Faster particles, accelerating costs
The collision energy in a proton collider must be substantially higher than might otherwise be the case because the energy is parceled out to varying degrees among all the quarks and gluons in the mix, not just among two protons.
Researchers at the European Organization for Nuclear Research (CERN) are laying plans to upgrade the LHC’s power in about 10 years. Still, scientists say they are fast approaching the limits for affordable proton colliders, even when an international collaboration is sharing the cost. At some point on the climb up the collision-energy ladder, the protons’ heft won’t prevent them from losing increasing amounts of travel energy as they constantly shift directions in a circular ring, rendering them less practical. And the magnetic fields needed to keep a rein on the protons would grow so high that no known, or at least affordable, material could withstand the physical stresses the magnetic fields would set up.
This has prompted many physicists looking harder at electrons, and their heavier cousins, muons, to literally get more bang for the buck. Electrons have been getting a workout for years at the Stanford Linear Accelerator Center (SLAC) in Menlo Park, Calif., and at the LHC’s predecessor at CERN, the Large Electron-Positron Collider.
Unlike protons, electrons are fundamental particles – they have no internal components. So every hit is clean; all of the energy of the collision goes into forming the heavier particles scientists are interested in. Scientists can accomplish the same physics with fewer collisions than a proton collider requires.