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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.

CMS

Shown here is a result of the 2012 LHC run at the Compact Muon Solenoid,

studying the invariant mass of electron pairs produced at the Large Hadron Collider. Shown is the data, as black dots, and the simulation predicting what we should expect according to the particle physics Standard Model (coloured bands). The IIHE is actively involved in the study of this kind of collisions, in collaboration with other groups of the CMS experiment. The data points agree very well with the predictions from the Standard Model, which means that up to now no new physics beyond the Standard Model could be observed that produces electron pairs. This could change when the LHC runs at a higher collision energy in 2015 and the high mass region to the right of the spectrum can be explored. New physics could show up as a peak in the high mass region of the spectrum, and could look like a small version of the peak of the Z boson that can be seen at a mass of about 90 GeV.

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.

CMS

Shown here is a record breaking event from the 2010 LHC run at the Compact Muon Solenoid,

a collision event with both an electron and very high missing transverse energy. The electron is represented by the red trapezoid (the length is proportional to the electron's energy), while the transverse energy is represented by the red arrow. Missing transverse energy is a quantity used to identify particles that did not leave a detectable signature. The IIHE is actively involved in the study of this kind of collisions, in collaboration with other groups of the CMS experiment. If the rate of these kind of collisions would be unexpectedly high, it would be a hint of the existence of, for example, extra dimensions.

IceCube

IIHE IceCube joining in celebration 100 years of Humans on the South Pole

IIHE IceCube joining in celebration 100 years of Humans on the South Pole 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. Hundred years ago, on the 14th of December 1911, the first human being arrived on the South Pole. Roald Amundsen led the original Norwegian team that arrived, so to celebrate this Norwegian triumph, the Prime Minister of Norway came to the South Pole for 4 days to engage in the festivities.

IceCube

Here you see an event recorded by IceCube in January 2008, when the detector was still in construction!

At that time, 22 strings were already taking data and 18 other strings were freshly deployed. Every colored bubble indicates the detection of one or more Cerenkov photons created by the cross of a charged particle by one of the sensors deployed in the ice. The size of the circles reflects the intensity of the signal. The color indicates the arrival time from red (early) to blue (late). These informations combined with the geometry of the detector allow first guess reconstructions of the initial track.

IceCube

IIHE students at the South Pole

Falling off the earth is a serious risk at the South Pole. Down there, at the very end of the world, everything is different.. 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.

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