Making history in particle physics
Interview: Dr Victoria Martin (University of Edinburgh)…
Making history in particle physics
Dr Victoria Martin is a Reader in Particle Physics in the School of Physics and Astronomy at the University of Edinburgh. She has spent most of her academic career in Edinburgh, graduating with a BSc in Mathematical Physics in 1996, followed by a PhD in Elementary Particle Physics four years later. From 2000–2005, she worked at Northwestern University and the Fermi National Accelerator Laboratory in the US, before returning to Edinburgh to become a Lecturer in Physics. She is currently part of a research team working on the Large Hadron Collider (LHC) at CERN, which discovered the elusive Higgs boson (the central problem in particle physics) in 2012...
Physicists and many other scientists can work for several decades on a project without ever seeing the fruits of their labours. Like many of her colleagues, Dr Victoria Martin has been grappling with the mysteries of particle physics for years, and was part of the team that discovered the Higgs boson at CERN (the European Organisation for Nuclear Research) in 2012; but, like Professor Peter Higgs himself, who waited 50 years for that magical moment when his theories were proved, her ultimate ambition is to make a contribution to the work of the next generation of physicists grappling with some of the same problems she has been facing for years. Hopefully along the way, says Martin, she will also confirm the recent findings about the Higgs boson and understand more about that other big question in particle physics – dark matter.
In modern science, individuals rarely make significant breakthroughs while working alone. Martin is part of a team of 3,000 researchers at CERN engaged in the ATLAS experiment, using the Large Hadron Collider (LHC) to investigate some of the most complex problems in physics, including the search for Higgs' elusive particle. And when papers are published describing their work, there are 3,000 names at the top, from about 100 different universities from all around the world. The team from Edinburgh currently comprises 20 researchers, with Emeritus Professor Higgs watching their progress with interest from his Edinburgh office.
Collaboration is essential to every experiment being conducted at CERN. There are four main experiments (including ATLAS) currently being conducted, involving a total of 10,000 researchers, and this creates a web of international connections. For example, Martin, who is currently the Co-chair of the Young Academy of Scotland, works in the same team as the Co-chair of the Young Academy of Flanders, Jorgen d'Hondt. Even though it deals with extremely big questions, physics can also be a very small world; d'Hondt is from the same research institute as François Englert, who was jointly awarded the Nobel Prize in Physics with Higgs in 2013.
Martin's work is focused on the ATLAS experiment, observing what happens at one of the four points where atoms collide at near the speed of light inside the LHC – a donut-shaped tunnel 17 miles in circumference. Every second, ATLAS (which can be described as “a huge digital camera”) captures 40 million three-dimensional images of these collisions and, using intelligent “filters” and a bank of computers to process the data, researchers keep 100 of the images for every single second – the most likely candidates for the Higgs' boson and other strange phenomena such as dark matter.
When lots of pixels light up in the image, there is a greater possibility the particle is there, but the original experiment was also a “shot in the dark.” According to Martin, researchers did not know four years ago if the Higgs boson existed, and if it did exist, they didn't know how it would behave.
The “boson boffins” were divided into two teams, looking for different “classes of behaviour.” Martin describes this as looking for something unusual – such as a “jaggedy shape” in an otherwise very smooth image. One image would not be enough, she explains. At least a hundred images were needed to confirm that the Higgs boson really was there, even though it only existed for 10-23 of a second.
Then one day, four years ago, the eureka moment finally arrived – followed by ten days of nail-biting tension to analyse the data and confirm the results. Martin herself was becoming increasingly nervous. Professor Higgs was also beginning to feel the excitement as rumours started reaching him in Edinburgh, but Martin and her colleagues still couldn't break silence, despite all the pressure for more information.
Then the magic number – five standard deviations – was confirmed. And the screaming began. They had finally cracked it.
The data confirmed the initial results, but the people at CERN needed five or six more days before they went public. Meanwhile, at a conference in Sicily, Higgs was told he “may be interested in coming along to CERN” later that week for a special announcement, but still the news wasn't official. In Geneva, one of Martin's colleagues queued overnight with a few hundred others for a seat in the seminar room, and Higgs himself was overwhelmed, describing the historical event as like watching his football team winning the Cup. “It was a very emotional moment for the whole team at CERN,” Martin says.
So after this incredible discovery, what next? And what is the purpose behind the research?
“Since we established its existence,” says Martin, “my own work has focused on trying to characterise the Higgs boson. As soon as we make one, it disappears immediately. So it’s a challenge to study its behaviour in detail.” Other researchers are still on the search for dark matter, to explain how stars and galaxies move through the Universe, but even though Martin is carefully following progress, she is heading in another direction.
The search began in 1964 when Higgs first developed his “very simple” theory – describing the Higgs field, the Higgs mechanism and the Higgs boson (which accompanies the Higgs field and provides us with physical evidence of its existence). To understand why this is so important, says Martin, consider the fact that the Sun is still shining as brightly as ever, despite the fact it’s full of hydrogen exploding all the time and forming helium, producing heat and light that make life possible on Earth. According to the basic laws of physics, the Sun should have burned up a long time ago, as one explosion leads to another in a huge chain reaction, but the Higgs field is delaying the “death” of the Sun by helping to slow down the interaction. If the Higgs field did not exist, says the theory, particles would not have enough mass to attract one another, and would float around freely at light speed.
“This is part of what we call the Standard Model,” says Martin. “It’s a very comfortable model, and explains almost all observations in particle physics to date, apart from dark matter. Understanding dark matter is one of the next big tasks for particle physics, along with, perhaps, super-symmetry and new effects of gravity, but that’s probably another 50 years of research down the line.”
Martin's current research focuses on looking deeper into the properties of the Higgs boson, investigating some of the outstanding questions about it, including “its couplings to the Standard Model fermions, the quarks and the leptons,” searching for evidence that the Higgs boson decays into “bottom quarks” (also known as beauty quarks). “An observation of the Higgs boson decaying into bottom quarks would provide strong evidence that the Higgs boson is well described in the Standard Model,” she explains.
“Although we have found the Higgs boson, the work of the LHC is not at all over,” says Martin. “After two years of upgrades, the LHC has restarted and is now colliding at even higher energy. And these more energetic collisions will be used to learn more about the Higgs boson, dark matter and perhaps other phenomena we’ve not even thought about yet.”
Asked why all this matters, Martin quotes the Nobel Prize-winning physicist Sir Joseph John Thompson, who is credited with the discovery of the electron: “The electron: may it never be of any use to anybody!” In other words, we don’t know yet what may result from the current research. There are numerous examples of technological by-products from work at CERN, including the World Wide Web, first developed by Sir Tim Berners-Lee to aid communication among scientists scattered all over the globe. The new generation of solar panels, says Martin, were also developed thanks to pioneering work on “super vacuums” for the LHC.
The next item on the agenda for Martin and colleagues is an even bigger atom smasher, which may not be constructed for decades. It isn’t easy making history in physics, but Martin believes it is worth it.