Quarks and gluons

A powerhouse of theoretical physics, and one of the UK’s unsung heroes of science, Graham Ross laid out the pathway to the discovery of the gluon, the force carrier for the strong nuclear force that binds together quarks.

“Why the mathematics that we discovered should be relevant to the physical processes is surprising, I think, and something that may have a fundamental reason, but continually amazes me,” he says.

His work in developing the Standard Model of particles and forces has led to many new insights into the origins and nature of the universe. He even taught Richard Feynman how quantum chromodynamics, QCD, could be used to work out the interactions between quarks and leptons.

Professor Ross from the University of Oxford is the winner of the 2012 Dirac Medal awarded by the Institute of Physics.

Professor Graham Ross, Wadham College Library, 2012

Professor Graham Ross, Wadham College Library, 2012

Transcript

I’ve worked for many years trying to connect physical theories to experimental observation.

What inspired me about going into particle physics was, at the time, it struck me as being the most fundamental, where you had a chance of understanding more about the laws of nature.

The most exciting time has been when the gluon was discovered. When it was discovered at DESY it was certainly a very exciting and rewarding time for me to see the ideas I had worked on come to fruition.

What is amazing is that something as simple and elegant as the Standard Model can describe all of the forces in nature with the exception of the gravitational interaction

Professor Graham Ross in the gardens of Wadham College, Oxford, UK

Professor Graham Ross in the gardens of Wadham College, Oxford, UK

In the late 60s, our understanding of the nucleus was based on the idea there must be a strong force to overcome the electric magnetic repulsion of the protons, but the origin of the strong force was somewhat unclear.

I went to the laboratory at CERN in Geneva and there continued the work on field theory descriptions and strong interactions involving quarks. At that time it wasn’t commonly accepted that quarks existed. While I was there there was a fundamental discovery of the J/Psi, which is the bound state of the charm anti-charm quark, which initially people did not understand but subsequently realised that it could only correspond to quarks.

Gluons are central to our understanding of the strong interactions. They are the force carriers analogous to the photon which mediates the electro-magnetic reaction. They couple to quarks and bind them together.

What Jon Ellis and Mary K Gaillard and I did, was to realise that you could look for the gluon in an analogous way to the way quarks had been looked for by studying the jet of particles that they turn into.

So in a process in which you have an electron-positron annihilation into a photon, producing a quark, antiquark and gluon final state, you would expect to see three jets and their angular distribution would be characteristic of the interaction of the gluon with the quarks.

This was subsequently looked for at DESY and indeed they found unambiguous evidence that there was a new particle beyond the quarks which had the properties of the gluon.

That discovery was really fundamental to our understanding of the strong interactions.

I went from CERN to Caltech having some understanding of this development of the model of QCD for the strong interactions. Surprisingly this was not particularly well studied at the time.

At lunch I was sitting opposite Feynman, he was talking about his parton model, and I was surprised because at CERN we had learnt that we could calculate what went on inside the so-called ‘black box’ that Feynman had where the partons interact. And I said ‘why don’t you calculate this?’ So Feynman ignored me completely and carried on talking, and I thought ‘well, I am just a little person and it doesn’t matter.’ But he came into my office that afternoon and asked what I meant and I said: ‘well, we have a candidate theory called QCD which is quite promising.’ And for the next month or two he would come into my office occasionally. What he wanted to do was to discover QCD for himself and he would say what he’d done and I’d say that’s how it goes but you’ve missed something else.

So, my work which has largely been looking at supersymetric extensions of the standard model, ultimately relates to the nature of unification, be it grand unification or string unification. And one of the active areas that I am involved in is trying to make predictions for the standard model in the context of an underlying unifying string theory.

Why the mathematics that we have discovered should be relevant to the physical processes is surprising, I think, and something that may have a fundamental reason but continually amazes me.

Professor Graham Ross, Wadham College Library, 2012

Professor Graham Ross, Wadham College, Oxford, UK

About the film

Filmed on location at:

  • Wadham College, University of Oxford, Oxford, United Kingdom. September 2012.

Director: Martyn Bull
Producer: Thomas Delfs
Camera: Mark Whatmore
Editors: Liam Angell, Mike Willbourne
Cast: Professor Graham Ross

Production company: insitu
Client: Institute of Physics

Camera: RED Epic, Canon 550D

DESY images: DESY Deutches Elektron-Synchrotron
Standard Model Image: The Globe of Science and Innovation, CERN
Archive video: Courtesy of CERN
TASSO logbook: Sau Lan Wu/Symmetry
Caltech from the air: Tobin Frick/tobo on Flickr

Further reading

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