Thursday, August 5

Cern’s experiment points to a new force of nature | Large Hadron Collider


Scientists at the Large Hadron Collider near Geneva have detected an unusual signal in their data that may be the first indication of a new kind of physics.

The LHCb collaboration, one of the LHC’s four major teams, analyzed 10 years of data on how unstable particles called B mesons, created momentarily in the vast machine, disintegrated into more familiar matter, such as electrons.

The mathematical framework that underpins scientists’ understanding of the subatomic world, known as the Standard Model of particle physics, strongly holds that particles must decompose into products that include electrons at exactly the same rate as into products that include a heavier prime. . of the electron, a particle called a muon.

But results published by Cern Tuesday they suggest something unusual is happening. The B mesons are not decaying the way the model says they should: instead of producing electrons and muons at the same rate, nature seems to favor the path that ends with electrons.

“We would expect this particle to decay into the electron-containing end state and the end state continues muons at the same rate as the others,” said Professor Chris Parkes, an experimental particle physicist at the University of Manchester and spokesperson for the LHCb collaboration. “What we have is an intriguing clue that perhaps these two processes are not happening at the same rate, but it is not conclusive.”

In the language of physics, the result has a significance of 3.1 sigma, which means that the probability of it being a fluke is approximately one in 1,000. While that may sound like compelling evidence, particle physicists tend not to claim a new discovery until a result reaches five sigma significance, where the chance of it being a statistical quirk drops to one in a few million.

“It’s an intriguing track, but we’ve seen sigmas come and go before. It happens surprisingly often, ”Parkes said.

The Standard Model of Particle Physics describes the particles and forces that govern the subatomic world. Built over the last half century, it defines how elementary particles called quarks build protons and neutrons within atomic nuclei, and how these, usually combined with electrons, form all known matter. The model also explains three of the four fundamental forces of nature: electromagnetism; the strong force, which holds the atomic nuclei together; and the weak force that causes nuclear reactions in the sun.

But the standard model does not describe everything. It does not explain the fourth force, gravity, and perhaps most surprisingly, it says nothing about the 95% of the universe that physicists believe is not built from normal matter.

Much of the cosmos, they believe, consists of dark energy, a force that appears to be driving the expansion of the universe, and dark matter, a mysterious substance that appears to hold the cosmic web of matter in place like an invisible skeleton.

“If it turns out that with additional analysis of additional processes, we could confirm this, it would be extremely exciting,” said Parkes. It would mean that there is something wrong with the standard model and that we need something additional in our fundamental theory of particle physics to explain how this would happen. “

Despite the uncertainties about this particular result, Parkes said that when combined with other results in B mesons, the case for something unusual to happen became more compelling.

“I would say there is a cautious emotion. We are intrigued that this result is not only quite significant, it fits the pattern of some previous LHCb results and other experiments around the world, ”he said.

Ben Allanach, professor of theoretical physics at the University of Cambridge, agrees that, along with other findings, the latest LHCb result is exciting. “I really think this will turn into something,” he said.

If the result turns out to be true, it could be explained by the hitherto hypothetical particles called Z primes or leptoquarks that bring new forces to other particles.

“There could be a new quantum force causing the B mesons to break into muons at the wrong rate. It is bringing them together and preventing them from breaking down into muons at the rate we would expect, ”Allanach said. “This force could help explain the peculiar pattern of the masses of different particles of matter.”

Scientists will collect more data from the LHC and other experiments around the world, such as Belle II in Japan, in hopes of confirming what is happening.


www.theguardian.com

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