Cosmic Rays Are More Energetic Than LHC Particles, And This Faster-Than-Light Trick Reveals Them
“The other option would be to catch these cosmic ray particles before they ever reached the Earth; you’d need to go to space to see them. But even if you did that, you’d be limited by the sensitivity of your detector and the amount of energy that could be directly deposited within it. Going to space also comes with a tremendous launch cost; the Fermi gamma ray telescope, which detects individual high-energy photons rather than cosmic rays directly, cost approximately $690 million, more than twice the projected cost of the entire Čerenkov Telescope Array.
Instead, by catching the particles and photons that result from a cosmic ray striking the atmosphere in over 100 locations across the globe, we can come to understand the origin and properties of these ultra-relativistic particles, as well as the astrophysical sources that create them. All of this is possible because we understand the physics of particles moving faster-than-light in one special medium: Earth’s atmosphere. Einstein’s laws might be unbreakable, but the trick of slowing light down enables us to detect something very cleverly that we wouldn’t be able to measure otherwise!”
If you want to measure a high-energy particle, you build an enormous detector. You do this because you want the particle and its decay products (or secondary particles) to deposit their energy in the detector, so you can reconstruct their position, momenta, charge, and other properties that will enable you to understand where they came from. But the Universe gives us particles that are far too high in energy for that to be a workable solution. So what do we do, as physicists?
We use all the tricks nature makes available to us, including slowing light down to leverage the phenemenon of Cherenkov radiation! Here’s how we’re reconstructing cosmic rays from the ground with this special type of light.