Restarting the Large Hadron Collider and searching for a fifth force of nature

by time news

The Large Hadron Collider (LHC) will resume on Friday after a three-year hiatus, expected to solve a scientific problem about whether a mysterious anomaly could indicate the existence of a fifth fundamental force of nature.

The puzzling results reported last year have reignited hopes that the 20-mile-long collider could make a second huge discovery, more than a decade after the Higgs boson.

Dr Mitch Battle, a particle physicist at Imperial College London whose team was responsible for last year’s research, said: “We are going into this race with more optimism about the possibility of a revolution to come. Fingers intertwined.”

So far, everything that has been detected at the LHC – including the Higgs – is in line with the so-called Standard Model. This has been the guiding theory of particle physics since the 1970s, but is known to be incomplete because it fails to explain some of physics’ deepest mysteries, such as the nature of dark matter.

However, data collected in the LHCb experiment, one of four massive particle detectors at Cern in Switzerland, appears to show that the particles are behaving in a way that cannot be explained by the Standard Model.

The experiment looked at the decay of particles called beauty quarks, which are expected to decay at an equal rate into electrons and their heavier cousins, muons. However, beauty quarks appear to turn into muons about 15% less, indicating that an unknown factor – potentially a new force – was tipping the scales. Two of the top candidates include hypothetical force-carrying particles called leptoquarks, or Z primes.

“The stakes are very high,” Patel said. “If we confirm that, it will be a revolution of the kind we have not seen – certainly in my life. You don’t want to screw it up.”

Before shutting down the LHC for promotion in 2018, the team collected enough data to indicate that the odds were roughly a thousand to an outcome that occurs by chance. But the gold standard for particle physics is a much stricter one at a confidence level of 3.5 metres, which means more data is needed before the discovery is announced. There is also a long-standing possibility that some unknown experimental flaw could explain the results.

“When you show this result to particle physicists, their first instinct is, ‘You screwed up,’ rather than a new force of nature,” Patel said. “We physicists like to be above certainty and get out the other side.”

In the past year, the expectation has been raised by more intriguing hints of physics beyond the Standard Model seen in other experiments, including recent experiments with unexplained results from Fermilab in the US.

“It appears that there is a set of loose filaments now,” said Professor John Butterworth of University College London, who is working on the Atlas experiment of the Large Hadron Collider. “It made me start to think that there might be something within reach from this race or the next round.”

If the LHC fails to detect a new science beyond the Standard Model, Butterworth said, this would not represent a failure but would leave the field “a bit in a quandary” about where we should look next.

The third round is expected to run until 2026, after an upgrade that included the installation of additional powerful magnets designed to compress protons inside the collider into finer, denser beams. This will increase the rate of particle collisions inside the accelerator, which means that scientists will be able to monitor rare events with greater accuracy.

“The potential for discovering new ideas is still very large,” said Ashutosh Kotwal, an experimental particle physicist at Duke University in the US and co-chair of a research group on the Atlas experiment for the Large Hadron Collider. It’s worth noting that the data we’ve collected so far is no more than one-tenth of the total we’re planning on doing. It’s too early to lose heart.”

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