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|News||Congrats to IIHE CMS student Cécile Caillol, who was elected as CMS fundamental physics scholar!|
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.
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.
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.
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!
Dark matter searches with IceCube
According to the most recent observations and based on the standard model of cosmology, dark matter makes up 26.8% of the energy density in our Universe The argument that yet to be detected Weakly Interacting Massive Particles (WIMPs) make up the dark matter is compelling. Over time, WIMPs may accumulate in the center of the Sun and Earth, and annihilate with each other. The decay products may vary, and most of them will interact and decay in the massive body. If neutrinos are created from those secondaries, they will escape and provide a neutrino ﬂux. This neutrino flux could be measured by the IceCube Neutrino Detector. Data taken by AMANDA and IceCube have been analysed at the IIHE to search for WIMPs in the centre of the Sun and Earth; no significant excess above background was observed so far.
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.
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.
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.
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.
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