Science & Technology

Exciting new physics evidence from the US Department of Energy’s Muon G-2 experiment – ​​”Today is a special day”

The· The long-awaited The first results of the muon g-2 experiment at the Fermi National Accelerator Laboratory of the U.S. Department of Energy show that a basic particle called a muon is not predicted by the standard model of particle physics, which is the best theory of scientists. Shows that it works with. Created with unprecedented precision, this groundbreaking result supports a contradiction that has been bitten by researchers for decades.

Strong evidence that muons deviate from the Standard Model calculation may suggest exciting new physics. Muons act as windows to the world of elementary particles and may interact with particles and forces that have not yet been discovered.

Graziano Venanzoni, co-spokesman and physicist for the Muong-2 experiment at the Italian National Institute of Nuclear Physics, said: “It is a great achievement to the young researchers who have made it possible to achieve this wonderful result with talent, ideas and enthusiasm.”

Muong-2 experiment at Fermi laboratory

The first results of the Muong-2 experiment at the Fermi Institute strengthened the evidence of new physics. The centerpiece of the experiment is a 50-foot-diameter superconducting magnetic storage ring in a detector hall surrounded by electronics racks, muon beamlines, and other equipment. This striking experiment operates at 450 degrees Fahrenheit and studies precession (or wobbling) as muons pass through a magnetic field. Credits: Reidar Hahn, Fermilab

Muons are about 200 times larger than their cousin, the electron. Muons occur naturally when cosmic rays hit the Earth’s atmosphere, and the Fermi Institute’s particle accelerators can produce them in large quantities. Like an electron, a muon behaves as if it had a small internal magnet. In a strong magnetic field, the direction of the muon’s magnet is precession, or wobbling, like the axis of a spinning top or gyroscope. The strength of the internal magnet determines the speed at which muons precess in an external magnetic field and is expressed by a number that physicists call the g-factor. This number can be calculated with super high accuracy.

Since muons circulate in the Muong-2 magnet, they also interact with the quantum bubbles of subatomic particles that fly out of and out of existence. Interactions with these short-lived particles affect the value of g-factor, accelerating or slowing muon precession very slightly.The· Standard model This so-called anomalous magnetic moment is predicted very accurately. However, if the quantum foam contains additional forces or particles not described in the Standard Model, further fine-tune the muon’s g-factor.

“This amount we measure reflects the interaction of muons with everything else in the universe, but theorists use all the known forces and particles of the Standard Model to make the same amount. If you calculate, you won’t get the same answer, “said Lenny Fatemi, a physicist at the University of Kentucky and a simulation manager for muons. g-2 experiment. “This is strong evidence that muons are sensitive to something that is not in our best theory.”

A predecessor experiment at DOE’s Brookhaven National Laboratory, completed in 2001, suggested that muon behavior did not match the Standard Model. The new measurements from the Muong-2 experiment at Fermilab are in strong agreement with the values ​​found at Brookhaven, which is different from the theory using the most accurate measurements to date.

Muong-2 result plot

The first results of the Muong-2 experiment at Fermilab corroborate the results of an experiment conducted at Brookhaven National Laboratory 20 years ago. Together, the two results provide strong evidence that muons deviate from the Standard Model’s predictions.Credits: Ryan Postel, Fermilab / Muong-2 collaboration

The allowable theoretical values ​​of muons are as follows.
G-factor: 2.00233183620 (86)
Anomalous magnetic moment: 0.00116591810 (43)
[uncertainty in parentheses]

The results of the new experimental world average announced today by the Muong-2 collaboration are as follows:
G-factor: 2.00233184122 (82)
Anomalous magnetic moment: 0.00116592061 (41)

Combining the results of Fermilab and Brookhaven, the significance of 4.2 sigma shows the difference from theory. This is a compelling proof of the new physics, with a little embarrassment of the 5 sigma (or standard deviation) that scientists need to claim their discoveries. The chances of the result being statistical variation are about 1 in 40,000.

The Fermilab experiment reuses a 50-foot-diameter superconducting magnetic storage ring, which is the main component of the Brookhaven experiment. In 2013, it was transported 3,200 miles by land and sea from Long Island to the outskirts of Chicago, where scientists could use Fermilab’s particle accelerator to generate the most powerful muon beam in the United States. Over the next four years, the researchers assembled the experiment. Adjusted and calibrated an incredibly uniform magnetic field. We have developed new technologies, instrumentation and simulations. We thoroughly tested the entire system.

The muon g-2 experiment sends muon beams to storage rings, where they circulate thousands of times at near the speed of light. The detectors that line the ring allow scientists to determine the speed of muon precession.

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

“I’m very happy that we’ve finally solved this mystery 20 years after the Brookhaven experiment,” said Brookhaven, co-spokesperson for the current experiment.

Data analysis for the second and third runs of the experiment is in progress, the fourth run is in progress, and the fifth run is planned. Combining the results of all five runs, scientists can more accurately measure muon wobble and more reliably reveal whether new physics are hidden in quantum bubbles.

“So far, we have analyzed less than 6% of the data finally collected in the experiment. These first results show interesting differences from the standard model, but in the next few years. You’ll learn a lot more, “says Polly.

“Identifying the subtle behavior of muons is an amazing achievement that will guide the quest for physics beyond the Standard Model over the next few years,” said Joe Ricken, Deputy Director of Research at Fermilab. “This is an exciting time for particle physics research, and Fermilab is at the forefront.”

Reference: B. Abi et al. “Measurement of positive muon anomalous magnetic moments up to 0.46 ppm” by. (Muon g-2 collaboration), April 7, 2021 Physical review letter..
DOI: 10.1103 / PhysRevLett.126.141801

The Muon g-2 experiment is supported by the US Department of Energy. National Science Foundation (USA); Istituto Nazionale di Fisica Nucleare (Italy); Science and Technology Facilities Council (UK); Royal Society (UK); European Union Horizon 2020; China National Natural Science Fund; MSIP, NRF and IBS-R017 -D1 (Republic of Korea); And the German Research Foundation (DFG).

Fermi Lab is one of the leading national laboratories in the United States for particle physics research. Fermilab, a US Department of Energy Institute of Science laboratory, is located near Chicago, Illinois and operates under a contract with the Fermi Research Alliance LLC.

The DOE Department of Science is the largest supporter of basic research in the US physical sciences and is working to address some of the most pressing challenges of our time.

[Editor’s Note: Today a different group of researchers announced very different results, concluding that the muon’s magnetic field aligns with the standard model of particle physics.]

Exciting new physics evidence from the US Department of Energy’s Muon G-2 experiment – ​​”Today is a special day” Exciting new physics evidence from the US Department of Energy’s Muon G-2 experiment – ​​”Today is a special day”

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