Coherent bremsstrahlung and a new possibility to monitor collisions of beams at colliders

We consider the coherent bremsstrahlung (CBS) at colliders with short bunches. CBS is radiation of particles of one bunch in the collective electromagnetic field of the oncoming bunch. It seems that CBS can be a potential tool for fast control over collisions and for measuring beam parameters. The bunch length σz can be found from the critical energy of the CBS spectrum Ec ∝ 1σz; the transverse bunch size σ⊥ is related to the photon rate dNγ ∝ 1σ⊥2. A specific dependence of dNγ on the impact parameter between the beams allows for a fast control over the beam displacement. We present the main characteristics of CBS calculated for B and φ factories, LHC (in the p-p and Pb-Pb modes), RHIC, VEPP-2M and VEPP-4M.