Image Credit: CERN.

Temperature is a macroscopic quantity. It is meant that temperature is a property of a collection of particles.

 
We can only talk about the temperature of atoms that make up an object. The temperature that we measure is caused by the random motions of atoms in an object. Thereby, we can’t speak about the temperature of a particle. However, It will be interesting if we are able to increase the random motion of atoms to relativistic speeds. What would happen?