Energy calibration at high-energy photon colliders

TL;DR

This paper discusses methods for calibrating the energy scale at high-energy photon colliders, emphasizing the use of the gamma-electron to eZ_0 process over Compton scattering due to nonlinear effects.

Contribution

It proposes that the gamma-electron to eZ_0 process is the most effective method for energy calibration at photon colliders, considering nonlinear effects in Compton scattering.

Findings

Compton scattering is less effective for calibration due to nonlinear effects.

The gamma-electron to eZ_0 process provides a reliable calibration method.

Calibration accuracy is crucial for Higgs and charged scalar mass measurements.

Abstract

Calibration of the absolute energy scale at high-energy photon (gamma-gamma, gamma-electron) 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 gamma-gamma to 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 m_e and laser photon energy \omega_0. However, this does not work at realistic photon colliders due to large nonlinear effects in Compton scattering at the conversion region (\xi^2 \sim 0.3). It is argued that the process gamma-electron to eZ_0 provides the best way to calibrate the energy scale of the detector, where the energy scale is given by m_Z.