TAEM- The Arts and Entertainment Magazine is constantly gathering the greatest scientific minds from around the world to interview so that all our student readers can learn from them. We are very happy to present Professor David Britton from the University of Glasgow, Scotland to readership. In case that you weren’t aware of the fact, our publisher’s father, and eight generations before him, were born in that fair city.
David, we are very proud to have you interview with us. Please tell our readers about your early education and how it prepared you for your future.
DB- My father was a physicist (PhD from Oxford and then worked with Marconi) who became a teacher after he was badly injured in a car crash and spent a long time rehabilitating. Neither of my siblings showed inclinations to follow in his footsteps but it must have been a good part of the reason why I took physics at university. During the last year of my undergrad degree, I was vaguely wondering what to do next when I saw a poster for the University of Victoria in British Columbia. It was a spectacular aerial view with the university in the foreground, surrounded by forest, and then the eye was led across the Strait of Juan de Fuca to the snowcapped Olympic Mountains in the background. On the spur-of-the-moment I applied and, to my astonishment, I was offered a funded place in graduate school there. I was hooked! At UVic I did an MSc in Nuclear Physics (a measurement of pionic atoms) and then a PhD in particle physics (looking at rare decays of the pion) at the TRIUMF facility located in Vancouver. However, there was one other key part of my early education that has had a big influence: I loved writing, though my spelling and handwriting were so awful that the teachers did not always reciprocate my enthusiasm! These days, I tell my students that their ideas are only as good as their ability to present them, and that writing and presentation skills are essential. I know it has been one of the things that has helped my career.
TAEM- You are a renowned Physicist in your own right. What made you choose this branch of science to work and teach in?
DB- I was inspired to take particle physics by a set of undergraduate lectures that described the investigation of cosmic-rays and the discovery of the muon and pion. I think I was attracted by the ultimate simplicity of reducing the complex world to its simplest building blocks. My PhD experiment was designed to address an exquisitely simple question: Are the couplings of the first and second generation of leptons the same? You see, there are, for reasons we don’t understand, three (and only three!) sets of building blocks in the universe. All the matter around us is made from the first generation (electrons, up and down quarks, and a few other things) but the other two generations are produced when enough energy is concentrated in, for example, collisions at a particle accelerator or in cosmic events. The second and third generation of particle differ in mass from the first generation but otherwise appear to be identical. So my PhD experiment was designed (not by me, I hasten to add!) to measure whether the pion coupled with the same strength to both the first and second-generation leptons. We managed to prove that it did and the result has stood the test of time. In an interesting footnote, over the last couple of years we have been re-doing the experiment with more modern equipment and hope to get an even more precise result in the next year or so.
TAEM- Please tell us about the subject that you teach, and the projects that your students work on.
DB- I have never taught very much because I always seem to have had some leadership role on a project that has taken most of my time. Currently, I lead the GridPP project, which takes about 75% of my time. I’ll tell you more about that later. After my PhD I moved to McGill University in Montreal and started to work more on building bits of the particle physics detectors. I worked on the ARGUS experiment at DESY in Hamburg (on a cool vertex chamber that had 100s of artificial rubies to position the wires) and then on the CLEO experiment at Cornell and the BaBar experiment at the Stanford Linear Accelerator (working on drift chambers for both of these). Naturally, I then ended up teaching detector physics at that time! When I moved to Imperial College in the mid-90s, I worked on the end-cap crystal calorimeter for the CMS experiment at CERN. The crystals were made of lead-tungstate and were incredibly heavy and yet completely transparent. I once took one through airport security in Geneva and the operators couldn’t understand how this perfectly clear crystal was so opaque on their x-ray machine! At Imperial, my team of students and research assistants set up a lab to measure some of the properties of these crystals to ensure that they would survive the radiation they would receive when the LHC was turned on and that we would be able to understand the signal they produced.
I moved to the University of Glasgow in 2007 and joined the ATLAS experiment and, later, the NA62 rare kaon decay experiment at CERN. As mentioned earlier, I also work on the re-run of my PhD experiment at TRIUMF (though I ran my shifts remotely over the internet!).
TAEM- Beside teaching at the University, you are also involved with the UK project, known as GridPP, where you are the project leader. Please describe this project for us and the importance of it.
DB- GridPP started in 2001 and over the last twelve years has designed, developed and deployed a computing Grid in the UK to enable the analysis of the data from the Large Hadron Collider (LHC) at CERN. GridPP is part of the world-wide LHC computing Grid that enabled the discovery of the Higgs boson, announced on July 4th 2012. I got involved in 2001 because the design of the LHC detectors was largely complete and there wasn’t so much of interest to do whilst waiting for the large construction projects to finish. Actually, to be strictly accurate, there wasn’t much money available to do interesting stuff since it was all committed to building the experiments. At that time, we had realized that we were going to be hit by a “data-deluge” when the LHC turned on and that traditional computing techniques (clusters, farms etc) were not going to cope. The Grid concept was just being conceived (Foster and Kesselman had just published a book by that title) and not only did it seem to offer a technical solution, it also seemed to match the global way high-energy physics was funded and organized. Simply put, the Grid joins up computers that are globally distributed such that the user does not know, or care, where the data is actually located or where the computation actually takes place. Yes, this sounds like the word “Cloud” that we hear all the time! Clouds hit the on-ramp to the hype-cycle in 2007 but evolved, in many ways, from the pioneering work on Grids earlier in the decade. In a similar way, the “Big-Data” buzz-word that has arisen more recently, also reflects the challenge we had to tackle…. a decade ago! To give you an idea of scale, the ATLAS experiment at the LHC has taken about 10 Petabytes (10,000 Terabytes or 10,000,000 Gigabytes) of data. However, this raw data has to be duplicated, processed, filtered, analyzed and simulated, so ATLAS actually has something like 140 Petabytes of data stored at the moment around the world. The CMS experiment will have a similar amount. Globally, the Grid connects up around 350,000 CPUs that do all the number crunching. In the UK we have about 40,000 of them and they are located at twenty different institutes across the country.
TAEM- You are also a member of the ATLAS collaboration, one of the projects underway at the Large Hadron Collider (LHC) at CERN. Please tell us about this scientific instrument and how this particular project is being conducted.
DB-The ATLAS experiment is the “Mr. Big” of particle physics detectors. Located in a cavern 100m underground, it is the height of a five-story building. It is 150 feet long and it contains over 100 million electronic channels. There is over 3000km of electronic cabling within the detector! It is basically a series of detectors that surround the interaction point where the protons within the LHC are collided. The innermost detectors track the particles in a magnetic field so we can figure out how many there are and their charge and momentum. After the trackers, there are various calorimeters that try to stop the particles and measure their energy. Finally, there is another set of tracking chambers that detect the muons that fly imperviously thought the calorimeters! ATLAS is an enormous collaboration and each of the 200 papers we have currently published has an author list of about 3000 scientists. Particle physics experiments have grown in size and complexity over the last 50 years and that has given the community the time to understand how to run such a complex and diffuse collaboration. Its not easy: Imagine running a company that spans over 50 countries and has thousands of employees but in which there is very little direct control or line-management. In particle physics, there is a “common goal” that helps hold it all together.
DB- If ATLAS is “Mr. Big” then CMS is “Mr. Heavy”. Although physically a little smaller, at 12500 Tons, it weighs a lot more than ATLAS! The primary reason that it is so heavy is because of the Lead Tungstate crystals that I talked about earlier. Both CMS and ATLAS are called “general purpose detectors” because they were designed to search for the Higgs particle and measure a wide range of other known, and possibly unknown, physics. There are two other detectors at the LHC with more specialized mandates. When the LHC turned on and started producing collisions, both the ATLAS and CMS detectors worked extraordinarily well. Both collaborations made use of the Grid to analyze their data, and both groups saw evidence of the Higgs boson at about the same mass. This was an amazing achievement. Looking for the Higgs is like looking for a piece of hay in a haystack, a much harder problem than finding a needle in a haystack because at least with a needle, one knows when one has found it. Individual Higgs events are indistinguishable from ordinary events and it is only by examining all the events and looking for tiny excesses at specific, but unknown, masses can the Higgs be seen. It is as if a hundred or so pieces of hay had been cut to the same length and then hidden randomly in a haystack. The only way to find them would be to sort every piece of hay in the stack by length and find the pile that statistically seemed to have a slight excess.
TAEM- We also learned that a recent possible discovery of the ‘God’ particle was made at the LHC. How important was this discovery to the realm of physics.
DB- Forbes magazine estimated that the cost of discovering the Higgs was $13.25 billion, so on a flippant note, it was pretty darn important for the future of physics that we found it! A more serious comment is that the LHC was designed to find the Higgs if it was there. In fact, at least for many theoretical physicists, it might have been more interesting for us to rule it out because we were in a position of knowing there must be something and if it wasn’t the Higgs, what on earth was it? We would definitely have seen something. I would hasten to add that Peter Higgs, after whom the particle is named, was rather relieved that it was found after all the effort! You might know that Prof. Higgs still lives nor far from here in Edinburgh where he did his pioneering work in the 60’s. Given that we have now found something, we are now at the start of many years of careful work, which will be required to understand exactly what it is and what its properties are. In a nutshell, the existence of the Higgs particle validates the Higgs mechanism as the means by which all matter gets its mass. Without this mechanism, we have no idea why matter has this property we call mass, at all!
TAEM- Your research was not just limited to the LHC. You also worked on very important projects in Stanford and Cornell. Please inform our readers about these and what they entailed.
DB- The universe appears to contain matter but very little anti-matter. This is a bit odd, because we also believe there was a big-bang and, naively, one would expect equal amounts of matter and anti-matter to be produced. So where did this asymmetry come from? The BaBar experiment at the Stanford Linear Accelerator made a precision measurement of something called CP-violation, which is one mechanism that leads to different behavior between matter and anti-matter. The effect is not big enough to explain the lack of anti-matter in the universe but it is one of the parts of the jigsaw. The CLEO experiment at Cornell was a precursor to the BaBar experiment and explored the properties of the B-mesons that were ultimately used in the BaBar experiment.
TAEM- Your expertise also was used in some very important research in Hamburg and Vancouver. What were these projects and how were you involved in them.
DB- I’ve already mentioned the PIENU (an acronym for PIon decaying to an Electron and NeUtrino) experiment in Vancouver, though not by name, which formed the basis of my PhD and which has been re-run over the last few years with an improved detector. I’ve had a very small involvement in the re-run but it’s the sort of thing I enjoy trying to contribute to on a Friday afternoon if all the crises of the week are (somewhat) under control! Fortunately, I have a research associate who can spend a little more time on it than me and it’s fun to discuss the latest plots he’s produced.
The ARGUS experiment in Hamburg was a competitor to the CLEO experiment at Cornell, at least it was until it was shut down in about 1991. It’s vitally important that scientific discoveries are independently confirmed, so there is a long tradition of building a minimum of two experiments to tackle the next frontier. Today, for example, we have ATLAS and CMS. In those days, both the ARGUS and CLEO experiments published hundreds of scientific papers but perhaps their greatest, and unexpected, discovery was the oscillation of neutral B-meson at a rate much higher than any one thought. This was an observation of a neutral B-meson spontaneously changing into its own anti-particle. Although this discovery was before my time, the ARGUS paper published in 1987 led directly to the idea of a “B-factory” and the construction of the BaBar detector at Stanford.
TAEM- David, it has been truly an honor to be able to interview you in our publication and I am sure that students world-wide will learn much from your research. Please promise to keep in contact with us with any of the projects that you may be involved with, now, and in the future.