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The first results from Fermilab’s Muon g-2 experiment reinforce the proof of the new physics

The first results from the Muon g-2 experiment hosted at the Fermi National Accelerator Laboratory show that fundamental particles called muons behave in a way that is not predicted by the standard model of particle physics. These results confirm a previous experiment of the same name conducted at Brookhaven National Laboratory. In combination, the two results show strong indications that our best theoretical model of the subatomic world is incomplete. One possible explanation would be the existence of undiscovered particles or forces.

CHICAGO, April 7, 2021 / PRNewswire / – The long-awaited first results from the Muon g-2 experiment at the US Department of Energy’s Fermi National Accelerator Laboratory show that fundamental particles called muons behave in a way that is not predicted by the best theory of scientists, the standard model physics particles. This landmark result, made with unprecedented precision, confirms a mismatch that has irritated researchers for decades.

Strong indications that muons deviate from the standard model calculation may suggest exciting new physics. Muons act as a window into the subatomic world and could interact with particles or forces that have not yet been discovered.

“Today is a wonderful day, which we have been waiting for a long time not only for ourselves but for the entire international physics community,” said Graziano Venanzoni, co-representative of the Muon g-2 experiment and physicist at the Italian National Institute of Nuclear Physics. . “Great credit to our young researchers, who, with their talent, ideas and enthusiasm, have enabled us to achieve this incredible result.”

A muon is about 200 times larger than its cousin, the electron. Monsoons occur naturally when cosmic rays hit the Earth’s atmosphere and particle accelerators at Fermilab can produce them in large numbers. Like electrons, muons act like they have a small internal magnet. In a strong magnetic field, the direction of the muon magnet precedes, or oscillates, resembling the axis of a rotating peak or gyroscope. The strength of the inner magnet determines the rate at which the muon causes an external magnetic field and is described by a number that physicists call the factor g. This number can be calculated with extremely high accuracy.

As muons circulate in the Muon g-2 magnet, they also interact with a quantum foam of subatomic particles coming in and out of existence. Interactions with these short-lived particles affect the value of factor g, causing the ions to accelerate or decelerate. The standard model accurately predicts this so-called abnormal magnetic moment. But if the quantum foam contains additional forces or particles that do not correspond to the standard model, this would further modify the g muon factor.

“This quantity we measure reflects the muon’s interactions with everything else in the universe. “But when theorists calculate the same amount, using all the known forces and particles in the standard model, we do not have the same answer.” Rene Fatemi, physicist at University of Kentucky and the simulation manager for the Muon g-2 experiment. “This is strong evidence that monogamy is sensitive to something that is not in our best theory.”

A previous experiment at the DOE Brookhaven National Laboratory, completed in 2001, suggested that the ions’ behavior differed from the standard model. The new measurement from the Muon g-2 experiment at Fermilab is completely in line with the value found in Brookhaven and deviates from the theory with the most accurate measurement to date.

Acceptable theoretical values ​​for muon are:
coefficient g: 2.00233183620 (86) [uncertainty in parentheses]abnormal magnetic moment: 0,00116591810 (43)

The new experimental results of the global average announced today by the Muon g-2 collaboration are:
coefficient g: 2.00233184122 (82)
abnormal magnetic moment: 0,00116592061 (41)

The combined results of Fermilab and Brookhaven show a difference with the theory of the significance of 4.2 sigma, a little shy of the 5 sigma (or standard deviations) that scientists claim to claim a discovery, but are still compelling evidence for new physics. The probability of the results being statistical variation is about 1 in 40,000.

The Fermilab experiment reuses the main component of the Brookhaven experiment, a superconducting 50-foot-diameter magnetic storage ring. In 2013, it traveled 3,200 miles by land and sea from Long Island to Chicago suburbs, where scientists could take advantage of the Fermilab particle accelerator to produce the strongest radius the United States. Over the next four years, the researchers assembled the experiment. tuned and calibrated an incredibly uniform magnetic field. developed new techniques, instruments and simulations. and thoroughly tested the entire system.

The Muon g-2 experiment sends a bundle of muons to the storage ring, where they circulate thousands of times almost at the speed of light. Detectors that align the ring allow scientists to determine how fast the muons come from.

In its first year of operation, in 2018, the Fermilab experiment collected more data than all previous g-factor muon experiments. With more than 200 scientists from 35 institutions in seven countries, the Muon g-2 collaboration has now completed the analysis of the motion of more than 8 billion miles from this first run.

“After 20 years since the end of the Brookhaven experiment, it is so gratifying that we are finally solving this mystery,” said the Fermilab scientist. Chris Polly, who is a co-representative of the current experiment and was a lead graduate student in the Brookhaven experiment.

Data analysis for the second and third run of the experiment is in progress, the fourth run is in progress, and a fifth run is scheduled. The combination of the results from all five tracks will give scientists an even more accurate measurement of muon oscillations, revealing with greater certainty whether new physics is hidden within quantum foam.

“So far we have analyzed less than 6% of the data that the experiment will eventually collect. “Although these first results tell us that there is an interesting difference with the Model Model, we will learn a lot more in the next two years,” said Paul.

“Detecting the fine behavior of muons is a remarkable achievement that will guide the search for physics beyond the model model for years to come,” said Fermilab, Deputy Director of Research. Joe Licken. “This is an exciting time to explore particle physics and Fermilab is at the forefront.”

Fermilab is America’s leading national laboratory for particle physics research. The lab of the US Department of Energy, Fermilab is nearby Chicago, Illinoisand operates under contract from Fermi Research Alliance LLC. Visit Fermilab’s website at and follow us on Twitter @Fermilab.

The DOE Office of Science is the single largest proponent of basic science research in the United States and tries to meet some of the most pressing challenges of our time For more information, visit

The Muon g-2 ring is located in its detector room between electronic shelves, the muon beam line and other equipment.  This impressive experiment operates at a negative 450 degrees Fahrenheit and studies the recession (or oscillation) of muons as they travel in the magnetic field.

The first result of the Muon g-2 experiment at Fermilab confirms the result of an experiment conducted at the Brookhaven National Lab two decades ago.  Together, the two results show strong indications that the muons deviate from the Standard Model prediction.

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