The big question

Cambridge team joins ALPHA hunt for dark matter

It’s considered a ‘table-top experiment’, using apparatus that fits into a university lab, but the scale of its ambition couldn’t be much bigger – to expand our understanding of the Universe’s fundamental structure.

A team of Cambridge scientists are working with colleagues from around the world on the new Axion Longitudinal Plasma Haloscope (ALPHA) project to identify the composition of dark matter, the mysterious and invisible material believed to make up 85 per cent of all the matter in the Universe.

The newly funded international experiment will use a powerful superconducting magnet to search for axion particles, one of the most-favoured candidates for dark matter. Axions were named after a washing powder, because the idea washes clean some fine-tuning problems in the Standard Model of particle physics.

“We have the potential to make a groundbreaking discovery,” says Hiranya Peiris, Professor of Astrophysics (1909) at the Institute of Astronomy, and a founding member of the ALPHA collaboration. “The fact that we only understand 5% of the matter that makes up the Universe, all the stars and the galaxies, means there’s a huge hole in our fundamental understanding.

“So much of the dark Universe is still a huge mystery, but dark matter is something we can actively experimentally look for in the laboratory, and that’s what makes this project so exciting.”

To do this, a metamaterial-inspired resonator-based experiment will be built, and sited at Yale, in an existing 16 Tesla magnet. Compared to the enormous underground cavern sites needed to test for weakly interacting massive particles (WIMPs), another compelling candidate for dark matter, the ALPHA equipment needed to test for axions will be tiny. A ‘tuneable’ array of wires aims to allow the resonator to detect the axion – which is coupled to a photon – as an energy field, rather than a particle.

“Even when you amplify the tiny electric current that signals axions, it’s still really small,” says Professor Peiris. “So you need very sensitive equipment to measure it. And that’s why being awarded this funding – to build the full-scale experiment, not just a prototype – is such an amazing opportunity. What we’re trying to understand here is the nature of the dark matter we can see through its gravitational effects in cosmological nature – we know it’s there, but we don’t know what it is.”

"So much of the dark Universe is still a huge mystery, but dark matter is something we can actively experimentally look for in the laboratory, and that’s what makes this project so exciting."

Professor Hiranya Peiris with the Northumberland Telescope at the Institute of Astronomy. Credit: Lloyd Mann

Professor Hiranya Peiris with the Northumberland Telescope at the Institute of Astronomy. Credit: Lloyd Mann

ALPHA is a collaboration between 12 institutions: Yale University (which is hosting the experiment); Arizona State University; University of California, Berkeley; University of Cambridge; University of Colorado at Boulder; University of Iceland; ITMO University; Johns Hopkins University; MIT; Oak Ridge National Laboratory; Stockholm University, and Wellesley College.

It is funded by the Simons Foundation and the John Templeton Foundation, which along with the Gordon and Betty Moore Foundation and the Alfred P. Sloan Foundation have partnered to fund 11 innovative table-top experiments, many of which will explore realms of physics typically probed by large-scale facilities. The foundations have pledged a total of £24m ($30m) over five years.

In Cambridge, scientists from the Cavendish Laboratory and the Institute of Astronomy will support the project by providing R&D testing for the superconducting resonator components.

Dr Siddharth Saxena, superconductivity specialist at the Cavendish Laboratory, said: “Our Cambridge team will support the design and development of the detection systems to make this table-top experiment cutting edge in its resolution and efficiency.”

Professor Mete Atatüre, Head of the Cavendish Laboratory, said: “By pooling their resources and expertise, the various foundations have boosted the impact of their support and are able to collectively fund more table-top projects that could push the frontiers of fundamental physics. This development is very timely for Cambridge, given the current interest in boosting dark matter science in the UK.”

And Professor Peiris believes the University’s role as a founding partner of the ALPHA project, along with other UK initiatives in this field – including ambitions to expand the Boulby Underground Laboratory in North Yorkshire – could help position the country at the heart of dark matter detection.

“The UK could become a leader in dark matter experimentation,” she said. “We are heavily involved in international facilities, where we do a lot of work on experiments happening in other countries, but it would be really nice to do more of those experiments here.

“Dark matter is a huge puzzle to solve, and for me that’s the motivation. Any time nature is telling us ‘look here, there’s a huge mystery to solve’, scientists have picked at it and have made big discoveries that have changed our thinking.

“But there’s also the experimental side of it, and developing this type of state-of-the-art equipment which can have different applications. Quantum technology is making great leaps forward and will be crucial in solving some of the big technological challenges for humanity.”

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