Scientists probe ‘fifth force of nature’ as ‘exciting’ breakthrough could rewrite physics

Large Hadron Collider: Inside world’s largest particle collider

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The first “tantalising evidence” of this new force was published in March this year, using data collected by the world’s biggest particle collider. Although the news was met with a great deal of fanfare, scientists said they were only “cautiously optimistic” about the results and their potential repercussions. But new evidence has emerged to give the theory more credence and that threatens to completely shake up our understanding of the subatomic world.

According to the so-called Standard Model of particle physics, the world is governed by four fundamental forces.

These are the strong force, the weak force, the electromagnetic force and the gravitational force.

Harry Cliff, a particle physicist at the University of Cambridge, has described the Standard Model as “the most successful scientific theory ever written down”.

But there is a growing body of evidence to suggest the model needs to be updated, if not outright completely rewritten.

Discoveries at the 17-mile-long (27km) LHC, which runs deep under parts of France and Switzerland, suggest there is a fifth force that could explain irregularities in the decay of certain particles.

The Standard Model predicts particles known as beauty quarks (bottom quarks) equally decay into electrons and the heavier muon particles.

Dr Cliff said: “Beauty quarks are unstable, living on average just for about 1.5 trillionths of a second before decaying into other particles.

“The way beauty quarks decay can be strongly influenced by the existence of other fundamental particles or forces.

“When a beauty quark decays, it transforms into a set of lighter particles, such as electrons, through the influence of the weak force.”

But the LHCb experiment at The European Organization for Nuclear Research (CERN) appears to have found an irregularity in this decay, with the beauty quarks decaying into other particles, possibly as a result of an unknown external force.

The LHCb is one of the four colossal experiments stationed along the LHC’s circular tunnel, where physicists collide particles at near the speed of light to break them down to their constituent parts.

The March paper found beauty quarks detected at the LHCb were decaying into electrons and muons at different rates.

Dr Cliff said this was an unexpected result as the muon is virtually a clone of the electron except for being 200 times heavier.

According to the expert, all of the known forces should pull on the electrons and muons with equal strength when decaying.

Instead, Dr Cliff and his colleagues have observed the muon decay only occurred about 85 percent as often as electron decay.

The physicist, who discussed the results in an article for The Conversation, said: “Assuming the result is correct, the only way to explain such an effect would be if some new force of nature that pulls on electrons and muons differently is interfering with how beauty quarks decay.

“The result caused huge excitement among particle physicists.

“We’ve been searching for signs of something beyond the standard model for decades, and despite ten years of work at the LHC, nothing conclusive has been found so far.”

The discovery of a new force, he added, would be a “huge deal” and could potentially solve some of the fundamental mysteries of the cosmos like dark matter.

But there is a major caveat: the results have not yet been determined conclusively.

So far, the results have come within a degree of “error” of about one in 1,000.

Particle physicists refer to this result as being “three sigma” and in practical terms, they are still a way off from confirming their discovery.

But the LHCb researchers are confident they have made progress since their paper was originally published in March and are getting closer to cracking the decay irregularities.

Their latest results show muon decays only happened about 70 percent as often as electron decay.

Their theories won’t be confirmed until the uncertainty in results is narrowed down to five sigma – less than a one in a million chance of the data being a statistical anomaly.

One way of doing this is to simply collect more data at the giant experiment.

The LHC is also being upgraded, which will help collect more accurate measurements in the future.

Dr Cliff said: “My colleagues are currently working hard to squeeze as much information as possible out of the existing data, while busily preparing for the first run of the upgraded LHCb experiment.

“Meanwhile, other experiments at the LHC, as well at the Belle 2 experiment in Japan, are closing in on the same measurements.

“It’s exciting to think that in the next few months or years a new window could be opened on the most fundamental ingredients of our universe.”

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