Energy calibration at high-energy photon colliders

Abstract

Calibration of the absolute energy scale at high-energy photon (γγ, γe) colliders is discussed. The luminosity spectrum at photon colliders is broad and has a rather sharp high-energy edge, which can be used, for example, to measure the mass of the Higgs boson in the process γγ →H or masses of charged scalars by observing the cross-section threshold. In addition to the precise knowledge of the edge energy of the luminosity spectrum, it is even more important to have a way to calibrate the absolute energy scale of the detector. At first sight, Compton scattering itself provides a unique way to determine the beam energies and produce particles of known energies that could be used for detector calibration. The energy scale is given by the electron mass me and laser photon energy ω0. However, this does not work at realistic photon colliders due to large nonlinear effects in Compton scattering at the conversion region (ξ2 ∼ 0.3). It is argued that the process γe →eZ0 provides the best way to calibrate the energy scale of the detector, where the energy scale is given by mZ.