https://doi.org/10.1140/epjp/s13360-021-01894-y
Review
The 
challenges at FCC-ee
Niels Bohr Institute, Copenhagen University, Copenhagen, Denmark
Received:
5
May
2021
Accepted:
30
July
2021
Published online:
22
September
2021
At FCC-ee, about 
events will be produced. This high statistics in the clean 
environment opens the possibility of much improved determinations of -lepton properties and, via the measurement of the polarisation, of the neutral-current couplings of electrons and 
s. Improved measurements of -lepton properties—lifetime, leptonic branching fractions, and mass—allow important tests of lepton universality. The experimental challenge is to match as far as possible statistical uncertainties generally at the 
level. This applies in particular to the lifetime measurement, which is derived from the 2.2-mm average flight distance, and for the branching fraction and polarisation measurements, where the cross-channel contamination is of particular concern. These issues raise strict detector requirements, in particular, on the accuracy of the construction and alignment of the vertex detector and of the precise calorimetric separation and measurement of photons and 
s in the collimated decay topologies.
The original online version of this article was revised to add additional funding information.
A correction to this article is available online at https://doi.org/10.1140/epjp/s13360-022-02959-2.
Copyright comment corrected publication 2022
© The Author(s) 2021. corrected publication 2022
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