The Muon g-2 Collaboration has doubled the precision of their 2021 measurement of the muon’s magnetic moment and it disagrees with the predictions based on the standard model of physics. Muons are similar to electrons, but 207 times more massive. They are also unstable: they are created in particle collisions and decay into their lighter cousins shortly afterwards.
The numbers shared two weeks ago in Liverpool—and today with the world—are the latest update in a decades-long effort to tease out the exact values of the muon’s magnetic moment and its “g-factor”. The magnetic moment of a particle—a measure of the torque exerted on it by a magnetic field—is proportional to the particle’s charge and spin via a dimensionless parameter called the g-factor.
In a hypothetical world where the muon behaves as an isolated, idealized point particle, its g-factor will equal 2. In the real world, where the muon constantly interacts with other “virtual” particles flashing in and out of existence, its g-factor is slightly larger than 2. The difference between real and hypothetical values—the so-called g − 2 anomaly—arises because the virtual particles modify the effective charge of the muon and the speed at which its spin rotates in a magnetic field. The Muon g-2 experiments measure this speed and use it to determine the muon’s magnetic moment and the g−2 anomaly.
Calculations based on the standard model of particle physics currently predict that the muon has a g-factor of 2.00233183620(86).
The new experimental value is 2.00233184110(48) is twice as precise as the 2021 figure and the statistical significance of the discrepancy has jumped to 5 sigma or, if the earlier results are averaged together with the new ones, 5.2 sigma.
The new uncertainty now standing at 0.20 [parts per million].
Recalculating the Standard Model G Factor Might Eliminate the Difference
Results by Fodor and his colleagues in 2021, an alternative technique for calculating g – 2 has emerged, which does not require collider data and instead uses computer simulations. When the Muon g – 2 measurement is compared against this new prediction, the discrepancy essentially disappears. Several other teams have followed up with their own computer simulations, which have tentatively converged with those by Fodor’s group.
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No, we cannot even boil water with muons, but the models now agree on the number 2 to an arbitrary precision.
I don’t know, man, if you accelerate a stream of muons into a water target, it will *probably* boil, eventually, depending on the energy of the muons and the size of the target.
Well, if they could beam them, that would be useful, wouldn’t it?
They’re kinda phantom particles that exist briefly after high energy collisions from what I’ve read, so – they don’t really *exist*, and thus unable to boil water.