Muon

Meet The Muon, The Electron’s Short-Lived Big Brother

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You’ve heard of electrons—they’re the negatively charged subatomic particles that swarm about the nucleus of every atom. But if you take an electron, blow it up to more than 200 times its mass and make it blink out of existence faster than a bullet can leave a gun, you’ve got a muon (pronounced not like a cow but like a kitten: myoo-on). Why is such a heavy, short-lived particle important? Scientists aren’t sure, but they have some fascinating hunches.

 

The Second Elementary Particle

 By World War I, scientists knew all matter was made up of atoms, which in turn were made up of a nucleus of protons and neutrons surrounded by electrons. By the 1930s, scientists believed those particles, plus photons, neutrinos, and the antimatter version of electrons known as positrons, were the whole of the fundamental particles that made up the universe. But there was a problem. (Isn’t there always?).

Scientists who studied cosmic rays—the showers of high-energy particles that rain down on our atmosphere from exploding stars and black holes—couldn’t explain what they were made of with the particles they had. Instead of interacting with the lead blocks the way the known particles would, some of the particles just passed right through. Finally, a Caltech physicist named Carl Anderson was able to use the same methods he had used for his Nobel Prize-winning discovery of antimatter to come to the truth: the penetrating particles were a different type of particle altogether, one that was like an electron but heavier. That made it the second elementary particle (a particle that can’t be broken down any further) ever discovered. After some time being called a “mesotron,” this new particle was named the muon. Still, what the heck was it? Nobel laureate Isidor Isaac Rabi echoed many people’s sentiments when he said of the muon’s discovery, “Who ordered that?”

Elementary particles in the Standard Model

The Modern-Day Muon

 Today, there are 16 elementary particles in the Standard Model of Physics, and the muon is just one of them (you can check out the others in the diagram above). We know a lot more about it today—its hefty mass to eight decimal places, its ridiculously short half-life to the picosecond—but there’s still a bit of Rabi’s opinion in our knowledge of the muon. Still, scientists are hopeful. “The muon will have the last laugh,” professor Mark Lancaster told Symmetry Magazine. “There’s still a lot we don’t know about fundamental interactions and the subatomic world, and we think that the muon might have the answers.”

It might seem difficult to study a particle that decays millions of times faster than the blink of an eye, but physicists have a trick up their sleeve: particle accelerators. When you accelerate something close to the speed of light, it lives longer than it would otherwise (thanks to Einstein’s special theory of relativity). Studying them opens up a world of possible answers to important questions: Why are there so many particles? Are there more subatomic forces we don’t know about? We don’t know if muons are the keys to these mysteries, but like we said: scientists have a hunch.

Watch And Learn: Our Favorite Videos About Particle Physics

The Standard Model Of Particle Physics

Confused about the elementary particles? This video has got your back.