I have read this:




We know that neutrinos travel in vacuum very close to the speed of light (0.99c).

Neutrinos do have rest mass.

We know that in a thick medium, like glass, light travels slower then c (2/3c).

Neutrinos interact very weakly with matter, so their speed in glass would not really slow down.

We know that particles in a thick medium that travel faster then light, (they hit an electron and that will emit) emit Cherenkov radiation.

It would be possible for neutrinos to travel faster then light in glass. Light speed in glass is 2/3c which is slower then 0.99c.


  1. When neutrinos travel through glass, do they emit Cherenkov radiation? Why can't they themselves emit the Cherenkov, why can only electrons do it? Is there a QM explanation for charge to be a prerequisite for this?

2 Answers 2


Only charged particles emit Cherenkov radiation. However, a neutrino can interact with a atom of the glass in a way that produces a high-energy electron, which itself is traveling faster than the speed of light through glass. That electron will produce Cherenkov radiation. This is how the Super-Kamiokande neutrino detector in Japan works, only with water instead of glass.

There is also Askaryan radiation, where ultra-high-energy neutrinos generate a cascade of secondary particles with an overall charge that produces coherent radio radiation. This is how scientists use the Moon (LUNASKA) and Antarctica (ANITA) as neutrino detectors.

To answer your added question (why only charged particles can emit Cherenkov radiation), a particle must be able to interact with the electromagnetic force in order to release electromagnetic radiation. Electric charge is exactly the property that allows a particle to have this interaction, much in the same way that mass couples to gravity, and color charge couples to the strong force. Without electric charge, the electromagnetic force can't touch a particle.

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    $\begingroup$ One of the arguments against superluminal neutrinos was that they would emit analogs of Cherekov radiation, as described here (arxiv.org/abs/1109.6562). I do not see any obvious reason that these processes would not also be possible for neutrinos in a medium- do you? However, they might be slow enough processes to not be relevant for the short time a neutrino is in a detector. $\endgroup$
    – Rococo
    Jun 12, 2018 at 1:54

We know that particles in a thick medium that travel faster then light, emit Cherenkov radiation.

That's not quite correct. It is only charged particles that do so. Neutrinos are uncharged.

Neutrino detectors that use this method are imaging the (charged) decay products from a neutrino interaction. So without an interaction, there is no visible radiation.

As far as I'm aware, you would get similar radiation in glass as other materials, it's just that glass is not as useful. To get a nice instrument, you want a large volume to increase the interaction rate. But glass is really annoying to cast in large volumes. It shrinks and will crack easily. So you'd either need to have a small instrument, or you'd have to use multiple pieces, which causes reflections at the boundaries. Other materials don't have these drawbacks.


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