Abstract
The FCC-ee offers powerful opportunities for direct or indirect evidence for physics beyond the standard model, via a combination of high-precision measurements and searches for forbidden and rare processes and feebly coupled particles. A key element of FCC-ee physics program is the measurement of the Z lineshape from a total of 5times 10^{12} Z bosons and a beam-energy calibration with relative uncertainty of 10^{-6}. With this exceptionally large event sample, five orders of magnitude larger than that accumulated during the whole LEP1 operation at the Z pole, the defining parameters—m_mathrm{Z}, Gamma _mathrm{Z}, N_nu , sin ^2theta _mathrm{W}^mathrm{eff}, alpha _mathrm{S}(m_mathrm{Z}^2), and alpha _mathrm{QED}(m^2_mathrm{Z})—can be extracted with a leap in accuracy of up to two orders of magnitude with respect to the current state of the art. The ultimate goal that experimental and theory systematic errors match the statistical accuracy (4 keV on the Z mass and width, 3times 10^{-6} on sin ^2theta _mathrm{W}^mathrm{eff}, a relative 3times 10^{-5} on alpha _mathrm{QED}, and less than 0.0001 on alpha _mathrm{S}) leads to highly demanding requirements on collider operation, beam instrumentation, detector design, computing facilities, theoretical calculations, and Monte Carlo event generators. Such precise measurements also call for innovative analysis methods, which require a joint effort and understanding between theorists, experimenters, and accelerator teams.
Highlights
With an integrated luminosity of 150 ab−1 collected in ≈ 4 years of running at centre-ofmass energies between 88 and 94 GeV, FCC-ee [1] offers a unique opportunity to perform ultra-precise electroweak measurements of the Z resonance
New theoretical paths will have to be pursued in order to provide most precise predictions for experimental observables [4], and detailed experimental studies will have to be performed to optimise accelerator and detector designs
In the following we focus on some elements of the challenge that we consider relevant for success
Summary
With an integrated luminosity of 150 ab−1 collected in ≈ 4 years of running at centre-ofmass energies between 88 and 94 GeV, FCC-ee [1] offers a unique opportunity to perform ultra-precise electroweak measurements of the Z resonance. Robust procedures to monitor other relevant beam collision parameters and the relative uncertainties between the energy points in Z lineshape scans [3] are an integral part of the physics program. New theoretical paths will have to be pursued in order to provide most precise predictions for experimental observables [4], and detailed experimental studies will have to be performed to optimise accelerator and detector designs. Exploring new analysis strategies and observables to simultaneously reduce both theoretical and experimental uncertainties will be another essential component of the challenge. Separate access to the left- and right-handed components of the couplings will be available at FCC-ee even in the absence of polarised beams [8], as described below
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