Subatomic particle
Most of the particles discovered are created by accelerating particles and colliding them against others, creating huge showers of new subatomic particles which decay extremely quickly. However, because the particles are moving close to the speed of light, the laws of special relativity become important and time dilation occurs. This means that time passes slower for the particle, and they can travel (and be measured) over a longer distance than non-relativity science would predict.