If you were to ask physicists what they considered the most accurate and successful equation in their field, chances are more than a few would say it’s Dirac’s equation, which describes the relativistic quantum theory of the electron. Their work builds on a single equation published in 1928 that simultaneously started the field of quantum electrodynamics and laid the foundations for the Muon g-2 experiment. “We’ve not had a theory effort like this before in which all the different evaluations are combined into a single Standard Model prediction,” said Aida El-Khadra, a physicist at the University of Illinois and co-chair of the Steering Committee for the Muon g-2 Theory Initiative, the name of the group of scientists who worked on the calculation. This theoretical value, published in the arXiv, is the result of over three years of work by 130 physicists from 78 institutions in 21 countries. The most precise experimental result available so far is:Ī = (g-2)/2 (muon, expmt) = 116 592 089(63) x 10 -11Īgain, the slight discrepancy between the experimental measurements and the predicted value has persisted, and again it is just beneath the threshold to make a definitive statement.
The theoretical value of the anomalous magnetic moment of the muon, published today, is:Ī = (g-2)/2 (muon, theory) = 116 591 810(43) x 10 -11 At the same time, theorists worked to improve the precision of their calculations and fine-tune their predictions. The decades-long effort eventually led to an experiment at Brookhaven National Laboratory and its successor at Fermilab, as well as plans for a new experiment in Japan. Since then, experimenters have continued to quantify that wobble, making more and more precise measurements of the muon’s anomalous magnetic moment. In the late 1960s at CERN laboratory, scientists began using a large circular magnetic ring to test the theory that described how muons should “wobble” when moving through a magnetic field. Now the world awaits the result from Fermilab’s current Muon g-2 experiment, whose magnetic storage ring is pictured here. Today’s publication by the Muon g-2 Theory Initiative marks the first time the global theoretical physics community has come together to publish a consensus value for the muon’s magnetic moment. Depending on how much the Standard Model theoretical calculation differs from the upcoming experimental measurement, physicists may be one step closer to determining whether the muon’s magnetic interactions are hinting at particles or forces that have yet to be discovered. In the upcoming months, physicists working on the experiment will unveil their preliminary measurement for the value.
Now the world awaits the result from Fermilab’s current Muon g-2 experiment. The result differs from the most recent experimental measurement, which was performed at Brookhaven National Laboratory in 2004, but not significantly enough to unambiguously answer this question. While a number of international groups have worked separately on the calculation, this publication marks the first time the global theoretical physics community has come together to publish a consensus value for the muon’s magnetic moment.
The magnetic moment of subatomic particles is generally expressed in terms of the dimensionless Landé factor, called g. This week, an international team of more than 170 physicists published the most reliable prediction so far for the theoretical value of the muon’s anomalous magnetic moment, which would account for its particular rotation, or precession. For decades, scientists studying the muon have been puzzled by a strange pattern in the way muons rotate in magnetic fields, one that left physicists wondering if it can be explained by the Standard Model - the best tool physicists have to understand the universe.
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