A rare particle decay recorded at CERN’s Large Hadron Collider could point to dark matter, but the result is short of a discovery, and the UK funding for the next upgrade has been withdrawn
Scientists led from Cambridge have picked up signals from the smallest scale of nature yet probed, about 100 billion times smaller than an atom, in data from the Large Hadron Collider (LHC). Some physicists call this realm the “zeptoverse”. The measurement, made by the LHCb experiment at CERN, could help build a more complete theory of how the Universe works and potentially help detect dark matter. It is evidence of an exceptionally rare process, not a confirmed discovery. The research has also reopened a row over the UK’s decision to pull funding for the experiment’s next upgrade.
What the experiment saw
The LHC, at CERN on the Swiss-French border, smashes particles together at high energy so researchers can study the debris. One product is the beauty quark, a sub-atomic particle that exists for only one and a half trillionths of a second before decaying. Despite that, the team detected it interacting with other tiny particles at a scale of a billion-trillionth of a metre.
Some theories suggest particles are more sensitive to dark matter at these scales, and that it could affect how quarks interact and decay. Dark matter makes up a large part of the cosmos and is known only through its gravitational pull on ordinary matter. “We’re knocking on the door of this zeptoverse,” said Dr Harry Cliff, of Cambridge University, who led the analysis. He said the work gave researchers a “ringside seat” to the behaviour of possible new particles.
The Times reported the result has a statistical significance of 3.2 sigma, below the five sigma that particle physicists normally require to claim a discovery. The team found about a dozen candidate events in ten years of collision data, in a process expected roughly once in every ten billion relevant decays. It involves a beauty meson turning into two muons, heavier relatives of the electron. No dark matter particle has been detected. Researchers are looking for subtle effects that unknown particles might have on known interactions, and a rare decay does not by itself show dark matter is responsible.
CERN reported separate results on 14 October from its CMS and LHCb experiments, which both found small differences from theoretical predictions in related beauty-quark decays. CERN cautioned they remain inconclusive.
Funding row
“What we need is more data,” Dr Cliff said. Countries in the collaboration have agreed a £150m upgrade of the LHCb detector that would increase the frequency of these decays tenfold. UK Research and Innovation (UKRI), the government funding body, has withdrawn its share. It did so as it announced cuts to other particle physics and astronomy projects, including Jodrell Bank’s Lovell telescope, despite a record rise in the overall science budget.
Physicist Matt Kenzie wrote in a Cambridge publication that the UK’s planned contribution was £49.4m over ten years, with about £5m already spent. On 2 November science minister Chris McDonald told the Commons the project had been turned down through both UKRI’s Infrastructure Fund and the Science and Technology Facilities Council’s prioritisation exercise. He said the existing LHCb experiment and CERN work continue to be funded.
Prof Tim Gershon, who leads the LHCb collaboration, said the UK’s full involvement was in doubt. “The UK is at risk of not being involved and making really major discoveries,” he said. “But I think the biggest long-term impact comes from the fact that the UK won’t get the benefits from training young people who really are our greatest product.” Dr Mary Richardson-Slipper, who worked on the result, said she was looking for jobs abroad “because that seems to be where there are more opportunities at the moment”.
Prof Brian Cox, of the University of Manchester, who was not part of the team, called the result “important” but described the funding decision as “extraordinary”, saying: “It would be extraordinary to walk away from UK scientific leadership at this moment, damaging the future research programme and seriously damaging our hard-won international reputation.”
UKRI said it remained fully engaged with CERN as its second largest funder, at around £175m a year. A spokesperson said: “We sought independent advice and have taken forward an exciting portfolio of new infrastructure investments, which include projects in clean energy, medical imaging and cultural heritage. However, as usual, there were more exciting applications for funding than we were able to support.”
The Institute of Physics has warned that cancelling the upgrade could cost UK suppliers: the previous upgrade generated about £15m in contracts for more than 80 British firms.
