What is the Higgs boson?

Lyn - Well, the latter part of the 1960s was a mess. It was more like a whole zoo of particles being discovered all the time. We had, of course, the electron had been discovered by JJ Thomson and at the end of the 19th century, we had the proton and the neutron, and then we had many other kinds of composite particles that we really didn't understand. I came to CERN in 1969, and in January 1970, there was a lecture by Richard Feynman, Nobel Prize winner and a very gifted physicist. He gave a lecture on results that were coming out of Stanford Linear Accelerator Center at the time where they were probing the atomic nucleus of hydrogen and discovering structure inside that proton. There were more fundamental things inside there. And then things started to drop into place. What he was describing, it took a few more years to, to realise that he was describing the quarks. The most fundamental particles that make up the proton, first of all. And then the heavier atoms and the neutron are all made of much more simpler things. So from a zoo and a mess over my career, particle physics has distilled itself down to what is known as the standard model, and produces a very simple picture of something that looked extremely complicated in the 1960s.

Chris - Although people were quite quick to point out that it didn't explain everything. And that's presumably where Peter Higgs comes in and where the planning for the Large Hadron Collider comes in.

Lyn - That's right. So there were basically three families of quarks discovered, and the big problem there was they all had different masses. And then the question is, what was behind all of this? What generated mass? How did they obtain the mass? And it was actually in 1964 that Peter Higgs wrote a paper on what is now called spontaneous symmetry breaking in the electroweak sector. That sounds very complicated, but I was with Peter Higgs about a year ago. We went to have a beer in the pub, and there was nowhere to sit except there was half a table spare. And so we joined a coal miner from Fife and his wife. Peter's, not Scottish, this was in Edinburgh, but he'd been in Edinburgh for many, many years. Peter started to, to tell them a lot of the history of this region of Edinburgh that we were in. And the guy said, you are a very clever man. And I said, he should be. He does have a Nobel prize after all. And then Peter gave them a half hour lecture on spontaneous symmetry breaking in the weak interactions to which they listened intently, but <laugh>, they'll go away with that memory, of course. But it was extremely funny.

Chris - You are there in that part of the 1960s. We know that we've begun to see some order being brought to this what we now call the Standard Model. We know, identified by scientists like Peter Higgs, that there's some gaps there, including explaining why things have the masses that they do. So why did it become apparent that we needed a really powerful particle accelerator to get underneath this problem? Why was that the next step? Was it just a question of, well, we've, we've smashed things together with a certain energy, if we do it harder, we might find even more. Was that the mentality, the thinking?

Lyn - The mentality is if you want to create massive objects, then e equals mc squared. The most famous equation in physics. If you want to create the heavier elements of the standard model, the heavier quarks, you need more energy. But things went in an interesting way. It wasn't straight to the Large Hadron Collider by any means. In 1970 to 1973, there was an experiment at CERN using the tool of the day, which was a bubble chamber. A bubble chamber contains a liquid, super saturated liquid, which when a particle goes through it, it leaves a track. And there was this bubble chamber called Gargamelle, where they made a very important discovery of what were called weak neutral currents. Because there are not only the matter particles, there are not only the quarks and leptons, there are also the force particles. The force particles are basically the photon for electromagnetism, the gluon which is holding the atomic new nucleus together, the strong interaction. Things called the W and Z boson, which are responsible for the weak, very weak interaction. It's weak, but it's very important because that's the way the sun works. That's the way we get life. And these W and Z bosons, because of the experiments on the Gargamelle bubble chamber, were predicted to exist and their mass was predicted. So we actually modified the super proton synchrotron, which I had been working on building, into a colliding beam to smash the nuclei of hydrogen, the protons together to try to create these W and Z bosons. Except that we had to be much more sophisticated and we had to collide protons with antiprotons. Every metaparticle has got its antimatter equivalent, which does not exist in normal life, but we can create it in our accelerators. So we built a machine and we discovered the W and Z bosons. And there was only one thing left to discover, to complete the standard model, and that was the Higgs boson. So that was the Standard Model complete apart from the thing that holds it all together - the particle that creates mass, and that was predicted by Peter Higgs himself a long time ago actually, but couldn't never be found because nobody knew what its mass was. And if you don't know what his mass is, you don't know if you've got enough energy to create it.