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.
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.
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.
Monojets as a possible signature for dark matter production at the Large Hadron Collider
Dark Matter is, almost a century after it was conceived, still only known to us through gravitational effects. Depending on its properties, there exists the exciting possibility of producing dark matter particles at colliders like the LHC. With the CMS detector, IIHE scientists search for direct production of dark matter particles in collisions like the one shown here: a jet (a spray of particles from a quark or gluon) recoiling against particles that escapes detection. This particular collision was the highest energy event of this type recorded by the CMS detector so far. Although it is most probably a background collision, dark matter could manifest itself in our detector exactly in such a "monojet" signature.
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 results challenge current understanding of Gamma Ray Bursts
Favoured candidates for the emission of Ultra High-Energy Cosmic Rays are Active Galactic Nuclei (AGN) and Gamma Ray Bursts (GRB), both spectacular emitters of high-energy gamma rays arising from particle acceleration in relativistic jets. However, the composition of the particles involved in these processes as well as the acceleration mechanism are very uncertain. The IceCube Neutrino Observatory at the South Pole is honing in on how the most energetic cosmic rays might be produced. IceCube is performing a search for cosmic high-energy neutrinos, which are believed to accompany cosmic ray production, and as such explores the possible sources for cosmic ray production. In a paper published in the 2012 April 19 issue of the journal Nature (Volume 484, Number 7394), the IceCube collaboration describes a search for neutrino emission related to 300 gamma ray bursts observed between May 2008 and April 2010 by the SWIFT and Fermi satellites. Surprisingly, no related neutrino events were found - a result that contradicts 15 years of predictions and challenges most of the leading models for the origin of the highest energy cosmic rays, as shown in the figure.
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.
Here you see the installation of the the Compact Muon Solenoid forward tracker,
which was partly built at the IIHE. The IIHE contributed to the construction of the over 200 square meter silicon tracker, the most ambitious particle tracking detector every built. Contributions were made to the assembly of detectors and their support structures, and the assembly of the detectors on a wheel such as you can see here. The tracker was installed inside the Compact Muon Solenoid detector in December 2007.
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!
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