Muon g–2: challenge to particle physics

Context

The newly published results of an international experiment show the possibility of new physics which would govern the laws of nature.

Key-highlights of the Study

• A subatomic particle called the muon were studied.
  • The results show that the particles do not match the predictions of the Standard Model.
• Experiment:The experiment which is called Muon g–2 (g minus two) was conducted at the US Department of Energy’s Fermi National Accelerator Laboratory (Fermilab).
  • The quantity which was measured is called the g–factor which is a measure that derives from the magnetic properties of the muon.
  • Muons act as a tiny internal magnet.
  • In a strong magnetic field, the direction of this magnet “wobbles” 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.

How does it work?

• In the g–2 experiment, scientists measure it with high-precision instruments.
• They generate muons and got them to circulate in a large magnet.
• The muons interact with a “quantum foam” of subatomic particles “popping in and out of existence”.
• These interactions affect the value of the g-factor, causing the muons to wobble slightly faster or slightly slower.
• 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 and a different result is observed from the standard results.
  • By calculating the deviation which is called anomalous magnetic moment the results are observed.

What were the findings?

• The results, while diverging from the Standard Model prediction.
• The results hint at the existence of unknown interactions between the muon and the magnetic field.
• This interactioncould involve new particles or forces.