Alex Keshavarzi interview: How muons could reveal exotic new physics

Precision measurements have long suggested that particles called muons, closely related to the electron, are misbehaving. Now, it seems their shenanigans might be pointing to the presence of new particles


9 February 2022

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Jennie Edwards

FOR decades, physicists have been aware of a gnawing anomaly in the behaviour of a mysterious fundamental particle, the muon. Muons are the heavier cousins of the electrons that run though power lines and bring our devices to life. But when we study muons’ properties in granular detail, the results differ ever so slightly from predictions. Far from being a worry, this anomaly is cause for major excitement.

The so-called standard model – a list of the fundamental particles, their properties and associated forces – works incredibly well, as far as it goes. The trouble is that most physicists believe it paints an incomplete picture. There must be other particles and forces out there, but despite our best efforts, we haven’t been able to unmask them.

The muon anomaly could be a window to this hidden world. Its prediction-defying behaviour is thought to be a sign that it is interacting with some undiscovered particle. But because the measurements of the muon are so incredibly subtle, it has long been frustratingly unclear whether the anomaly is real – it could be a statistical fluke that will fade away on closer inspection.

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At Fermilab, near Chicago, muons zip around a ring in a search for new physics

Reidar Hahn/Fermilab

Soon, we should find out. Using a ring of magnets the size of a house, the Muon g-2 experiment at the Fermi National Accelerator Laboratory (Fermilab) near Chicago, Illinois, is probing their properties like never before. Alex Keshavarzi is on the experimentalteam of Muon g-2, based at the University of Manchester, UK. He told New Scientist about the …