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HIGH-ENERGY PHYSICS (HEP): charting the invisible universe

From the universe down to the Brout-Englert-Higgs particle and superstrings: the researchers at the HEP@VUB research centre explore the very foundations of the infinitesimally large and the infinitesimally small. HEP@VUB unites the VUBs experimental and theoretical particle physicists. The frontier research performed by this unique platform in the field of particle astrophysics, the physics of particle collisions and theoretical high-energy physics attracts interest from around the world.

In the late 19th century, people believed physics no longer held any secrets. The few remaining elements that did not quite fit the picture seemed like mere details. But then a number of specific experiments corroborated the veracity of the theory of relativity and quantum physics. These observations caused major upheaval as they served to demonstrate that, at very high speeds and at atomic level, very different laws of nature apply than those that had hitherto been generally accepted. Courtesy of advances in technology, what had remained invisible to the eye up until then experiments were able to render visible under these extreme conditions. Nowadays too, science has empirical “standard models” from particle physics and cosmology that are in keeping with observations to a surprising degree. But it is very much the particular details of the measurements that may herald radical new theoretical insights. For instance, according to cosmological models that seek to describe the observations, just 5% of the energy density of our universe consists of the kind of matter we are familiar with. The remaining 95% consists of “dark matter” and the even more baffling “dark energy”. Again, it is up to us to try and observe and comprehend this ostensibly invisible realm. What is more, the most famous force of nature - gravity - is also the force which researchers least understand: the general theory of relativity puts forward an excellent description of gravity, yet this description does not apply to elementary particles at minuscule distances that are important to understand the Big Bang and what is inside black holes.

Sparked by the Big Bang, our universe is believed to be 14 billion years old. The Big Bang produced a hot primeval soup which has continued to expand and cool over time, to produce the unverse as we "see" it today. In a split second after the Big Bang, a number of phenomena occurred which were fundamental to the formation of the current universe. Which is why HEP@VUB researchers explore the physics at the highest energy scales that were important at the time, in order to gain insight into the substance and operation of the universe. They do so by causing elementary particles to collide at very high-energy levels inside particle accelerators and analysing the debris of these collisions, by using neutrinos as cosmic messengers of processes with even higher energies that unfold in the far-flung recesses of the universe, or by conducting theoretical research which seeks to record the fundamental laws of nature in a way that is mathematically consistent. These different methods are complementary and the HEP@VUB collaboration endeavours to arrive at innovative insights in this area.

Particle collision physics

Where do electrons and quarks, the building blocks of matter, get their mass from? For a very long time, the answer to this question had been an unknown. Until recently, when thanks to the Large Hadron Collider (LHC), the particle accelerator of the European Organisation for Nuclear Research (CERN), and the research efforts conducted over decades by the VUB team as one of many, the Brout-Englert-Higgs particle was discovered in July of 2012, as the crown witness of the mechanism which explains why our fundamental building blocks have mass. Particle accelerators such as the LHC are like very powerful microscopes in the way they work. With 27 km in circumference, the LHC is currently the most powerful particle accelerator on earth. New measurement data will hopefully tell us more about the nature of dark matter. 

Particle astrophysics


Courtesy of a worldwide collaboration project, in 2010 a telescope (IceCube) was built on the Antarctic, made up of 1 cubic kilometre of ice. IceCube detects neutrinos and in doing so gathers information on extremely high-energy physical processes in the corners of the universe. IceCube is synched up with satellite data 24/7. If a remarkable event occurs, VUB researchers get a signal from NASA, enabling them to check their database to see if the event coincided with high-energy neutrinos. As such, IceCube has already demonstrated that cosmic gamma ray bursts, which are believed to mark the birth of black holes, are insufficient to explain the energy of very high-energy particles that hit planet Earth (so-called cosmic radiation). Using the IceCube neutrino observatory, VUB researchers have come up with a method to trace the sources thereof, which have remained unexplained to date. 

Theoretical high-energy physics

How do we reconcile quantum physics and gravity? The answer to this question could well be string theory. By assuming that elementary particles are not point-like particles but tiny oscillating strings, the gravitational interaction is “spread” across the string as a whole, whereby the theory performs much better on infinitesimally small distance scales than does the general theory of relativity. One important unanswered question which the VUB team is looking into is whether string theory is capable of describing the Big Bang. VUB physicists are also resorting to techniques from string theory to simplify particularly complex computations of more conventional physical systems. 

In 2010, the VUB's HEP research was expanded with a team that is exploring the link between theory and experiment in high-energy physics, which remains unique in Flanders to this very day. 


Particle collision physics: Prof. Jorgen D'Hondt, Prof. Freya Blekman, Prof. Steven Lowette, Prof. Walter Van Doninck, Prof. Robert Roosen, Prof. Stefaan Tavernier 
http://w3.iihe.ac.be/en http://cms.web.cern.ch/ 

Particle astrophysics: Prof. Catherine De Clercq, Prof. Nick Van Eijndhoven
http://w3.iihe.ac.be/ and http://icecube.wisc.edu/

Theoretical high energy physics: Prof. Ben Craps, Prof. Alexander Sevrin 



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