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Oliver, 1st Year

Professor Mark Thomson

Since high school I have been fascinated by Particle Physics. The fact that humankind has been able to develop a profound understanding of nature at this most fundamental level is a remarkable achievement.

Because of my interest in particle physics, I choose to study physics rather than mathematics at Oxford. I stayed at Oxford for my doctorate, where I worked at the interface between particle physics and astrophysics, trying to see the stars by studying the high-energy cosmic-ray particles that made it half a mile underground to the Soudan-2 detector located in an Iron mine in Northern Minnesota.

After receiving my doctorate I moved into more mainstream particle physics when I joined the OPAL experiment at CERN. This was one of the four large particle detectors detecting the collisions of electrons and positrons (the anti-matter equivalent of electrons) at the 27 km circumference Large Electron Positron (LEP) collider, located in the circular tunnel that now hosts the LHC. Here I briefly worked as a post-doctoral researcher at UCL and then moved to Geneva semi-permanently when I got a research scientist position at CERN. Here I spent six enjoyable years dividing my time (although not equally) between research, skiing and learning about wine. I was fortunate enough to play leading roles in a number of the central measurements made at LEP, focussing on the precise studies of the properties of the W and Z bosons, the particles responsible for the weak force. Although the W and Z bosons only live for about 0.0000000000000000000001 of a second, we were able to make measurements of sufficient precision to have sensitivity to quantum corrections from the then undiscovered top quark and Higgs boson.

When the LEP project ended in the year 2000, to make way for the preparations for the construction of the Large Hadron Collider, I had to decide where my future would lie. Fortunately at this time a lectureship position in Particle Physics was advertised at Cambridge; I duly applied and was interviewed. A few weeks later, whilst skiing in glorious sunshine in the high-Alps at Argentiere, I received a phone call telling me that I had been offered the job. Swapping the Alps for the fens was not the easiest of decisions… The transition was made easier by being offered a Fellowship at Emmanuel College; amongst Cambridge undergraduate students Emmanuel has the reputation for being the friendliest college, fortunately this also extends to the academic staff.

With the end of LEP and moving to Cambridge, I had the opportunity to pursue my research interests in a different area of particle physics; neutrino physics. Neutrinos are elusive particles that only interact weakly with matter – a million billion (1015) of them pass serenely through each one of us every second. On arriving to Cambridge, I joined the MINOS experiment, which involved firing an intense beam of neutrinos a distance 735 km from Fermilab, just outside Chicago, to a 5400 tonne detector in the Soudan mine in Northern Minnesota (back where my research career started). Although most of the neutrinos would pass through the Earth’s crust and the MINOS detector (flying off into deep space at the speed of light), a minute fraction would be detected. By studying the way the neutrinos changed their type “flavour” on their 735 km journey it was possible to make precise measurements of the properties. By the time the MINOS experiment ended in 2012 (although it lives on as MINOS+) the Cambridge research group had made major contributions to the measurements of muon neutrino disappearance, the search for electron neutrino appearance and the study of atmospheric neutrinos.

Most researchers working in particle physics focus on one particular area. I have been fortunate in being able to maintain a number of interests. In parallel with working on the MINOS experiment, I worked on the ATLAS experiment at the LHC and have played a major role in developing the physics case and detector design for what will hopefully be the next particle physics collider experiment – the International Linear Collider (ILC). If all goes well, the ILC could be operational in Japan before the end of the next decade. The ILC will be a 30 km long high-energy electron-positron linear collider, with the main goal of studying the recently discovered Higgs boson with much greater precision than possible at the LHC.  The Higgs boson really is a completely new form of matter, unlike anything else we have seen and the detailed study of its properties may well provide a window into physics beyond our current understanding.

Being a Cambridge academic is not all about research; a passion for teaching is absolutely essential to the development of the next generation of scientists. Within the physics department at Cambridge, I taught the final-year particle physics course for five years and in 2013 published a major undergraduate textbook based on this course, entitled “Modern Particle Physics”, which spans both theory and experiment and covers all the main areas in contemporary particle physics, including the discovery of the Higgs boson.

Teaching is also an essential aspect of being of being a fellow of Emmanuel College. This is something I have always taken very seriously and, fortunately, it has always been a pleasure teaching our excellent undergraduate physics students, a significant number of whom have now embarked on careers in particle physics in the UK, at CERN and beyond.

It has been a long journey from my schoolday interest in particle physics to where I stand now, but what next? I will continue to combine my interests in collider physics (ATLAS, ILC, CLIC) and neutrino physics, where Cambridge is playing an important role in the work towards the realisation of the next generation of accelerator-based neutrino experiments (LBNE and MicroBooNE) using the technologically exciting liquid Argon detectors. And to keep me busy, perhaps another book is on the horizon…


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