Professor Ulrik Egede

Overview

My research is in the area of High Energy Physics and deals with the most fundamental aspects of how our Universe works. We study the behaviour of the most fundamental building blocks of the Universe by accellerating particles to very high energies, colliding them and stidying the interactions taking place. These experiments are of a very large scale and only take place within international collaborations. I am involved in the LHCb experiment at CERN, the European Centre for Particle Physics (Geneva, Switzerland).

The purpose of both experiments is to gain an improved understanding of the flavour sector of particle physics. Quarks come in six different flavours and the two lightests ones (up and down) are the building blocks of protons and neutrons. The proporties of the charm and bottom quark are especially interesting. They form mesons (quark anti-quark pairs) with a relatively long lifetime and many different decay modes thus giving a rich field of study.

Our current knowledge of Particle Physics is described through what is called the Standard Model. We know this is only an effective theory as it predicts unphysical observables at energies close to the Planck Scale. Current studies are focused on looking for small deviations from Standard Model predictions that can give us an insight into the underying theory. We call these effects "New Physics" or "Physics beyond the Standard Model".

LHCb experiment

This is my current main research area. The LHCb detector is one of the four main detectors at the Large Hadron Collider.It started taking data in 2010. Its main focus is the study of the decays of b-hadrons which are bound states of quarks like the proton or the pion but with one of the light quarks replaced by a heavy b-quark. The decays we look for are very rare so we need to study lots of proton-proton collisions and then subsequently perform a huge data mining task. With 10¹⁵ proton-proton collision we have 10¹² b-hadrons created which is far beyond what we can store the data from. Real time data reduction (the trigger) takes this down to 10⁹ collisons which is still a huge sample to analyse. And that is just from a single years of data.

Rare decays

My main research topic is in what is called rare decays. These are decays where there is no direct transition of the quarks in the original b-hadron to the quarks in the decay products. This means that the decay is forced to happen through the creation of intermediate virtual particles. These virtual particles might be particles such as the top quakr and the W boson that we already know about, but it may also be particles that we have not yeat discovered (supersymmetric partners, graviton excitations, ...). What makes this research exciting is that we can gain information about these virtual particles by looking at the decay products. This is a bit like the childrens play where you put your hands into a box and have to work out the content without looking.

Results

The results we have at the end of 2012 have revealed a single result which at the moment is very hard to explain within the Standard Model. In the paper JHEP 07 (2012) 133 we determine the difference in the decay rate between the decay B⁺ → K⁺µ⁺µ^- and B⁰ → K⁰_Sµ⁺µ^-. They differ only by the substitution of a light u-qiark for a light d-quark. Within our current understanding of the Standard Model this should at most give a decay rate that differs by a few percent. But we observe a factor two difference, If this is a sign of some new and exciting area of physics or not, will require further analysis of this and other rare decays. It is for sure an exciting period though.