New muon measurements could rewrite particle physics | Smart News

The 50-foot-wide hippodrome used to study muons traveled by barge around Florida and Mississippi, then by truck through Illinois.
Reidar Hahn, Fermilab

About 50 years ago, physicists came up with a rulebook to describe how fundamental particles interact to create the world as we know it. Since then, researchers have pushed this theoretical framework, called the Standard Model, to its limits in order to study its imperfections.

Today, the results of two particle physics experiments come close to uncovering a gap in the Standard Model.

The experiments focused on muons, which are similar to electrons. Both have electric charge and spin, causing them to oscillate in a magnetic field. But muons are more than 200 times larger than electrons, and they split into electrons and another particle, neutrinos, in 2.2 millionths of a second. Luckily, that’s just enough time to collect accurate measurements, with the right equipment, like a 50-foot-wide magnetic circuit.

Physicist Chris Polly of the Fermi National Accelerator Laboratory presented a graph at a seminar and press conference last week that showed a discrepancy between the theoretical calculation and actual measurements of muons moving through the racetrack.

“We can say with pretty high confidence that there has to be something contributing to that white space,” Polly said at the press conference, according to Dennis Overbye at the New York Times. “What monsters could be hiding there?”

The Standard Model aims to describe everything in the universe in terms of its fundamental particles, like electrons and muons, and its fundamental forces. The model predicted the existence of the Higgs boson particle, which was discovered in 2012. But physicists know that the model is incomplete: it takes into account three fundamental forces, but not gravity, for example.

A disconnect between theory and experimental results could help researchers uncover hidden physics and extend the Standard Model to more fully explain the universe.

“New particles, new physics could be just beyond our search,” Wayne State University particle physicist Alexey Petrov tells The Associated Press’ Seth Borenstein. “It’s tantalizing.”

The Standard Model requires such complex calculations that it took a team of 132 theoretical physicists, led by Aida El-Khadra, to come up with its prediction for the muon oscillation in the Fermi Lab experiment. The calculations predicted an oscillation lower than that measured by the Fermilab experiment.

This week’s results closely follow new findings from the Large Hadron Collider. Last month, LHC researchers showed a startling rate of particles left over after breaking up high-speed muons.

“The LHC, if you will, is almost like crashing two Swiss watches against each other at high speed. The debris comes out and you try to piece together what’s inside,” University of Manchester physicist Mark Lancaster, who worked on the Fermilab experiments, tells Michael Greshko at National geographic. At Fermilab, “we have a Swiss watch, and we look at it very, very, very, very carefully and precisely, to see if it does what we expect it to do. »

The Fermilab group used the same 50-foot-wide ring that was first used in the 2001 muon experiments. The researchers shoot a particle beam into the ring, where the particles are exposed to magnets superconductors. The beam particles decay into several other particles, including muons. Then those muons swirl around the racetrack several times before decaying, giving physicists a chance to measure how they interact with the magnetic field, writes Daniel Garisto for American Scientist.

To avoid bias, the instruments the researchers used to measure muons gave encrypted results. The key – a number written on a piece of paper and hidden in two offices at Fermilab and the University of Washington – remained secret until a virtual meeting in late February. When the key was entered into the spreadsheet, the results became clear: the experiment did not match the theory.

“We were all really ecstatic, excited, but also shocked, because deep down I think we’re all a bit pessimistic,” Fermilab physicist Jessica Esquivel tells National geographic.

If the results hold as more data from the experiment emerges, they would upend “every other calculation made” in the field of particle physics, says David Kaplan, a theoretical physicist at Johns Hopkins University. , to the Associated Press.

Freya Blekman, a physicist from the Free University of Brussels, who did not take part in the work, says National geographic that the work “is Nobel-worthy, no doubt,” if it holds up.

Results to date should be published in journals Physical examination letters, A&B physical examination, Physical examination A and physical examination d. These results come from only six percent of the data that the Fermilab experiment expects to collect. Between this six percent and the experimental results from 2001, there is a one in 40,000 chance that the difference between theory and experiment is in error.

“It’s strong evidence that the muon is sensitive to something that’s not in our best theory,” says University of Kentucky physicist Renee Fatemi. New York Times.

But particle physics demands that researchers bring that down to a one in 3.5 million chance. The research team could have the final results by the end of 2023.

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