Scientists working on the Muon g-2 experiment, hosted by the U.S. Department of Energy’s Fermi National Accelerator Laboratory, have released their third and final measurement of the muon magnetic anomaly.
The Muon g-2 experiment gets its name from this relation.
So physicists decided to upgrade the Muon g-2 experiment to make a more precise measurement.
After years of significant upgrades and improvements, the Fermilab Muon g-2 experiment started up on May 31, 2017.
The Muon g-2 collaboration is made up of nearly 176 scientists from 34 institutions in seven countries.
Researchers engaged in the U.S.-hosted Muon g-2 experiment. S. The Fermi National Accelerator Laboratory of the Department of Energy has published its third and last measurement of the muon magnetic anomaly. This figure is associated with the experiment’s namesake measurement, g-2. The final result exceeds the initial experimental design goal of 140 parts per billion and is in agreement with their published results from 2021 and 2023, but with a much higher precision of 127 parts per billion.
A sensitive test of the Standard Model of particle physics is provided by the muon’s anomalous magnetic moment, or g–2. It’s wonderful to see an experiment conclude definitively with a precise measurement, and this is an exciting result,” Regina Rameika, the U. S. . Associate Director for the Office of High Energy Physics, Department of Energy.
This long-awaited outcome is a remarkable precision accomplishment and will continue to be the most accurate measurement of the muon magnetic anomaly in the world for many years to come. This finding offers a strict standard for suggested extensions of the Standard Model of particle physics, even in the face of recent difficulties with the theoretical predictions that diminish evidence of new physics from muon g-2.
Argonne National Laboratory physicist Peter Winter, co-spokesperson for the Muon g-2 collaboration, said, “This is a very exciting moment because we not only achieved our goals but exceeded them, which is not very easy for these precision measurements.”. “Overall, it has been very successful with the help of the funding agencies and the host lab, Fermilab, as we have achieved or exceeded almost all of our goals. “”.
Lawrence Gibbons, a professor at Cornell University and the analysis co-coordinator for this result, stated that g-2 has been teaching us a lot about the nature of nature for more than a century. It’s thrilling to include an exact measurement that, in my opinion, will last for ages. “.”.
The experiment known as Muon g-2, or “gee minus two,” examines the wobble of the muon, a fundamental particle. Similar to electrons but roughly 200 times more massive, muons share a quantum mechanical characteristic known as spin, which they can think of as a tiny internal magnet. When an external magnetic field is present, the internal magnet will precess, or wobble, like the axis of a spinning top.
The g-factor is a number that describes the muon’s properties and determines the precession speed in a magnetic field. Based on the Standard Model of particle physics, which contains the current understanding of the universe’s fundamental functioning, theoretical physicists compute the g-factor.
It was estimated that g would be 2 almost a century ago. However, experimental measurements quickly revealed that g was somewhat different from 2 by a quantity called the muon’s magnetic anomaly, aμ, which was computed using (g-2)/2. This relationship is the source of the name for the Muon g-2 experiment.
The effects of all Standard Model particles are encoded in the muon magnetic anomaly, and theoretical physicists are able to compute these contributions with remarkable accuracy. However, earlier measurements made at Brookhaven National Laboratory in the late 1990s and early 2000s suggested that there might be a difference between the theoretical calculation at the time and actual data.
Experiments that deviate from theory may point to new physics. In particular, scientists questioned whether this disparity might be brought on by particles that haven’t been found yet tugging at the muon’s precession.
Therefore, in order to make a more accurate measurement, physicists upgraded the Muon g-2 experiment. The magnetic storage ring at Brookhaven was moved from Long Island, New York, to Fermilab in Batavia, Illinois, in 2013. On May 31, 2017, following years of major enhancements and modifications, the Fermilab Muon g-2 experiment went online.
Concurrently, the Muon g-2 Theory Initiative was established by a global group of theorists to enhance the theoretical computation. The Theory Initiative released an updated, more accurate Standard Model value in 2020 using a method that incorporates input data from additional experiments.
When Fermilab revealed its first experimental result in 2021, confirming the Brookhaven result with a marginally higher degree of precision, the difference with the result from that technique grew even more. Simultaneously, a new theoretical prediction based on a second method that significantly uses computing power was released. This new figure reduced the disparity because it was nearer the experimental measurement.
Combining the findings of multiple groups that employed the novel computational method, the Theory Initiative recently released a new prediction. The possibility of new physics is dampened by this result, which stays closer to the experimental measurement. Nonetheless, the theoretical endeavor will persist in its endeavor to comprehend the disparity between the computational and data-driven approaches.
This is the most recent experimental value of the muon’s magnetic moment from the Fermilab experiment.
aμ = (g-2)/2 (muon, experiment) = 0.001 165 920 705 +- 0.000 000 000 114 (stat. ().
minus 0.000000000091 (syst. ().
The last three years’ worth of data, collected between 2021 and 2023, along with the previously released datasets, served as the basis for this final measurement. The dataset used for their second result in 2023 was more than tripled in size as a result, and the collaboration was able to ultimately meet their precision target set in 2012.
It also serves as an analysis of the highest-quality data from the experiment. As their second data collection run came to a close, the Muon g-2 collaboration completed experiment modifications and improvements that enhanced the muon beam’s quality and decreased uncertainties.
In a paper submitted today to Physical Review Letters, the Muon g-2 collaboration details the outcome.
“The muon’s magnetic moment remains a strict test of the Standard Model, as it has for decades,” said Simon Corrodi, an analysis co-coordinator and assistant physicist at Argonne National Laboratory. The new experimental finding clarifies this basic theory and will serve as a standard for future theoretical computations. “”.
The muon magnetic anomaly will probably be measured again in the early 2030s by an experiment at the Japan Proton Accelerator Research Complex, although for the time being it won’t be as precise as Fermilab.
The inconsistency between their two theoretical predictions will be addressed by the Theory Initiative in the interim.
Nearly 176 scientists from 34 institutions across seven countries comprise the Muon g-2 collaboration. The international nature of the partnership was crucial to the experiment’s success, according to Marco Incagli, a physicist with the Italian National Institute for Nuclear Physics at Pisa and co-spokesperson for Muon g-2.
Surprisingly, the scientists come from a range of physics specialties. According to Incagli, “this experiment is pretty strange because it contains very different ingredients.”. It is actually carried out through cooperation between communities that typically work on various experiments. “”.
Muon g-2 required more than just high-energy physicists, in contrast to other high-energy physics experiments; accelerator physicists, atomic physicists, and nuclear physicists are also part of the collaboration. “When all these different experts came together, we were able to solve problems that probably one group could not have done alone, which was very valuable to see,” Incagli said.
There is still more to be gleaned from the six years of Muon g-2 data, even though the primary analysis of the experiment is now complete. Tests of charge, parity, and time-reversal symmetry—three essential properties of physical laws—as well as measurements of the muon’s electric dipole moment will be the results of the upcoming collaboration.
Gibbons described the experiment as “incredibly beautiful.”. “The information that is revealed is truly brilliant. Accessing and analyzing this data has been an honor. “”.
Winter, who has been involved in the collaboration since 2011, stated, “Of course, it’s sad to end such an endeavor because it’s been a large part of many of our collaborators’ lives.”. However, in order to further the field in other directions, we also wish to move on to the next physics that is available.
Winter continued, “I believe it will be a textbook experiment that will be a lasting reference for many future decades to come.”.
