This first Mu2e blog is designed to serve as an introduction to the purpose of the experiment. Stay tuned to Quantum Diaries for future Mu2e posts regarding some of the more subtle aspects of this unique experiment.
The layout of the Mu2e experiment. Muons are produced from a proton beam hitting a target and captured using magnetic fields. They are then transferred down the s-shaped transfer line to the stopping target . Stopped muons will decay, and the resulting electron will be studied using the particle detectors. Credit: symmetry magazine/Sandbox Studio
When the muon — a heavy version of the electron — was discovered, Isidor Rabi famously asked, “Who ordered that?”
Well, the Mu2e experiment at Fermilab would now like to place its order for 1020, or 100 trillion, of these interesting particles. To put this staggering number in context, the Mu2e experiment needs almost as many muons as there are grains of sand on Earth.
Since the time of its discovery, scientists have questioned why the muon wouldn’t decay directly into an electron and a photon. It seems like a natural decay if the muon is just a heavy version of the electron. However, this decay has never been observed.
Similar to the decay, it may be possible for a muon to convert directly into an electron in the presence of a nucleus (the nucleus is required to conserve momentum and energy). Experimental limits suggest that if this occurs at all, it must occur for less than one out of 10 13 , or 10 billion, muons. The Mu2e experiment needs so many muons because it plans to improve on the sensitivity of previous experiments to this so called muon-to-electron conversion by four orders of magnitude. That is, the goal of the first two-year run of the experiment is to be sensitive to this process even if only one muon out of 10 17 , or 100 billiard. converts into an electron in this way. A plan for future experimental runs may even improve this by two more orders of magnitude.
Can’t wait for the next blog? Then check out these sites for more information:
- Mu2e experiment website
- Recent Mu2e article in symmetry magazine
- Fact sheet on Mu2e
— Craig Group
