Deep below the ground at the world's largest physics laboratory, Edinburgh scientists are shedding light on dark matter, black holes and the elusive Higgs boson. At the end of 2019, the University was invited to visit CERN and meet the researchers who share a vision of solving the universe's many mysteries.
A long, curved concrete tunnel lies 100 metres beneath the French-Swiss border. Reached by a fast-desending lift at the European Organization for Nuclear Research, better known as CERN, it's home to the world's most powerful particle accelerator – the Large Hadron Collider, or LHC.
LHC fires beams of protons in opposite directions around a 27-kilometre ring at close to the speed of light, creating collisions between the particles that recreate conditions that existed fractions of a second after the Big Bang. Detecting them allows scientists at CERN to study the first moments when all matter in the universe came into existence around 13.7 billion years ago. In doing so, they improve understanding of fundamental particles – the basic building blocks of nature – and the forces that control them.
What is CERN?
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Among a diverse international community of researchers poring over the vast amounts of data generated by the collisions are PhD students and staff from the University of Edinburgh. "CERN is an inspiring environment to work in," says PhD student Tom Carter. "You feel like you're part of a collective all working towards a common goal." This spirit of collaboration has led to numerous scientific breakthroughs since CERN began in 1954 with a mission to uncover what the universe is made of and how it works. Perhaps most famously, it is the site of one of the greatest achievements in particle physics: the discovery of the Higgs boson.
Finding the missing link
On 4 July 2012, following decades of work, scientists at CERN announced to the world that they had identified the particle – the missing link in the Standard Model of particle physics, a theory that defines our understanding of the physical world.
The famed particle is named after Peter Higgs, Professor Emeritus at the University of Edinburgh, who in 1964, along with five other scientists, predicted its existence and how it fit into the Standard Model. In 2013 – almost half a century after it was proposed – Higgs was jointly awarded the Nobel Prize in Physics with François Englert, another of the scientists who predicted the particle’s existence.
Studying the Higgs boson
Far from being the end of the story of the Higgs boson, this long-awaited discovery marked the start of fresh research at CERN to understand the particle's unique properties. The focus of research for Tom, who is spending the second year of his doctoral studies at CERN, is on precision measurement of the Higgs boson.
"After the discovery of the Higgs boson in 2012 it is important for us to understand its properties, and specifically how it interacts with other Standard Model particles," he explains. "There are many models that predict the existence of more than one type of Higgs boson. So, we're studying the particle discovered in 2012 to understand if it's the Standard Model Higgs boson, or a previously undiscovered one that could fit with another of these models."
Professor Victoria Martin, the University’s Chair of Collider Physics, contributed to the discovery of the Higgs boson in 2012 and continues to study the particle to this day.
"We know much more about the Higgs boson these days," she says. "We know how heavy it is – a bit heavier than a silver atom – and we know a lot about how it behaves. Right now, the Edinburgh team is trying to pin down some of the finer details of this behaviour, but this is still pretty tricky because the particle doesn't actually exist for very long."
The LHC is the only machine in the world that can produce Higgs bosons, but even with all its top-of-the-line technology, actually making one is still extremely rare. "They decay into other particles incredibly quickly," explains Professor Martin. "After 0.1 zeptoseconds, to be precise – less than one trillionth of a billionth of a second. This means we have to look through the data collected from trillions of proton collisions to find the few times a Higgs boson was created, and carefully analyse what happened."
Unearthing the mysteries of the universe
While physicists have learned a great deal since the 2012 discovery, there is still a lot about the universe that they don't understand. One of these mysteries is dark matter: "We know that dark matter isn't made of the same stuff as atoms, but we don't know what it is made of," says Proffessor Martin. "The Higgs boson could be fundamental to understanding that. For instance, it could be that it can interact with dark matter in a way that ordinary atoms can't. So, by looking at the Higgs bosons that we make in the LHC, we might be able to understand what dark matter actually consists of."
While there is understandably great interest in all aspects of the Higgs boson, Edinburgh physicists at CERN are also exploring many other avenues of research in attempts to answer some of humanity's other big questions.
One of them is Elena Villhauer, a second-year PhD student on the ATLAS experiment – one of CERN's four main projects – who is looking for black holes and dark matter. "One of the questions we're trying to answer is whether there are more than four spacetime dimensions, and we're doing that by looking for particular types of black hole," she explains. "If we find them, it would be evidence of extra dimensions, which would completely shatter our perception of our reality."
Elena is also working to improve the performance of the ATLAS experiment's detector – the enormous instrument that gathers data on the collisions created by the LHC. Like the collider, it's located 100 metres underground. At 46 metres in length and weighing 7,000 tonnes – almost as much as the Eiffel Tower – it’s one of the largest and most complex scientific instruments ever constructed.
"The LHC will be upgraded in a few years, so a lot of the detector’s sub-systems need to be improved too," she says. "I’m working on components called jet triggers, trying to maximise their performance so that we'll continue to get the most from the detector following the upgrade."
Pushing the frontiers of science
Among other experiments at CERN, Edinburgh physicists are also involved in projects looking at the differences between matter and anti-matter, and helping to develop prototype detector technology for the Deep Underground Neutrino Experiment – the biggest international science project in the US. Professor Martin believes the University will continue to be a strong partner in CERN.
"We're helping to develop new technology such as state-of-the-art detectors and data analysis techniques based on machine learning and artificial intelligence to look at the huge datasets generated by the LHC," explains Professor Martin. "CERN is also exploring plans for a new flagship project for beyond the LHC, and our group is already helping to plan this exciting future."
With students and staff working across such a diverse range of disciplines, Edinburgh physicists look set to continue helping to push the frontiers of science at CERN for years to come.
About the writer: Corin Campbell is a PR and Media Manager at the University of Edinburgh.