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IIHE - Interuniversity Institute for High Energies (ULB-VUB)

The IIHE was created in 1972 at the initiative of the academic authorities of both the Université Libre de Bruxelles and Vrije Universiteit Brussel.
Its main topic of research is the physics of elementary particles.
The present research programme is based on the extensive use of the high energy particle accelerators and experimental facilities at CERN (Switzerland) and DESY (Germany) as well as on non-accelerator experiments at the South Pole.
The main goal of this experiments is the study of the strong, electromagnetic and weak interactions of the most elementary building blocks of matter. All these experiments are performed in the framework of large international collaborations and have led to important R&D activities and/or applications concerning particle detectors and computing and networking systems.
Research at the IIHE is mainly funded by Belgian national and regional agencies, in particular the Fonds National de la Recherche Scientifique (FNRS) en het Fonds voor Wetenschappelijk Onderzoek (FWO) and by both universities through their Research Councils.
The IIHE includes 19 members of the permanent scientific staff, 20 postdocs and guests, 31 doctoral students, 8 masters students, and 15 engineering, computing and administrative professionals.

Phenomenology

The pheno group — A hint for supersymmetry?

Particle physics phenomenology studies the implications of a theoretical model on experiments in high-energy particle physics and the other way round. From the experimental side, the CMS Collaboration observed in a certain search region 12 events more than expected based on the Standard Model of Particle Physics. Can this be explained by theories that go beyond the Standard Model like supersymmetry? Scientists from the pheno group at the IIHE as well as from the theory group at the ULB collaborated to answer this question. The figure shows how the number of events predicted by a simple supersymmetric model depends on the parameters of the model. The two free parameters, the mass of the stau and the selectron, are shown on the x- and y-axis while the number of events is indicated by the colours. Since we are looking for 12 events coming from new physics, we see from the figure that the model with selectron mass 145 GeV and stau mass 90 GeV can account for the observation of CMS.

IceCube

South Pole tuning in on "Skyradio"

The Askaryan Radio Array (ARA) is one of the future South Pole neutrino observatories focusing on the detection of neutrinos with energies beyond 10^17 eV. It utilizes radio waves, emitted from neutrino induced cascades in the South Pole ice sheet, to detect neutrino interactions. The detector is currently in the construction phase as is shown in the picture below. A grid of 37 antenna clusters, spaced by 2 km, is planned to be deployed in the South Pole ice at a depth of 200 m. By this, the full ARA detector will cover an instrumented area of about 100 km^2 and represent a state of the art detector for cosmic neutrinos in the energy range between 10^17 eV and 10^19 eV.

IceCube

The IceCube neutrino observatory at the South Pole is the world's largest neutrino telescope, completed in 2011 and taking data since 2005!

The detector is composed of 80 strings of 60 sensors deployed in the Antarctic glacier, between 1500 and 2500 m of depth. As its name suggests, IceCube covers an instrumented volume of one cubic kilometer. The DeepCore extension of IceCube is composed of 6 additional string in the center of the IceCube array, where the puriest ice can be found. At the surface, the IceTop air shower array equiped each IceCube string with 2 pairs of sensors in an ice tank of 3 square-meter.

CMS

The Compact Muon Solenoid forward tracker was partly built at the IIHE.

Here you see the assembly of several of the (black) support structures on which the tracker detectors were mounted. The IIHE contributed to the construction of the over 200 square meter silicon tracker, the most ambitious particle tracking detector ever built. Other contributions were made to the assembly of detector modules and the installation on the detector. Each detector element can identify the path of charged particles to a precision of up to 1/100 millimeters.

IceCube

Astroparticle Physics revolves around phenomena that involve (astro)physics under the most extreme conditions.

Cosmic explosions, involving black holes with masses a billion times greater than the mass of the Sun, accelerate particles to velocities close to the speed of light and display a variety of relativistic effects. The produced high-energy particles may be detected on Earth and as such can provide us insight in the physical processes underlying these cataclysmic events. Having no electrical charge and interacting only weakly with matter, neutrinos are special astronomical messengers. Only they can carry information from violent cosmological events at the edge of the observable universe directly towards the Earth. At the Inter-university Institute for High Energies (IIHE) in Brussels we are involved in a world wide effort to search for high-energy neutrinos originating from cosmic phenomena. For this we use the IceCube neutrino observatory at the South Pole, the world's largest neutrino telescope which is now completed and taking data.

CMS

Pinning down the bottom, charm and top quark

The bottom quark, discovered in 1977, is special, as in LHC collisions it usually lives in unstable particles that travel a few millimeters before they transition into particles that physicists can identify with our very accurate tracking detectors. At the IIHE we are leading the effort in the CMS experiment to identify bottom (or beauty) quarks. Bottom quarks are also extremely useful to identify top quarks, the heaviest known elementary particle, and Brout-Englert-Higgs bosons. At the IIHE we are also developing the tools to distinguish collisions containing bottom quarks from those where charm quarks are produced. This will be extremely useful to study how often top quarks decay to charm quarks instead of b-quarks, a very rare process in the Standard Model that if larger than expected would be a convincing sign for new physics!

IceCube

IceCube observes first hint of astrophysical high-energy neutrinos

Two neutrino candidate events detected at the IceCube Neutrino Observatory, dubbed "Bert and Ernie", are the two highest energy neutrinos ever observed so far, with an estimated deposited energy of about 1 PeV. The IceCube event displays of these two events are shown in the figures below, where for comparison one should realize that a single event covers an area comparable with the Maracana football stadium in Rio de Janeiro! The probability that these two events are not background, i.e. anything else in the detector besides astrophysical neutrinos, is at the 2.8 sigma level and does not allow claiming a first observation of astrophysical neutrinos. Further details may be found in Physical Review Letters 111 (2013) 081801. To improve the detection sensitivity, a follow-up search on the same data period has been conducted. The new analysis selects high-energy neutrino events with vertices well contained in the detector volume and exploits veto algorithms by using the outer layers of IceCube sensors. By means of this new analysis method 26 new events have been detected. The entire sample of 28 events has properties consistent in flavour, arrival direction and energy with generic expectations for neutrinos of extraterrestrial origin.

CMS

Looking in usually ignored collisions for physics beyond the Standard Model

It is commonly agreed that the standard model is not the ultimate theory and breaks down at higher energies. One of its most famous extensions is called supersymmetry or SUSY. Even though the CERN LHC data is already extensively examined for signatures predicted by this theory, no evidence has been found. However, supersymmetric models in which particles would have large lifetime (so would seem not to come from the collision point), have been mostly overlooked until now. IIHE physicists have performed a search that focuses on checking the LHC data for evidence of such a model. The picture depicts the transverse view of the CMS interaction point, showing a typical event from one of the possible signal with long life time. The definition of the leptons' impact parameter, d0, which is largely correlated with to the particle lifetime, is shown by the arrows.

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