What: A ring-accelerator/collider for muons
Where: Undetermined (Fermilab has drawn up a purely speculative proposal for its site in Illinois)
Particles Smashed: Muons
Likelihood: Not likely in 2030s, maybe by mid-century
With masses between those of protons and electrons, muons are ideal for colliding--they are much heavier than electrons so they don’t radiate all their energy away, but not quite as heavy as protons. Protons are made of constituent particles, so when they collide not all of their energy is available to create new particles--some washes away in the dissolution of the proton itself into more elementary particles. Muons, on the other hand, are elementary. If we could smash them, nearly all of their energy would go toward creating new particles.
But muons are inherently unstable. Produce them in the lab, and they decay almost immediately. However, when you’re talking about accelerating things to velocities approaching the speed of light, relativity says you can cheat a little. Time dilation--the idea in relativity that tells us that the life cycle of a particle increases with its speed--means that if we could get muons moving fast enough before they begin decaying, they could live for much longer, at least long enough to make a few laps around an accelerator ring and smash into each other.
Muon colliders (the one pictured is a theoretical setup envisioned by Fermilab) are a cool idea that some physicists are putting a lot of thought into, Wyatt says, but they are unlikely to be the next big thing in particle physics. Like the 50-mile proton-proton ring, we’re just not at the point in the larger study of particle physics where we can--in good conscience--make a multi-billion commitment to smashing them. File under “inherently awesome, but unlikely before mid-century.”