Experimental Particle Physics Research Group

Matter / Antimatter Asymmetry

Our best theories of the Universe strongly indicate that matter and antimatter were created in equal and opposite amounts in the Big Bang, and in a massive mutual annihilation they wiped each other out – almost but not quite completely; there was a tiny (part per billion) bit of matter left over at the end, which now constitutes all of the matter in the Universe. The question of why there was anything left over at all – which is fundamental to our existence - has been an outstanding mystery of cosmology for decades.

Philip leads the Sussex neutron Electric Dipole Moment (nEDM) group, which is dedicated to uncovering the matter anti-matter asymmetry as a small distortion in the shape of the neutron, a subatomic particle. The nEDM group is been responsible for the best limit in the world over the last two decades. Although it’s electrically neutral, one end will be a little bit positive and the other end a little bit negative. Different cosmological theories predict different amounts of distortion, so measuring it puts tighter and tighter constraints on new theories of physics beyond our current understanding. Indeed, it’s been said in the literature that, if taken as a whole, the neutron EDM experiment has probably ruled out more theories (of new physics) than any other experiment in history.
B mesons are exceptional particles as they show incontestable evidence of nature distinguishing between matter and antimatter: a universal phenomenon not yet fully understood. These particles offer a very prolific testing ground to finely test our understanding of the Standard Model of particle physics and our models of particle-antiparticle asymmetry. Alex C is working with Fabio and Ioannis on the ATLAS measurement of beauty hadron decays with leptons, where any anomalies observed may be due to new physics contributions. They recently set the most stringent limit available on the decay of the Bd meson into two muons and are working on improving this analysis as well as looking into possible new ways of probing lepton-related anomalies in flavour physics processes.