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.
The needle in the haystack
Physicists working in the CMS experiment regularly have to spend their time searching for a needle in a haystack. In other words we look for the rarest of rare collisions that represent very unlikely physics processes. An example of work done at the IIHE is the search for the production of four top quarks (the needle) in the huge dataset recorded by CMS in 2012 (the haystack). Our results put an extremely tight limit on the production of four top quarks, indeed the tightest limit at the LHC so far. As four top quarks are also produced in many new theories of physics such as supersymmetry, this limit can tell us a lot about the validity of these theories.
IIHE at the ICRC!
The 34th International Cosmic-Ray Conference took place in The Hague, The Netherlands from July 30 to August 6, 2015. More than 800 physicists attended the conference to discuss the latest progress in cosmic-ray and solar physics. Furthermore, recent developments in gamma-ray and neutrino astronomy as well as the hunt for dark matter were covered. The IIHE was clearly represented with 8 posters and 3 talks. Our members presented their results on the Earth WIMP (Weakly Interactive Massive Particles) searches, a possible dark matter candidate, and on multiple analyses that aim to find the sources of neutrinos emission with the IceCube Neutrino Observatory. We focus our attention on: sources with spatial extension in the sky (from 1° to 5°), Gamma-Ray Bursts - extremely energetic explosion possibly associated with the death of a star, Dust Obscured Blazars - a special type of galaxies - and solar flares. The Askaryan Radio Array (ARA) as well as a totally new way to observe high energy neutrinos using radar detection were the subject of two talks! Also, two of our new members presented their previous work on the Cherenkov Telescope Array (CTA) and the Very Energetic Radiation Imaging Telescope Array System (VERITAS). The 35th ICRC will take place in Busan, South Korea, where we hope the IIHE will be even better represented!
Candidate top quark +W boson collision event at CERN
Shown is a candidate collision event from the 2010 LHC run that was selected in the search for one top quark associated with a W boson at the Compact Muon Solenoid experiment at CERN. IIHE scientists are leading the analysis effort in the detailed study of these kind of collisions. Understanding single top production is relevant both for the detailed understanding of the physics of top quark production but also in the context of the Standard Model Quantum Chromodynamics in general as this process is special because of the production of a single heavy quark in association with a gauge boson. This event topology is very similar to that expected for new physics or the elusive Higgs boson, for which this kind of events are a background.
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.
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.
First results from a realistic modeling of radio emission by particle cascades in ice
In the previous decade several new experiments (ANITA, NuMoon, ARA, ARIANNA) were proposed to detect high energy (>EeV) neutrino induced particle cascades in dense media such as ice, salt, and moon rock. At the highest energies, these neutrino's are extremely rare and a large detector volume is needed to detect them. Due to the long attenuation length, the detection of the produced radio signals is the most promising tool to search for these rare events. In light of these new experimental efforts, the EVA-code, originally constructed to model radio emission from cosmic-ray-induced air showers, is under development to model radio emission from particle cascades in the South-Pole ice. The ice geometry is included into the code, as well as a parameterized model for the particle cascade. Furthermore, the original EVA-code already incorporated Cherenkov effects in the emission for radio signals moving on curved paths due to a density gradient in the medium. The figure below shows a preliminary result for the electric field as seen by an observer positioned at the ice-air interface. The particle cascade starts at 330 meters depth traveling approximately 10 meters straight upward in the ice until it dies out. The pulses as seen by observers at different lateral distances ranging from 10 m to 300 m are shown. It is seen that the pulse becomes sharper moving outward toward the Cherenkov cone at a lateral distance of approximately 330 meters."
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.
IIHE students at 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.Here you see a really cool phenomenon made by ice crystals that are drifting in the air at low levels and acting as prisms for the light rays passing through them. In this way, a halo around the sun is visible. In this picture, IIHE PhD Student David put his head in front of the sun and the halo becomes visible more easily.
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