The Z total decay width ΓZ can be measured at FCC-ee with sample of 3.5 × 1012 Z → hadrons events produced around the Z pole at √s ≈ 87.8, 91.2, and 93.9 GeV, with a statistical precision of 4 keV [1]. Experience from LEP showed that a limiting systematic uncertainty comes from the uncorrelated point-to-point error on the centre-of-mass energies of the three resonance scan points. At FCC-ee, this error can possibly be controlled in situ with the invariant mass distributions obtained from large dimuon event samples [1]. The requirements of the detector design (muon momentum and angular resolution and scale stability) to match the statistical precision will be studied in the context of the constraints from the full interaction region layout (beam crossing angle, beam energy spread, magnetic field). As a by-product, the possible improvements brought about by a five-point scan of the Z resonance will be investigated.
Emilia Leogrande [email protected]
E. Leogrande, E. Perez, P. Janot,...
-Point-to-point uncertainty on sqrt(s) with dimuons and momentum scale stability E. Leogrande, talk at the Physics Performance meeting, Dec 14, 2020