Measurement of the effective leptonic weak mixing angle

TL;DR

This paper reports a precise measurement of the effective leptonic weak mixing angle using proton-proton collision data from the LHCb experiment, providing important tests of the Standard Model and electroweak theory.

Contribution

First measurement of the effective leptonic weak mixing angle at 13 TeV using forward-backward asymmetry in dimuon production at LHCb.

Findings

Measured value of sin^2θ_eff^l = 0.23147 ± 0.00044 ± 0.00005 ± 0.00023

Results are consistent with previous measurements and global electroweak fits

Analysis used data from 2016-2018 with 5.4 fb^{-1} luminosity

Abstract

Using $pp$ collision data at $\sqrt{s}=13$ TeV, recorded by the LHCb experiment between 2016 and 2018 and corresponding to an integrated luminosity of $5.4$ fb$^{-1}$, the forward-backward asymmetry in the $pp \to Z/\gamma^{*} \to \mu^+\mu^-$ process is measured. The measurement is carried out in ten intervals of the difference between the muon pseudorapidities, within a fiducial 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 effective leptonic weak mixing angle is $\sin^2\theta_{\rm eff}^\ell = 0.23147 \pm 0.00044 \pm 0.00005 \pm 0.00023$, where the first uncertainty is statistical, the second arises from systematic uncertainties associated with the asymmetry measurement, and the third arises from uncertainties in the fit model used to extract $\sin^2\theta_{\rm eff}^\ell$ 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 fit.