Measurement of the efective leptonic weak mixing angle

Abstract

Using pp collision data at √ s = 13 TeV, recorded by the LHCb experiment between 2016 and 2018 and corresponding to an integrated luminosity of 5.4 fb−1 , the forwardbackward asymmetry in the pp → Z/γ∗ → µ +µ − process is measured. The measurement is carried out in ten intervals of the diference between the muon pseudorapidities, within a fducial region covering dimuon masses between 66 and 116 GeV, muon pseudorapidities between 2.0 and 4.5 and muon transverse momenta above 20 GeV. These forward-backward asymmetries are compared with predictions, at next-to-leading order in the strong and electroweak couplings. The measured efective leptonic weak mixing angle is sin2 θ ℓ ef = 0.23147 ± 0.00044 ± 0.00005 ± 0.00023, where the frst uncertainty is statistical, the second arises from systematic uncertainties associated with the asymmetry measurement, and the third arises from uncertainties in the ft model used to extract sin2 θ ℓ ef from the asymmetry measurement. This result is based on an arithmetic average of results using the CT18, MSHT20, and NNPDF31 parameterisations of the proton internal structure, and is consistent with previous measurements and with predictions from the global electroweak ft.