The Muon Collider: “Deep Thought” Beyond the LHC?

Neutrino_event Some scientists are already looking beyond the Large Hadron Collider and onto the next generation of ultimega-atom-smasher.  That's because scientists actually plan things and can concentrate for longer than four seconds, unlike the mass media which reports on them.  One potential particle pulverising system is a muon collider: the latest concept in the cutting edge that parts particles.

It might seems spoiled to be calling for another multimillion dollar megacollider when the latest one hasn't even started, but the LHC is no Deep Thought: they aren't going to turn it on and have the answer to Life, the Universe and Everything (eventually) tumble out.  Whatever the results of the proton-pounding experiments underneath the Franco-Swiss border there are whole swathes of the high-energy particle spectrum still out of reach – and which we want to look at next will be determined by the LHC.


The muon collider concept combines exciting potential with challenging problems.  Muons are only a ninth of the mass of protons and so can be accelerated to higher energies with current hardware (in fact, because they're made of fewer subatomic bits they can reach higher effective energies even with less powerful equipment).  They're two hundred times heavier than electrons, but because they're less prone to radiate away energy via synchrotron radiation when being bent around curves by magnetic fields, they can be kept in rings at energy levels where electrons would require vast linear accelerators.

The challenges are just as cool: a muon's stable lifetime is only two point two microseconds, and when faced with the problem "they only hang around for a couple millionths of a second" the designers said "let's just accelerate them to close to the speed of light" – that way they hang around long enough (in our frame) due to relativistic time dilation.  If that sounds improbable, it's already happened to you a bunch of times while reading this sentence: muons created by cosmic ray impacts classically couldn't survive long enough to reach the surface, it's only time dilation extending their life from our reference frame that lets them stream into the surface of the Earth, bubble chambers, and your body right now.

There are still extraordinarily significant challenges to overcome: how do you streams muons into the accelerator from the reactions that cause them, who wants to pay for something this big, and will they be able to overcome other accelerator strategies to get that funding?  Only time, and awesome science, will tell.

Luke McKinney via nature.com

Image: Underground neutrino experiments have established that neutrinos oscillate among various “flavors” (electron neutrino, muon neutrino, and tau neutrino) and therefore must have at least a tiny mass, different for each flavor. (Image copyright Kamioka Observatory, Institute for Cosmic Ray Research, The University of Tokyo)

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