Collision-energy calibration and monochromatisation studies at FCC-ee

The Future Circular Collider (FCC) technical and financial Feasibility Study (FS) includes a work
package on Energy Calibration, Polarisation and Monochromatisation (EPOL), which is concerned
with the precision determination of the centre-of-mass energy at the e+e− machine, FCC-ee. To
achieve this goal it is proposed to use resonant depolarisation and possibly spin precession meas-
urements, in conjunction with precise measurement by the detectors of the energy spread and other
parameters with physics events. Beam diagnostics, provided by polarimeters and beam-position
monitors, play an essential role in monitoring the polarisation level and controlling numerous beam
parameters at the interaction point. Specific items of accelerator equipment include polarisation
wigglers and depolarising RF-kickers. The target is to achieve a precision commensurate to the
remarkable statistical precision achievable in the physics experiments. The possible monochromat-
isation of colliding beams in view of a measurement of the e+e− → H(125) process is also being
studied, with the specific requirements of this procedure under investigation. A review is presented
of the status of these activities at the end of the FS, together with the outlook for future work.