A particle in the Cerenkov effect. What particle?

Question

I've heard about Cerenkov radiation. Says When high velocity particles travel faster than the speed of light in a medium...I thought light was a wave(I understand light has properties of a wave and a particle so its convenient to think in terms of one or the other..but what is this particle they are speaking of? I assume they mean a Photon? So then, "when light travels faster than c" is that what they mean? And why dont they just say something to that effect then? Oh and light can be electromagnetically charged?

Ok so I understand its the speed of light in the medium and an almost massless particle can exceed that speed...I've also heard space is not a perfect vacuum..so wouldn't that also be a type of medium? See what I'm getting at?

Answer 1

No, they mean a charged particle like an electron.

Non-vacuum media slow down the apparent speed of light. A particle might be zipping through at faster than that speed (but less than c, the speed of light in a vacuum, which is the universal absolute speed limit).

So a charged particle will emit radiation, sort of like a sonic boom when an airplane travels through the air faster than the speed of sound.

A neutral particle like a neutrino does not couple to the E-M field, so it won't do this. (And of course, photons aren't charged either--they don't couple to themselves!)

But in a neutrino detector, the neutrino reacts with the water, which kicks out an electron, which does do this, and the radiation is picked up by light detectors.

edit: Space doesn't have enough matter present to create Cerenkov radiation--certainly not enough that you'd notice in any realistic situation. The speed of light in space is not measurably different than c.

Answer 2

Hi. Usually they are talking about neutrinos which, being nearly massless, can travel at or near c. When they interact with a medium like water they emit the radiation as they slow down.