Scientists seek rare muon conversion that could signal new physics

Diana Kwon in Symmetry:

This weekend, members of the Mu2e collaboration dug their shovels into the ground of Fermilab's Muon Campus for the experiment that will search for the direct conversion of a muon into an electron in the hunt for new physics.

For decades, the Standard Model has stood as the best explanation of the subatomic world, describing the properties of the basic building blocks of matter and the forces that govern them. However, challenges remain, including that of unifying gravity with the other fundamental forces or explaining the matter-antimatter asymmetry that allows our universe to exist. Physicists have since developed new models, and detecting the direct conversion of a muon to an electron would provide evidence for many of these alternative theories.

“There's a real possibility that we'll see a signal because so many theories beyond the Standard Model naturally allow muon-to-electron conversion,” said Jim Miller, a co-spokesperson for Mu2e. “It'll also be exciting if we don't see anything, since it will greatly constrain the parameters of these models.”

Muons and electrons are two different flavors in the charged-lepton family. Muons are 200 times more massive than electrons and decay quickly into lighter particles, while electrons are stable and live forever. Most of the time, a muon decays into an electron and two neutrinos, but physicists have reason to believe that once in a blue moon, muons will convert directly into an electron without releasing any neutrinos. This is physics beyond the Standard Model.

Under the Standard Model, the muon-to-electron direct conversion happens too rarely to ever observe. In more sophisticated models, however, this occurs just frequently enough for an extremely sensitive machine to detect.

The Mu2e detector, when complete, will be the instrument to do this.

More here. [Thanks to Farrukh Azfar.]