Table 2 Summary of the uncertainties and their impacts on the measured branching fraction \({\mathcal{B}}(Z\to \ell \tau)\)

Source of uncertainty	Uncertainty on \({\mathcal{B}}(Z\to \ell \tau \ )\) (×10⁻⁶)
	eτ	μτ
Statistical	±3.5	±2.8
Systematic	±2.3	±1.6
τ leptons	±1.9	±1.5
Energy calibration	±1.3	±1.4
Jet rejection	±0.3	±0.3
Electron rejection	±1.3
Light leptons	±0.4	±0.1
\({E}_{\,\text{T}}^{\text{miss}\,}\), jets and flavour tagging	±0.6	±0.5
Z-boson modelling	±0.7	±0.3
Luminosity and other minor backgrounds	±0.8	±0.3
Total	±4.1	±3.2

The statistical uncertainties include those in the determination of the yields of the events with fakes and from Z → ττ or Z → ℓτ decays. The uncertainties related to light leptons include those in the trigger, reconstruction, identification and isolation efficiencies, as well as energy calibrations. The uncertainties related to jets and \({E}_{\,\text{T}}^{\text{miss}\,}\) include those in energy calibration and resolution. The uncertainties related to the Z-boson modelling include those in the correction of the simulated transverse momentum and the measured production cross-section of the Z boson.

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