The speed of light in a vacuum is known to be around 299,792,458 m/s. This is in theory as fast as light can go – not any faster. Unlike light, particles themselves have mass, so according to Einstein’s theory, they themselves cannot reach the speed of light even if you increase energy input as they become more massive. Then we would have to take into account machine losses due to vacuum pressure, secondary yields, other electromagnetic forces as such that would have an effect on particles.
For reference, the Fermi National Accelerator Laboratory (Fermilab) = 99.997% (a few sources state this)
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