced promising results
for all these channels. I will highlight selected aspects of these
measurements to discuss what allowed ATLAS and CMS to probe the impossible.
May 27: Dr Felix Sefkow, DESY
Title: Imaging calorimeters for particle flow
reconstruction - Access to the talk
Abstract: In the past decade, advances in particle detection
technology and micro-electronics integration have led to the development
of highly granular calorimeters, able to produce detailed images of
electromagnetic and hadronic showers. These capabilities can be used
to reconstruct charged and neutral particles individually even in
the the dense environment of jets produced at present and future high
energy collider experiments. The talk will give an overview on the
concept, the technological developments and the results obtained in
test beam experiments.
June 24: Prof. Mark Harz, IPMU, University of Tokyo
Title: nuPRISM: A Novel Experiment for Studying
Neutrino-Nucleus Interactions
Abstract: Current and future neutrino oscillation experiments that
will search for CP violation and determine the mass hierarchy are
entering the era of precision measurements where uncertainties on
neutrino interaction models will limit experimental sensitivities.
Recent years have seen significant work to develop neutrino-nucleus
interaction models that account for all scattering processes in the
nuclear environment, but consistency between models and experimental
data is still elusive. The proposed nuPRISM experiment will take advantage
of the so-called off-axis effect in a neutrino beam from pion decays
to measure the properties of neutrino interactions on water with neutrino
spectra having peak energies ranging from 400-1200 MeV. By using measurements
over a range of energies, nuPRISM can predict observed final states
in neutrino oscillation measurements in a largely model independent
way. Conversely the data from nuPRISM can be used to over-constrain
neutrino interaction models with data from a single experiment. I
will describe the nuPRISM detector concept and its potential application
to oscillation experiments such as T2K and Hyper-K, as well as its
unique capabilities to make measurements of neutrino interaction cross
sections.
Semestre d'automne 2014
Sep 10: Dr Merlin Kole, KTH Stockholm
Title: Atmospheric Neutrons - a Background Study
for the X-ray Polarimeter PoGOLite
Abstract: Polarimetry remains a relatively unexplored
field of X- and gamma-ray astrophysics. The lack of polarimetric measurements
in this energy range is partly a result of the typically low signal
detection efficiencies of the detectors. A second reason, especially
relevant for balloon-borne detectors, is the high radiation environment
in which the measurements have to be performed. PoGOLite is a balloon-borne
hard X-ray polarimeter which performed its first scientific, near
circumpolar flight, during the summer of 2013. It is designed to measure
the polarisation of X-rays coming from astrophysical point sources,
such as the Crab nebula, using a segmented plastic scintillator array.
To reduce the measurement background PoGOLite employs several dedicated
background rejection systems. The background encountered during flight,
which is mostly a result of fast neutrons scattering in the plastic
scintillator array, remains however, significant. A detailed understanding
of the background is therefore required, including an understanding
of the variation of the background rate during the flight, and the
ability of such a backgrounds to induce a fake polarisation signal.
For this purpose, detailed Monte Carlo studies of the PoGOLite instrument
were performed. The high altitude atmospheric neutron environment,
responsible for the majority of the PoGOLite background, was furthermore
studied using a dedicated balloon-borne detector called PoGOLino.
This instrument uses a novel scintillator based technique to measure
the neutron flux. PoGOLino was launched from the Esrange Space Centre
in Northern Sweden in March 2013. The measurement results of this
detector will be discussed, together with a new model describing the
atmospheric neutron flux which was developed by members of the PoGOLite
collaboration. Finally the results of the PoGOLite flight of 2013
will be discussed and compared to predictions made using the performed
background study.
Sep 24: Dr Nicolo Cartiglia, INFN Torini
Title: Ultrafast silicon detector for Picosecond
Tracking
Abstract: In this seminar I will review the progress
towards the development of a new type of silicon detectors suited
for picosecond tracking, the so called Ultra-Fast Silicon Detectors
. UFSD are based on the concept of Low-Gain Avalanche Detectors, which
are silicon detectors with an internal multiplication mechanism so
that they exhibit a signal which is a factor of ~ 10 larger than standard
silicon detectors. This increased signal makes LGAD ideal for many
applications, ranging from experiments requiring very low material
budgets, to very high radiation environment, to applications that
need very precise timing.
I will report on first measurements and the plan for future productions.
Oct 8: Dr Nicola Pacifico, University of Bergen
Title: Weighting antimatter: The AEgIS experiment
Abstract: The AEgIS experiment at the CERN Antiproton Decelerator
aims at testing the weak equivalence principle by directly measuring
gravitational acceleration exerted by Earth on antihydrogen atoms.
The experiment will for the first time create a pulsed beam of antihydrogen
atoms that will then be selected through a moire deflectometer. Downstream
detection of the vertical acceleration is then performed through a
position sensitive detector, combining silicon strips emulsions and
scintillating fiber detectors.
We provide here an overview of the working principles of the experiment,
with an insight on the antihydrogen production and detection system.
Norway, with the University of Bergen and Oslo, is developing one
of the components of an hybrid annihilation detector. The sub-detector,
based on silicon microstrip sensors, will be the first application
of the technology to the detection of antihydrogen. In addition to
the challenges defined by this new type of measurement, the detector
will have to address technical constraints like cryogenic operation
and a reduced physical thickness (50 um). This seminar will cover
the aims and principles of the AEgIS experiment, with a final focus
on the development of the silicon annihilation detector at Bergen
and Oslo.
Oct
29 : Dr Alessandro Bravar, Université de Genève
Title: The Mu3e Experiment
Abstract: The Mu3e experiment will search for the lepton flavor violating
neutrinoless muon decay μ → e+e-e+ with a sensitivity of 10-16, a
four order of magnitude improvement over previous experiments, using
the world most intense muon beam at the Paul Scherrer Institute. This
decay is strongly suppressed in the Standard Model, whilst several
BSM models predict observable effects accessible to the new generation
of LFV experiments.
The search for the μ → e+e-e+ decay requires a large acceptance detector
capable of coping with rates of up to 2 x 10-9 stopped muons per second
with excellent momentum, spacial, and time resolution to suppress
backgrounds to below the 1016 level. The required Mu3e detector performance
is possible thanks to tracking detectors based on thin monolithic
active silicon pixel sensors (HV-MAPS) in conjunction with an innovative
tracking concept and very precise timing measurements using scintillating
fibers and tiles coupled to silicon photo-multipliers. The recently
approved Mu3e experiment is currently preparing for detector construction.
In this seminar I will breifly discuss the phenomenology of lepton
flavor violation and the various models suggesting sizable LFV effects
accessible to the next generation of muon experiments. I will overview
the status of current LFV searches. Then I'll discuss in detail the
principle and conceptual design of the Mu3e experiment and the experimental
challenges associated with this search. Finally I will illustrate
the various detector components and their expected performance.
Nov
19 : Dr Matt Noy, CERN
Title: TDCPix: A High Time Precision Pixel Chip
for the NA62 GigaTracker
Abstract: The TDCPix is a hybrid pixel detector readout ASIC designed
for the NA62 GigaTracker detector. The driving requirements are a
single-hit timing resolution better than 200ps RMS and a hit loss
of less than 1\% in the presence of a (highly non-uniform) beam rate
up to 80MHz/cm^2. This hit rate leads to an expected data rate at
the output of the chip which can reach 6Gb/s.
The TDCPix comprises an asynchronously operating pixel array with
1800 pixels organised as 40 columns of 45 pixels, each one 300 x 300
$\mu m^2$. The front end input stage has been optimised for a detector
capacitance of 250fF and the predicted ENC with the fully depleted
detector is better than 250$e^-$. The base-line detector is expected
to be a standard P-in-N planar pixel detector 200$\mu m$ thick, although
the front end remains programmable such that other detector technologies
may be evaluated. The pre-amplifier was designed with a peaking time
of 5ns to provide the required timing performance. Rather than distribute
a high precision reference signal to the pixel array,
the discriminated hit signals are driven to the end of column region
via dedicated transmission lines. There, each column is instrumented
with a 720 channel Delay Locked Loop based time-to-digital converter
(TDC) with a nominal bin size of 97ps. The TDC measures both the discriminator
leading and trailing edge times permitting a time-over-threshold approach
to the required discriminator time-walk correction. Hits from the
TDCs are sent to data buffering and concentrating
logic. The read-out uses four 3.2Gb/s serialisers with the high speed
clock being provided by a low-noise on-chip Phase Locked Loop. The
high data rates negate the possibility of buffering the data stream
whilst awaiting a trigger, thus a self triggering architecture with
continuous data readout has been adopted.
All configuration and state logic in the design deemed critical for
the correct operation of the chip has been triplicated to provide
increased single event effect tolerance. On-chip digital-to-analogue
converters provide threshold generation and trimming and are configurable
through a single-signal configuration interface. The configuration
and DAQ interfaces include a DC-balanced protocol layer permitting
direct optical connections when the detector assembly is installed
in the experiment. Dedicated calibration circuitry is included to
enable the required timing resolution to be reached.
The chip was manufactured in a commercial 130nm process during the
second half of 2013 and testing began at the start of 2014. Bump bonding
of the TDCPix chip to a P-in-N detector is currently being scheduled.
A detailed description of the ASIC architecture and performance will
be presented alongside results from the single chip assembly, if it
available in time.
Nov
26: Prof. Dieter H.H. Hoffmann, Technische Universität Darmstad
Title: TDCPix: Status and Perspectives of Search
for Dark Matter with the CERN Axion Solar Telescope (CAST)
Abstract: The CAST experiment is designed to search for solar axions
which are produced in the interior of the sun via the Primakoff effect.
The central part of the experiment, the helioscope is an LHC prototype
magnet that has attached different types of sensitive detectors for
x-rays in the regime of 1-10 keV. The experiment has been taking data
since 2003 and provided the most restrictive limits on the axion-photon
coupling in a broad mass range. Beyond 0,02eV/c**2 the mass the sensitivity
is degraded due to coherence loss. In order to restore coherence,
the magnet can be filled with a buffer gas providing an effective
mass to the photon. By changing the pressure of the buffer gas in
steps, one can scan an entire range of axion mass values. The CAST
experiment started this gas program entering its phase II at the end
of 2005. From 2005 to 2007, the magnet bore was filled with 4He gas
extending the sensitivity to masses up to 0.4 eV. From March 2008
onwards the magnet bore has been filled with 3He. With the end of
the 2011 data taking in July, the CAST experiment has covered axion
masses up to 1.18 eV surpassing the initial goal of the phase II which
was to reach 1.16 eV. The results of the first part of the 3He, with
a sensitivity up to 0.64 eV, have been finalized.
An overview on the current status of CAST and the future perspectives
will be given.
Dec
17 : Dr Hans Dijkstra, CERN
Title: Search for Heavy Neutral Leptons at the
SPS - Access to
the talk
Abstract: A new fixed-target experiment at the CERN SPS accelerator
is proposed that will use decays of charm mesons to search for Heavy
Neutral Leptons (HNLs), which are right-handedpartners of the Standard
Model neutrinos. The existence of such particles is strongly motivated
by theory, as they can simultaneously explain the baryon asymmetry
of the Universe, account for the pattern of neutrino masses and oscillations
and provide a Dark Matter candidate. The experiment will be motivated,
and previous searches will be reviewed. The experiment requires a
400 GeV proton beam from the SPS with a total of 2x10^20 protons on
target. The proposed detector will reconstruct exclusive HNL decays
and measure the HNL mass. The discovery of a HNL would have a great
impact on our understanding of nature and open a new area for future
research. In addition the experiment could accomodate a nu-tau detector,
which could increase the statistics of nu-tau interactions by more
than two orders of magnitude.
Colloque en vue de la nomination par appel d'un/e Professeur/e
Assistant/e
Jeudi 4 décembre à 16h00 - Grand Auditoire A - Ecole de physique
Dr Anna Sfyrla
Seeking supersymmetry with jets at ATLAS
Abstract :
With the discovery of the Higgs boson, all particles that the Standard
Model predicts have been experimentally confirmed. Despite its great
success, the Standard Model leaves unanswered several questions: why
is the Higgs boson a light particle, are the forces unified at very
high energies and what is the dark matter that astrophysical and cosmological
observations hypothesise. Several extensions to the Standard Model
are proposing solutions to these open questions, with supersymmetry
being one of the best motivated and studied. Supersymmetric particles
have been extensively searched for at collider experiments, evading
discovery so far. They decay dominantly to quarks, creating collimated
sprays of particles that are reconstructed in the detector as hadronic
jets. Final states with many jets have been thoroughly exploited in
the ATLAS experiment at the LHC. A roadmap of how this final state
provides a unique discovery potential in the searches for supersymmetry
is outlined and prospects for the higher energy and luminosity LHC
runs are given.
Semestre
de Printemps 2014
Feb 26: Prof Gennaro Miele, University of Naples - ANNULÉ
Title: Neutrino physics in the Planck era
Abstract: I briefly summarize the status of art about
the properties of relic neutrino distributions and the implications
of different neutrino scenarios on cosmological observables after
the first measurements by Planck. In particular I will pay particular
attention to the effects due to neutrino-antineutrino asymmetry and
to the presence of sterile degrees of freedom.
-------------------------
Mar
19: Prof Antonio Ereditato, Bern University
Title: Hunting for sterile neutrinos: short baseline
neutrinos at FERMILAB - Access
to the talk
Abstract : The "anomaly" constituted by the
LSND/MiniBooNE neutrino signal is still there after many years. This
points to the possible existence of sterile neutrinos.
An extensive short-mid term program aimed at solving the "puzzle"
is being conducted at Fermilab in the Booster neutrino beam, centered
on the use of new detectors based on the liquid Argon TPC technology.
A multi-step strategy envisions at first the use of the MicroBooNE
apparatus, being commissioned in the next months. In a second phase,
MicroBooNE will be possibly complemented by the LAr1-ND near detector,
being proposed to the Fermilab scientific committee.
This program and its prospects will be presented, as well as the parallel
work being conducted on LAr TPCs by the MicroBooNE/LAr1-ND Bern group.
-------------------------
Apr
09 : Prof Francesca Di Lodovico, University of London
Title: A window to the future: the Hyper-Kamiokande
project - Access to the talk
Abstract :In this talk we present the latest status
of the Hyper-Kamiokande project. The experiment, based in Japan, has
an extremely rich physics portfolio that spans from the study of the
CP violation in the leptonic sector and neutrino mixing parameters
to proton decay, atmospheric neutrinos and neutrinos of an astronomical
origin.
In particular, thanks to an upgraded beam power, we will focus on
the extremely high sensitivity to CP violation.
The project was recently selected as one of the top 27 projects by
the Japanese Science Council in the "Japanese Master Plan of
Large Research Projects" and is supported worldwide by the international
community. It is currently in the design and R&D phase.
In this talk we will review both the physics potential of the experiment
and the current design and R&D.
-------------------------
Apr
16: Dr Urs Baltensperger, Laboratory of Atmospheric Chemistry, Paul
Scherrer Institute
Title: Aerosol particle formation in the atmosphere:
the CLOUD experiment at CERN, the possible influence of galactic cosmic
rays, and comparison to field observations - Access
to the talk
Abstract : Atmospheric aerosol particles are liquid
or solid particles suspended in the atmosphere, with a size of approximately
0.001 - 100 μm. Atmospheric aerosols are of interest mainly because
of their effects on health and climate. Concerning health, many epidemiological
studies have shown a link between increased mortality/morbidity and
increased PM10 or PM2.5(particulate matter with
an aerodynamic diameter <10 and 2.5 μm, respectively). Concerning
climate, aerosol particles scatter and absorb light (known as the
direct effect on climate), and modify cloud properties (with a variety
of effects known as indirect effects). These effects are influenced
by the chemical and physical properties of the aerosol particles,
which makes these properties important to be measured.
Atmospheric aerosol particles are produced by a large variety of sources,
and are either emitted as primary particles (i.e., they are directly
emitted as particles into the atmosphere) or formed by secondary processes
(i.e., by transformation of emitted precursor gases). Depending on
the conditions, the latter may either result in homogeneous nucleation
of new particles or condensation of species on the pre-existing aerosol.
The mechanisms of new particle formation are still subject of debates,
but with the CLOUD chamber at CERN a facility is now available where
the relevant processes can be investigated without the artefacts of
previous studies [1]. Besides sulfuric acid, which for a long time
has been known as an important driver of nucleation, several other
components have been identified that increase nucleation rates by
many orders of magnitude compared to a pure sulfuric acid/water system,
including ammonia [1], amines [2], and organics [3]. The possible
influence of galactic cosmic rays is explored, and a comparison to
field observations is made.
References
[1] J. Kirkby et al., Role of sulphuric acid, ammonia and galactic
cosmic rays in atmospheric aerosol nucleation, Nature, 476, 429-433,
2011.
[2] J. Almedia et al., Molecular understanding of sulphuric acid-amine
particle nucleation in the atmosphere, Nature, 502, 359-363, 2013.
[3] F. Riccobono et al., Oxidation products of biogenic emissions
contribute to nucleation of atmospheric particles, (soon to be) accepted
in Science, 2014.
-------------------------
Apr 30: Prof Dainis Dravins, Lund Observatory
Title: Astronomical
Imaging a Thousand Times Sharper than Hubble: Optical Interferometry
with the Cherenkov Telescope Array - Access
to the talk
Abstract: Much of the progress in astronomy is led by improved imaging.
In the optical, one tantalizing threshold will be two-dimensional
imaging of stellar surfaces. With typical sizes of a few milliarcseconds,
bright stars require interferometry over kilometer-long baselines.
Although several concepts for such interferometer complexes on the
ground and in space have been proposed, their realization is not imminent.
However, the availability of large optical flux collectors (air Cherenkov
telescopes, in particular CTA – the Cherenkov Telescope Array – primarily
erected for gamma-ray studies) enable a revival of the quantum-optical
method of intensity interferometry, once developed for astronomy but
recently mainly pursued as boson- or HBT-interferometry in high-energy
particle physics.
The advantage of intensity interferometry is that it is insensitive
to either atmospheric turbulence or to telescope optical imperfections,
enabling very long baselines as well as observing at short optical
wavelengths. Telescopes are connected only electronically (rather
than optically), and the noise budget relates to electronic timescales
of perhaps 10 nanoseconds (light-travel distances of meters), enabling
the use of also optically imperfect telescopes.
CTA will cover an area of a few km^2, and with suitable software could
already quite soon become the first kilometer-scale optical imager,
reaching into novel microarcsecond parameter domains. It could reveal
the surfaces of rotationally flattened stars with their circumstellar
disks and winds, monitor a nova eruption, or possibly even visualize
an exoplanet during its transit across some nearby star.
-------------------------
May 07: Dr Elisa Prandini, ISDC, University of Geneva
Title: The gamma ray sky as seen with two MAGIC
eyes - Access to the talk
Abstract : In this talk I will review the most important
results achieved by the MAGIC Collaboration, which operates two 17-m
diameter imaging atmospheric Cherenkov telescopes in the Observatorio
del Roque de los Muchachos, in the Canary island of La Palma at 2200
m asl. The MAGIC telescopes cover the energy range from 50 GeV to
50 TeV with focus on the energy range below 1 TeV.
I will present recent scientific highlights including detailed multi-wavelength
studies of flaring blazars, detection of Crab pulsar bridge emission,
and morphology studies of galactic sources.
-------------------------
May
14: Dr Daniel G. Figueroa, Theoretical Physics Dept, University of
Geneva
Title: BICEP2: results and implications for cosmology
- Access to the talk
Abstract : I will describe the physics behind the recently
detected B-modes in the polarization of the Cosmic Microwave Background
(CMB) by BICEP2. I will describe the implications of this detection
for cosmology and for theoretical physics in general. Note: I'll keep
the discussion at a level accessible to non-cosmologists.
-------------------------
May
21: Dr Nicoleta Dinu, LAL, Orsay
Title: Silicon Photomultiplier – characteristics
and applications - Access to the talk
Abstract : The Silicon PhotoMultiplier (SiPM) is nowadays
the latest generation of solid state detectors in silicon technology
dedicated to visible light detection. In particular, it can be used
when multi-photon detection is involved and where low voltage operation,
low power consumption, insensibility to magnetic field, small spatial
resolution and compactness are required.
In this seminar, the device working principle as well as its electro-optical
characteristics will be reviewed. The application of SiPM arrays in
building very compact hand-held radiation detector used in therapeutic
purposes will be also presented.
-------------------------
May
28: Prof. Xin Wu, Department of particle physics, University of Geneva
Title: High Energy Astroparticle Physics in Space
with DAMPE and HERD
- Access to the talk
Abstract : High energy astroparticle physics in space is a very active
and diverse field of research that is playing a crucial role to connect
particle physics with astronomy and cosmology, and is complementary
to ground base astroparticle experiments such as large area air-shower
detectors, neutrino observatories and Cherenkov gamma-ray telescopes.
A large number of space missions have been successfully launched,
including AMS-02, PAMELA, FERMI, with several more in the construction
or planning phases, for example DAMPE, CALET, ISS-CREAM, JEM-EUSO,
HERD. In this seminar I will give an overview to the current status
of research in the field and discuss the science goals, detector concepts
and status of two missions that the Département de physique nucléaire
et corpusculaire of the University of Geneva is participating: the
DArk Matter Particle Explorer (DAMPE) satellite mission and the High
Energy Radiation Detection facility (HERD) facility on board the Chinese
Space Station.
Semestre d'automne 2013
Oct 2: Dr Marco Cirelli, Saclay
Title: Dark Matter Indirect Detection: status
circa 10/2013 -
Access to the talk
Abstract: Dark Matter constitutes more that 80% of the
total amount of matter in the Universe, yet almost nothing is known
about its nature. A powerful investigation technique is that of searching
for the products of annihilations of Dark Matter particles in the
galactic halo, on top of the ordinary cosmic rays. Recent data from
satellite and balloon experiments have reported unexpected excesses
in the measured fluxes of charged cosmic rays, which have been interpreted
as a possible first direct evidence for Dark Matter. If this is the
case, which DM models and candidates can explain these anomalies and
what do they imply for future searches? What are the constraints from
other measurements (such as those in gamma rays or neutrinos) and
from cosmology? And what is in store for the near future in this field
?
Oct 16: Dr Ugo Amaldi, Technische Universität München and TERA Foundation
Title: Particle Accelerators in Tumour Therapy
- Access to the talk
‘Hadrontherapy’, or ‘particle therapy’, is a collective
word which covers all cancer therapy modalities which irradiate patients
with beams of hadrons.
The most used hadrons are protons and carbon ions. Protontherapy is
developing very rapidly: more than 100'000 patients have been treated
and eight companies offer turn-key centres. Carbon ions, used for
about 8000 patients, have a larger radiobiological effectiveness and,
being a qualitatively different radiation, require still radiobiological
and, in particular, clinical studies to define the best tumour targets.
After a review of the rationale for hadrontherapy and of the accelerators
used in protontherapy, the European centres for carbon ion therapy
will be discussed. Finally the two challenges facing the physicists
and the engineers developing the accelerators for hadrontherapy will
be described: the construction of ‘single-room’ facilities for protons
and of multi-room facilities, not based on synchrotrons, for carbon
ions.
Oct 30: Dr Marco Durante, Darmstadt University
Title: Heavy Ions in Therapy and Space -
Access to the talk
Abstract: Research in the field of biological effects
of energetic charged particles is rapidly increasing. It is needed
for both radiotherapy and protection from the exposure to galactic
cosmic radiation in long-term manned space missions. Although the
exposure conditions are different in therapy and space (e.g. low-
vs. high-dose rate; total- vs. partial-body exposure), a substantial
overlap exists in several research topics, such as: individual radiosensitivity,
mixed radiation fields, normal tissue degenerative effects, biomarkers
of risk, radioprotectors, non-targeted effects. Late effects of heavy
ions are arguably the main health risk for human space exploration,
and with the increasing number of cancer patients (including young
adults and children) treated by protons and carbon ions, this issue
is now becoming extremely important in particle therapy as well. Reducing
uncertainty in both cancer and noncancer late risk estimates is therefore
the first priority in heavy-ion radiobiology: it is necessary for
a safe use of ion therapy in radiation oncology and for planning exploratory
missions, especially the Mars exploration. In addition, researchers
involved either in experimental studies on space radiation protection
or particle therapy often use the same high-energy accelerator facilities.
Several particle therapy facilities are now operating, under construction
or planned in Europe, USA, and Asia. It is foreseeable that the availability
of beamtime and the presence of many dedicated research programs will
lead to great improvements in our knowledge of biological effects
of heavy ions in the coming few years.
Nov 6:Dr Ivan Peric, Heidelberg University
Title: Particle Sensors in CMOS Technologies
- Access to the talk
Abstract: The use of pixel sensors implemented
in standard CMOS technologies has gained in popularity over the last
decade. The most prominent application is consumer electronics – the
sensors for digital cameras. CMOS sensors are also a promising option
for high energy physics. An overview of existing CMOS detector structures
for particle tracking will be given, and their properties compared.
Nov 13:Dr Carlos de Los Heros - Uppsala University
Title: Dark Matter searches in IceCube
-
Access to the talk
The IceCube Neutrino Observatory at the South Pole is the world's
largest neutrino telescope. It instruments a kilometer cube of ice
with more than 5000 optical sensors that detect the Cherenkov light
emitted by secondary particles produced in neutrino-nucleon interactions
in the ice. Covering a wide range of neutrino energies, from 10s of
GeVs to PeVs, its physics program is extremely rich. The talk will
focus on dark matter searches. In many models, dark matter gravitationally
concentrated at the center of the Sun or the galactic center can self-annihilate
to standard model particles, producing a flux of neutrinos from the
decays of the annihilation products. IceCube can look for such neutrino
flux, and competitive limits on the dark matter-nucleon cross section
and on the dark matter self-annihilation cross sections have been
obtained.
Nov 20: Dr Michelangelo Mangano, CERN -
Access to the talk
Title: Standard Model measurements at the LHC:
importance and prospects
Abstract: The key missions of the LHC include
the study of the Higgs boson and of electroweak symmetry, and the
search for new physics phenomena. These goals, nevertheless, rely
on the precise measurements of Standard Model (SM) particles, which
are the ultimate measurable decay products of any phenomenon emerging
from the LHC. The detailed and accurate study of the dynamics of SM
interactions, therefore, becomes a crucial step in fulfilling the
LHC's key missions. The dynamical regime exposed by the LHC, with
the highest energies ever produced in the laboratory, and the precision
required by the experimental measurements, challenge our ability to
deliver accurate enough theoretical predictions, and limit the fullest
exploitation of the LHC results. A global and coordinated campaign
of SM measurements and comparisons to theory will however greatly
enrich the outcome of LHC physics, increasing the sensitivity to anomalies
and new phenomena, and better guiding the interpretation of the data.
Dec 04: Dr Andres Sandoval, Physics Institute, UNAM, Mexico
Title: Recent Results from the HAWC - High Altitude
Water Cherenkov - Gamma Ray Observatory
Abstract: The High Altitude Water Cherenkov
(HAWC) observatory, under construction in Central Mexico at an altitude
of 4,100m, consist of 300 large light-tight water tanks instrumented
with 4 photomultiplier tubes each. Ground level particles from showers
produced by gamma rays and cosmic rays that collide with the upper
atmosphere are detected with these tanks. HAWC differentiates gamma-ray
and cosmic-ray primaries by their topology in the 100 GeV - 100 TeV
energy range with 2 sr instantaneous field of view and >95% duty
cycle. Since August of this year HAWC entered continuous operation
with 1/3 of the array. I will discuss construction and operation status
and the preliminary results. I will also summarize prospects for detections
of supernovae remnants, diffuse galactic sources, active galactic
nuclei, gamma-ray bursts, etc.
Semestre
de Printemps 2013
Feb 06: Prof. Laura Baudis, University of Zurich
Title: Dark matter searches with liquid xenon
-
Access to the talk
Abstract: We have strong evidence that about 80% of
matter in our Universe is dark, revealing its presence only by its
gravitational attraction. If the dark matter is made of Weakly Interacting
Massive Particles (WIMPs), it can be directly detected via elastic
scattering from nuclei in ultra-low background, deep underground detectors.
After a brief introduction to the direct detection method, I will
review current techniques based on liquid xenon as target material
to search for these hypothetical particles. The focus will be on recent
results, including those of XENON100, and on the most promising ideas
for the near future.
Feb 27: Dr Saverio Braccini, Albert Einstein Center for Fundamental
Physics, University of Bern
Title: The new Bern cyclotron laboratory for
PET radioisotope production and its beam line for multi-disciplinary
research - Access to the talk
Abstract: The new Bern cyclotron laboratory is based
on a 18 MeV proton cyclotron equipped with a specifically conceived
6 m long research beam line, terminated in a separate bunker. This
particular configuration is designed for industrial Positron Emission
Tomography (PET) radioisotope production as well as for novel detector,
radiation biophysics, radiation protection, materials science, radiochemistry
and radiopharmacy scientific activities. This project is the result
of the successful collaboration among the University Hospital in Bern
(Inselspital), the University of Bern, private investors and industrial
partners. This new facility is now operational and open to national
and international collaborations. The design, the construction, the
commissioning and the first research activities will be presented.
Mar 20: Dr Vittorio Boccone, University of Geneva
Title: A new technique in gamma astronomy: an
innovative camera for a high-energy gamma-ray telescope array - Access
to the talk
Abstract: Solid-state detectors, in particular Geiger-mode
Avalanche Photo-Diodes (G-APDs) represent a valuable alternative to
substitute the Photomultipliers in many applications.
The Cherenkov Telescope Array (CTA) is the first open-access high
energy (HE) gamma ray observatory and consists of many tens of telescopes
of three different sizes (Small, Medium and Large) covering a large
area on the ground.
We proposed a novel design for the Small Size Telescopes of CTA based
on a 4 m Davies Cotton reflector focusing the light on a large area
G-APD (developed by us together with Hamamatsu) array coupled to non-imaging
light concentrators.
I’ll first introduce briefly the physics motivations of CTA with particular
regards to the SST energy range and I’ll then give an overview of
the 4-m DC SST project. I will focus my talk on the R&D necessary
for the design and construction of the G-APD camera that was proposed
by the University of Geneva. I will describe the measurements necessary
to characterize the G-APD and I will discuss and compare our first
results to the design requirements.
April 24: Dr Roberto Cardarelli, University Tor Vergata
Title: Ultra low-noise amplifiers for silicon
and diamond detectors - Access
to the talk
Abstract: Thanks to the SiGe heterojunction, in the last years the
BJT transistor technology has been experiencing a great development
for high frequency and low-noise operation. The performance of an
ultra-low-noise preamplifier (500 e- RMS) with low frequency (100
MHz BW) will be shown. This amplifier, given the low dependence of
the noise from the source capacitance (up to 1 nF), the very fast
rise time (up to 100 ps) and the 50 Ohm input impedance, is particularly
promising for silicon, diamond and high rate gas detectors.
May 08: Dr Francesco Cafagna, Bari University and INFN
Title: The PAMELA mission: more than six years
of Cosmic Rays investigation - Access
to the talk
Abstract: The PAMELA mission major scientific objective is the measurements
of Cosmic Rays energy spectra, with special focus on the antiparticles,
i.e. antiprotons and positrons, ones.
The PAMELA apparatus is a satellite borne magnetic spectrometer and
comprises a time-of-flight system, a silicon-microstrip magnetic spectrometer,
a silicon-tungsten electromagnetic calorimeter, an anticoincidence
system, and shower tail catcher scintillator. It has been more than
six years that the PAMELA mission is taking data in space, on board
of the russian satellite Resurs-DK.
Important results have been obtained on the positron and antiproton
abundance and spectra. Moreover new results have been obtained on
the composition of the charged cosmic radiation that challenge our
current understanding of the mechanisms of production, acceleration
and propagation of cosmic rays in the Galaxy.
In this talk we will review the most recent scientific results obtained
by PAMELA and the apparatus performances during its six year mission.
May 15: Dr Jiri Krepel, PSI Paul Scherrer Institut
Title: Thorium or Uranium fuel cycle for advanced
nuclear reactors? Fuel recycling, multi-recycling, breeding and burning.
- Access to the talk
Abstract: Thorium fuel cycle provides several advantages,
which make it very attractive; e.g. lower waste production and possibly
improved reactor safety. However, there are also some drawbacks if
compared with Uranium cycle. The seminar will provide an overview
of basic physical features of both Thorium and Uranium fuel cycles
and comparison of their performance (criticality, breeding gain) and
safety-related (Doppler effect, coolant density effect) parameters,
with respect to the fuel recycling, multi-recycling, breeding and
burning.
May 29: Dr Mercedes Paniccia, University of Geneva
Title: AMS - First results -
Access to the talk
Precision measurement of the positron fraction in primary
cosmic rays from 0.5 to 350 GeV with AMS02
The Alpha Magnetic Spectrometer is a state-of-the-art particle physics
detector operating as an external module on the International Space
Station. It uses the unique environment of space to study the universe
and its origin by searching for antimatter, dark matter while performing
precision measurements of cosmic rays composition and flux. Since
its installation on May 19, 2011 it has collected over 30 billion
cosmic rays of energies ranging from several hundred MeV up to few
TeV.
In this talk we will present the precision measurement of the positron
fraction in cosmic rays in the energy range from 0.5 to 350 GeV based
on 6.8 million positron and electron events collected in the initial
18 month period of operation in space.
Semestre d'Automne 2012
Sept. 19: Dr Philipp Mertsch, University of Oxford and Kavli Fellow
at the Kavli Institute of Particle Astrophysics and Cosmology, SLAC,
Stanford University
Title: From radio halos to Fermi bubbles
Diffuse radiation fields pervade the Galaxy from radio waves to gamma-rays
and encode a plenitude of information about non-thermal processes.
For other studies, e.g. dark matter searches, CMB analysis or even
for faint point sources, they constitute an irreducible background
and need to be subtracted off. I will focus on diffuse Galactic emission
in the radio and in gamma-rays describing new ways to understand and
model them. Particular mention will be made of the recently detected
Fermi bubbles and I will suggest a theoretical picture that can explain
both their energy spectrum and morphology.
Sept.
26: Dr. Bill Murray (RAL):
Title: Higgs boson properties and how to constrain them
-Access to the talk
Abstract: The recently-discovered new boson at CERN seems to be a
good candidate for the long-sought Higgs boson. This seminar explores
what we need to learn about it to confirm that it is the Higgs boson
and how we will obtain that information. Some progress should come
rather rapidly at the LHC, but other information will be much harder.
If it is the Higgs boson then its existence at this mass presents
some interesting puzzles, and more detailed measurements may tell
us something about the dark matter binding galaxies together and maybe
the ultimate fate of the Universe.
Oct.
8: Prof. Subir Sarkar (Oxford)
Title: Alternatives to SUSY dark matter
- Access to the talk
Abstract: Much effort has been devoted to the study of weak scale
particles, e.g. supersymmeteric neutralinos, which have a relic abundance
from thermal equilibrium in the early universe of order what is inferred
for dark matter. This does not however provide any connection to the
comparable abundance of baryonic matter, which *must* have a non-thermal
origin. Candidate particles with such a connection are "dark
baryons" with mass of order 10 GeV from a new strongly
interacting sector. Putative signals in experiments such as CoGeNT,
CRESST and DAMA have also focussed attention on such particles. They
can affect heat transport in the Solar interior so as to affect low
energy neutrino fluxes and helio-seismology.
Oct.
31: Prof. Andrii Neronov (ISDC, University of Geneva)
Title: Gamma-ray astronomy in the 100 TeV band
Abstract: Small size telescopes (SST) sub-array of the next-generation
ground-based gamma-ray observatory CTA will extend the energy "window"
available for astronomical observations toward the 100 TeV energy
band. Based on the experience of observations with the current-generation
gamma-ray telescopes, HESS, MAGIC and VERITAS, we have some idea of
what kinds of astronomical sources and what kinds of astrophysical
phenomena we will observe in this new "extremely high energy"
(EHE) band. However, future observations of the sky in the up-to-now
unexplored EHE gamma-ray band might bring some surprising unexpected
discoveries. In this talk I will review the perspectives and challenges
of the new field of EHE gamma-ray astronomy which will be opened by
the SST sub-array of CTA.
Nov.
7: Dr. Mario Campanelli (UCL)
Title: Jet substructure as a tool to reconstruct the decay
of heavy boosted objects - Access
to the talk
Abstract: The LHC is the first collider where particles with mass
at the electroweak scale can be produced with momenta much higher
than their mass. The decay products of these particles are very boosted,
and Hadronic decays would be reconstructed as a single "fat"
jet. In the last few years there has been a great wealth of studies
in the field of hadronic jet substructure to reconstruct these final
states. In this seminar i will review the main phenomenological ideas,
as well as the first experimental results using jet substructure as
a tool to explore new and old physics.
Nov.
21: Prof. Alain Blondel, Université de Genève
Title: Future possibilities for precise studies of the
H(126) Higgs candidate - Access
to the talk
Abstrac: We present a summary of the state-of-the-art comparison relevant
to possible studies of the H(126) Higgs boson candidate. The machines
considered are the LHC and its upgrades, Linear and circular e+e-
colliders such as ILC/CLIC or LEP3/TLEP, gamma-gamma colliders and
muon colliders. The conclusions of the recent ICFA beam dynamics HF2012
workshop in Fermilab will also be shown.
Dec.
5: Prof. Max Klein, University of Liverpool
Title: Physics and Realisation of the LHeC
- Access to the talk
Abstract: The Large Hadron Electron Collider (LHeC) project involves
upgrading the LHC with a new electron beam in order to build a luminous,
TeV energy ep and eA collider at CERN. An introduction is given to
the physics programme of the LHeC, and the design concepts are described
of the 60 GeV electron accelerator and of a new detector for precision
deep inelastic scattering.
Dec.
12: Dr Daniel Muenstermann, CERN
Title: Radiation-hard Active Silicon Sensors for the ATLAS
Upgrade
Abstract: In the coming years, the LHC will be upgraded to provide
much higher luminosity. This implies increased radiation damage, occupany
and pile-up for ATLAS and requires the replacement of the current
Inner Detector with an improved all-silicon Tracker. While the standard
silicon sensor technology appears to be capable of fulfilling the
demanding HL-LHC requirements, new innovative technologies might offer
significant advantages.
Deep-submicron HV CMOS processes feature moderate bulk resistivity
and HV capability and are therefore good candidates for drift-based
radiation-hard monolithic active pixel sensors (MAPS). For the ATLAS
Upgrade, the concept of using a deep-submicron HV CMOS process to
produce a drop-in replacement for traditional radiation-hard silicon
sensors is explored. Unlike fully integrated MAPS, such active sensors
contain simple circuits, e.g. amplifiers and discriminators, but still
require a traditional (pixel or strip) readout chip. This approach
yields most of the advantages of MAPS (improved resolution, reduced
cost and material budget, etc.), without the complication of full
integration on a single chip.
After outlining the design of the HV2FEI4 test ASIC, characterization
results and first experience obtained with pixel and strip readout
will be shown before discussing future prospects of active sensors
and CMOS-based detectors in general.
Dec.
19: Prof. Julien Lesgourges, EPFL, Lausanne
Title: Active and sterile neutrinos in cosmology - Access
to the talk
Abstract: Review of status and prospects for constraining
the neutrino sector using cosmological observables, with an emphasis
on cosmic microwave background and large scale structure data.
Séminaires
exceptionnels - Candidats au poste de MER
Mercredi 18 juillet 2012 dès 08h30 - Auditoire Stückelberg
Ecole de physique, 24, quai Ernest-Ansermet, Genève
--------------------------------------------------
08h30-09h20 :Dr Chiara Casella (ETZH)
- From muon lifetime to positron emission tomography: Scintillators
and photodetectors in precision measurements
The detection of scintillation light produced by ionizing radiation
is certainly one of the oldest and still most widely adopted techniques
in particle physics. Based on my personal experience, I will describe
the experimental concepts and results of two different examples in
this direction: the FAST and the AX-PET experiments.
FAST is a high precision muon lifetime measurement, aiming at a 2
ppm accuracy on the muon lifetime tµ. This is achieved with
a DC p+ beam (170 MeV/c), stopped on a high granularity plastic scintillator
target, viewed by position sensitive photomultipliers (PSPM).
AXPET is a prototype for a novel geometrical concept of positron emission
tomography (PET), based on matrices of LYSO scintillating crystals
read-out by Silicon Photomultipliers (SiPM), for the detection of
511 keV photons. It aims at a high spatial resolution (~ 1 mm3) in
the reconstruction of the photons interaction point.
The working principle and the achieved results of the two experiments
will be described.
09h20-10h10 : Dr Domenico della Volpe (Università
di Napoli) - Unfolding the New Physics at LHC
The most recent results on the Higgs discovery with the ATLAS detector
will be presented. The mechanisms to generate the masses of the particle
in the frame of the Standard Model will be first introduced and then
the recents observation will be presented and discussed.
The success of the measurement has depended strongly on the trigger
system, which is fundamental to unfold the interesting physics process
from the huge background from underlying collision events.
As this is is my current area of research activity, I will present
the system's architecture and implementation and discuss the relevance
for the measurement.
10h10-10h40 : Coffee break
10h40-11h30 : Dr Pedro Facal (U. of Chicago)
- The microwave technique for the study of the highest energy
cosmic rays
The origin and composition of the ultra high energy cosmic rays (UHECRs,
those with energies above 1018 eV) have been studied for long. Recent
results by the Pierre Auger Observatory, a 3000 square kilometers hybrid
detector with unprecedented sensitivity, have shed a light in some of
the most pressing questions of the field, like the anisotropy in the
arrival directions and the mass composition. But these results show
also some of the limitations of the current techniques used for UHECR
detection. Recent laboratory measurements suggest that detection of
cosmic rays using microwave radiation in the GHz band is possible, and
would allow to cover large areas, as needed, with 100% duty cycle and
virtually no atmospheric attenuation. I will review the most recent
UHECR measurements and present the current efforts towards GHz detection,
in particular MIDAS, a prototype radio telescope instrumented with 53
microwave receivers at the University of Chicago.
11h30-12h20 : Dr Gerd Pühlhofer (Tübingen
University) - Hunting cosmic ray accelerators with TeV observations:
Clues from dark TeV sources and Supernova remnants
TeV observations of the Galactic plane hold the promise of identifying
the accelerators of Galactic cosmic rays. Indeed, current Cherenkov
telescopes have found a rich population of Galactic TeV gamma-ray
sources over the past few years. But identifying these gamma-ray sources
with astrophysical objects often turned out to be challenging. I will
report on lessons we learned throughout the identification process,
with a particular emphasis on supernova remnants which are believed
to be the main sources of Galactic cosmic ray particles.
12h20-13h10 : Dr Giulio Saracino (Naples University)
- An application of Silicon Photomultipliers to a tracking detector
for the muon radiography.
Silicon Photomultipliers have been developed about ten years ago and
their use, as an alternative to traditional photomultiplier tubes,
is increasing more and more. They have single photon response capability,
high detection efficiency, high gain at low bias voltage, low power
consumption and very good timing performance. In spite of their Geiger
regime, they can work as linear devices. All these properties motivated
their adoption for a tracker designed for the muon radiography of
volcanoes (muography).
Muography is a novel technique based on the measurement of the absorption
suffered by cosmic muons while traversing the volcano’s edifice.
It can provide a density map of the upper part of a volcano with resolution
better than 100 m. The detector is required to be able to work in
harsh environment and to have low power consumption, good angular
and time resolutions, large active area and modularity.
In this talk I will discuss the main properties of Silicon Photomultiplier
and the design, construction and first measurements of the muon detector
prototype developed for the MU-RAY project.
