Discovery of Matter Anti-matter Asymmerty in the Charm Sector

Symmetries play an essential role in our understanding of the universe. Nature exhibits a stunning level of symmetry across all scales, from the bilateral symmetry of many animal's bodies to the mathematical symmetry of the fundamental physical laws. But only the imperfections of symmetries reveal the full picture. In astrophysics for example, the anisotropy of the cosmic microwave background radiation has given insight into the structure of the universe roughly 300,000 years after the big bang.

At the Large Hadron Collider (LHC) we study the type of physics which governed the processes just a fraction of a second after the big bang. The LHC, located 100m underground just outside Geneva, collides protons at energies that have never previously been reached in a laboratory on earth. The smallest of the four large experiments at the LHC is known as LHCb, and is specifically designed to discover asymmetries in the behaviour of matter and antimatter.

In our current understanding, matter consists of twelve fundamental particles: the six quarks (u, d, s, c, b, t ordered by increasing mass), and an electron with its heavier partners muon and tau and their three associated neutrinos. These interact by the exchange of so-called bosons, which are fundamental force carrying particles. The standard model of particle physics (SM) explains these matter interactions and has so far held up to all experimental tests. However, it fails to give explanations to basic questions like the reason why the t-quark is over 50,000 times heavier than the u-quark. Another is the puzzle that perfect symmetry would lead to equal amounts of matter and antimatter and the annihilation of the universe shortly after the big-bang. Questions like these tell us that the SM does not cover all aspects of fundamental interactions and therefore has to be extended.

Nature has given us three special laboratories to study matter and antimatter interaction: neutral mesons (called K, B and D-meson), particles consisting of one quark (matter) and one antiquark (antimatter). These mesons periodically change into their antiparticle and back, a process called mixing. The studies of two of these systems (K and B mesons) have led to Nobel-prize winning breakthroughs. I will study the mixing phenomenon in the third system, known as the D-meson system. Particularly, I will be looking for a tiny asymmetry in this process, an asymmetry between the behaviour of matter and antimatter. Such an asymmetry has been observed in the K and B-meson systems but remains to be detected in D-mesons.

The LHCb experiment is the best apparatus for measuring D-mesons for at least the next decade. The asymmetry in D-mesons I am looking for is predicted to be tiny in the SM. The precision we can achieve allows the observation of this effect if it is enhanced beyond the SM level. Detailed analyses of several processes involving D-mesons cannot only give evidence for new physics phenomena but also allow to identify the type of new physics by comparison with existing models.

Particle physics research continues to lead to technological benefits to society, from the World Wide Web to medical imaging, but its true purpose will always be the search for fundamental understanding of our universe. My goal is to further this understanding, using the matter-antimatter asymmetry to reveal nature's beauty. And true beauty lies in imperfections.