Cherenkov radiation and pair production by particles traversing laser beams

It is shown that Cherenkov radiation can be observed at TESLA in electron collisions with optical laser pulses. The prospects for it to be observed at SLC, LEP, LHC and RHIC are discussed. The conclusions are compared with results for pair production. The problem of very high energy charged particles collisions with laser beams is widely discussed now, mostly in connection with the e + e −-pair production (see latest references [1, 2, 3, 4]) at SLC and TESLA X-ray laser facilities [5, 6, 7] and with some other issues of fundamental physics. Here, I would like to note that optical lasers can be used for studies of Cherenkov radiation. The results can be applied to measurements of beam energy, laser bunch parameters and, in general, to verify our ideas about the properties of the " photon medium ". X-ray lasers have been proposed for use in e + e −-pair production studies because the quanta energies are high enough to reach the threshold energy which in c.m.s. is equal to m + 2m e , where m e is the electron mass and m is the accelerated particle mass (equal to m e at SLC, LEP, TESLA, to the proton mass at LHC and to the nucleus mass at RHIC). At the same time, for studies of Cherenkov radiation another characteristics of a laser, namely its peak power density S, is important. It determines the index of refraction n of the " photon medium " in laser bunches. The difference of n from 1 is proportional to the density of photons in a laser pulse, i.e., to S. Just this difference defines the threshold of Cherenkov radiation, its emission angle and intensity 1. The parameter S is higher for optical lasers than for presently available X-ray lasers. That is why they would be preferred for Cherenkov radiation studies nowadays. Besides, the energy limitations also favour optical lasers for this purpose. The necessary conditions for Cherenkov radiation to be observed are the excess of the index of refraction n over 1, i.e. ∆n = n − 1 > 0 (1) and the real emission angle, given by the formula cos θ = 1 βn , (2) 1 The analogous problem was considered in Ref. [8] for particles traversing the cosmic microwave background radiation. The density of relic photons is, however, extremely low and, therefore, the index of refraction is so …