Cherenkov detector
= Cherenkov detector
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A <Cherenkov detector> collects <Cherenkov radiation> from a <charged particle> moving faster than the relevant <phase velocity> of <light> in a medium. For a transparent medium of <refractive index> $n$ and particle speed $\beta c$, emission requires $\beta n>1$ and the cone angle satisfies $\cos\theta_C=1/(\beta n)$.
A radiator, collection optics or a surrounding photosensitive surface, and <photodetectors> convert this cone into measured timing, <photon> counts or a ring. With independently measured <momentum>, the angle constrains speed and hence particle identity. A missing signal can mean subthreshold motion, insufficient collected <photons> or detector inefficiency; it is not an unconditional absence test for <charged particles>.