Ordinary and coherent bremsstrahlung at linac-ring ep colliders

Authors: V.G. SERBO, D.V. SEREBRYAKOVA

Abstract: The ordinary bremsstrahlung $ep \rightarrow ep\gamma$ can be used at the linac-ring $ep$ colliders for luminosity measurement. It is known that at high energies this process has a large correction due to beam-size effect. We have calculated this effect for $ep$ colliders of the linac-ring type. For the LHC+CLIC collider the correction exceeds 10\% for $E_{\gamma} < 0.95\;E_e$. As a rule, the bremsstrahlung of protons in the $ep$ scattering is not considered due to its small cross section. However, if the photon energy $E_{\gamma}$ becomes small enough, the number of produced photons become large because in this case the radiation is determined by the interaction of a proton with the collective electromagnetic field of the electron bunch. It is coherent bremsstrahlung (CBS). We present the main characteristics of CBS calculated for linac-ring $ep$ colliders. At the LHC+CLIC collider it should be about $1700 \; dE_\gamma /E_\gamma$ photons for a single collision of bunches at $E_\gamma \stackrel{<}{\sim} 0.2$ MeV. It seems that CBS can be a potential tool for fast control over collisions and for measuring beam parameters. Indeed, the electron bunch length $l_e$ can be found from the critical energy $E_c \propto 1/l_e$, the transverse bunch size $\sigma_{\perp}$ is related to the photon rate $dN_{\gamma} \propto 1/\sigma_{\perp}^2$. A specific dependence of $dN_{\gamma}$ on the impact parameters between the beams allows for a fast control over beam displacement.

Keywords:

Full Text: PDF