Why the name is g minus 2?

• It is called the g–factor, a measure that derives from the magnetic properties of the muon. Because the muon is unstable, scientists study the effect it leaves behind on its surroundings.
• Muons act as if they have a tiny internal magnet. In a strong magnetic field, the direction of this magnet “wobbles” — just like the axis of a spinning top. The rate at which the muon wobbles is described by the g-factor, the quantity that was measured. This value is known to be close to 2, so scientists measure the deviation from 2. Hence the name g–2.
• The g-factor can be calculated precisely using the Standard Model. In the g–2 experiment, scientists measured it with high-precision instruments. They generated muons and got them to circulate in a large magnet. The muons also interacted with a “quantum foam” of subatomic particles “popping in and out of existence”, as Fermilab described it. These interactions affect the value of the g-factor, causing the muons to wobble slightly faster or slightly slower. Just how much this deviation will be (this is called anomalous magnetic moment), too, can be calculated with the Standard Model. But if the quantum foam contains additional forces or particles that are not accounted for by the Standard Model, that would tweak the g-factor further.

• The first muon g−2 experiments began at CERN in 1959 at the initiative of Leon Lederman. A group of six physicists formed the first experiment, using the Synchrocyclotron at CERN. The first results were published in 1961,with a 2% precision with respect to the theoretical value, and then the second ones with this time a 0.4% precision, hence validating the quantum electrodynamics theory.
• A second experiment started in 1966 with a new group, working this time with the Proton-Synchrotron, still at CERN. Muon g−2 (pronounced "gee minus two") is a particle physics experiment at Fermilab to measure the anomalous magnetic dipole moment of a muon to a precision of 0.14 ppm,[1] which will be a sensitive test of the Standard Model. It might also provide evidence of the existence of entirely new particles.
• The muon, like its lighter sibling the electron, acts like a spinning magnet. The parameter known as the "g-factor" indicates how strong the magnet is and the rate of its gyration.

Where Muons wobble at faster rate?

The Muon g-2 experiment at a laboratory near Chicago involves sending the particles around a 14-metre ring and then applying a magnetic field. Under, the current laws of physics, encoded in the standard model, this should make the muons wobble at a certain rate. Instead, muons wobbled at a faster rate than expected. This might be caused by a force of nature that’s completely new to science. Muon g-2 experiment result shows a different force which doesn’t fall under the four categories of force i.e. gravity, electromagnetism, strong force and weak force. The muon is one of the sub-atomic particles which are considered building blocks of our world that are even smaller than the atom.

Who conducted the experiment?
The experiment, called Muon g–2 (g minus two), was conducted at the US Department of Energy’s Fermi National Accelerator Laboratory (Fermilab). It measured a quantity relating to the muon, following up a previous experiment at Brookhaven National Laboratory, under the US Department of Energy. Concluded in 2001, the Brookhaven experiment came up with results that did not identically match predictions by the Standard Model.
The Muon g–2 experiment measured this quantity with greater accuracy. It sought to find out whether the discrepancy would persist, or whether the new results would be closer to predictions. As it turned out, there was a discrepancy again, although smaller.

How this experiment is significant?

• The results from Brookhaven, and now Fermilab, hint at the existence of unknown interactions between the muon and the magnetic field — interactions that could involve new particles or forces. It is, however, not the last the word in opening up the road to new physics.
• To claim a discovery, scientists require results that diverge from the Standard Model by 5 standard deviations. The combined results from Fermilab and Brookhaven diverge by 4.2 standard deviations. While this may not be enough, it is very unlikely to be a fluke — that chance is about 1 in 40,000, the Argonne National Laboratory, also under the US Department of Energy, said in a press release.
• This is strong evidence that the muon is sensitive to something that is not in our best theory.