# Fermilab

## Inquiring Minds

What is the exact speed a particle can be accelerated?

We usually express the particle velocity as a fraction of the velocity of light. The formula is:

v/c = Sqrt(E^2-m^2*c^4)/E.

where E is the particle energy in GeV and m is the particle mass. Particles with 0 mass always travel at the speed of light regardless of their energy. The only particle that we know to be massless is the photon, the basic unit (particle) of light. Neutrinos have a very small mass, but may not be massless. The neutrino mass is a subject of intense research at Fermilab and other laboratories.

In high energy accelerators, particles travel at nearly the speed of light, but they never exceed the speed of light. For example, the Tevatron accelerates both protons and antiprotons to 980 GeV. The mass of the proton and antiproton are the same and equal to 0.93827 GeV/c^2.

>From the formula quoted above, you can calculate that the speed of particles in the Tevatron is equal to 99.999954% of the speed of light.

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