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.
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 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.
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.
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.
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."
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!
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.
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 - Copyright © 2010-2015||Follow @iihe_bxl|