A proton meets an antiproton. What happens to the pair?
The LHC's builders spent years, and billions of dollars, raising its collision energy higher and higher. If the goal is just to smash protons together, any speed would smash them. Why pay so much for energy?
You have already seen annihilation: a particle meets its antiparticle, and the pair's mass turns into energy. That conversion runs both ways, because mass can convert into energy and energy can convert into the mass of new particles.
A low-energy collision can make only light particles. A heavier particle simply cannot appear: there is not enough energy to become its mass.
That is why physicists run collisions at the greatest energies they can reach: each rise in energy brings particles into reach that no earlier machine could make. The Higgs boson is the famous case. Physicists found the Higgs boson only once the LHC's collisions reached a large enough energy. A later topic puts an exact number on the energy-to-mass trade.
Why did finding the Higgs boson have to wait for the LHC's record collision energies?
A new particle's mass comes from the collision's energy, because mass can convert into energy and energy can convert into the mass of new particles.
The Higgs boson is a heavy particle, so making one takes a large amount of energy.
Collisions below that energy could never supply the Higgs boson's mass; the LHC's collisions could.
An accelerator is upgraded so its collisions carry more energy. What changes about the particles it can create?
Energy can convert into the mass of new particles.
More collision energy can become more mass.
The upgraded collisions can create heavier particles than the old ones could.
Why do physicists run particle collisions at the greatest energies they can reach?
A collider's collisions carry only a small amount of energy. Which new particles can they create?
A brand-new particle appears in a collision. Where does its mass come from?
A future collider is designed to hunt a particle predicted to be far more massive than any particle yet made. What must the new machine deliver?
In one collision, two light particles appear. In another collision at far higher energy, a much heavier particle appears. What explains the difference?
A collider runs for years at one fixed energy and only ever produces the same familiar set of particles. A predicted heavier particle never appears. Why?