High energy physics

The Large Hadron Collider (LHC) is a huge scientific instrument situated 100 m beneath Geneva, used by physicists to study the fundamental building blocks of matter. Two beams of protons are accelerated in opposite directions in a ring 27 km in circumference until they are travelling faster than 99.99% the speed of light. These protons are then brought head-to-head within four detectors around the ring, corresponding to 600 million collisions every second.

For my DPhil thesis, I analyse data from the ATLAS experiment. ATLAS is a collaboration of over 3000 physicists from 38 different countries from around the world, all working together to probe our understanding of the Universe.

Event display of a H->4mu candidate event. ATLAS Experiment © 2012 CERN

Event display of a H->4mu candidate event. ATLAS Experiment © 2012 CERN

More specifically, my research involves searching for evidence of the Higgs boson, a fundamental particle predicted in 1964 by the Higgs mechanism of spontaneous symmetry breaking and mass generation. The Higgs mechanism played a crucial role in the development of The Standard Model (our best theory of the Universe) in the 1960s and 70s, and thus the search for this final unconfirmed particle became essential to confirming the validity of The Standard Model. After decades of searches, the Higgs boson was ultimately the main driving force behind the construction of the LHC. Although the discovery of a particle consistent with the Higgs boson was announced in July 2012, work is still ongoing to show with significant confidence that it is the Higgs boson predicted by theory.

I work as an analyser in the search for the Higgs boson decaying to two W bosons, which in turn can each decay to either an electron and a neutrino or a muon and a neutrino. It is these electrons and muons that we detect with the ATLAS detector. Selecting events where a Higgs boson has decayed and rejecting other ‘background’ processes that give the same final particles is a difficult task, both experimentally and theoretically. The Higgs to WW search is a particularly theoretically challenging analysis because it is not possible to reconstruct the mass of the Higgs boson from its decay products, and it is therefore very difficult to discriminate between signal and background. I personally focus on theoretical aspects of the search.