Precise test of lepton flavour universality in $W$-boson decays into muons and electrons in $pp$ collisions at $\sqrt{s}=13$ TeV with the ATLAS detector

Abstract

The ratio of branching ratios of the $W$ boson to muons and electrons, $R_W^{\mu /e}=B(W\to \mu \nu )/B(W\to e\nu )$, has been measured using 140 fb${}^{-1}$ of $pp$ collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector at the LHC, probing the universality of lepton couplings. The ratio is obtained from measurements of the $t\bar{t}$ production cross-section in the $ee$, $e\mu$ and $\mu \mu$ dilepton final states. To reduce systematic uncertainties, it is normalised by the square root of the corresponding ratio $R_Z^{\mu \mu /ee}$ for the $Z$ boson measured in inclusive $Z\to ee$ and $Z\to \mu \mu$ events. By using the precise value of $R_Z^{\mu \mu /ee}$ determined from $e^{+}{e}^{-}$ colliders, the ratio $R_W^{\mu /e}$ is determined to be $R_W^{\mu /e}=0.9995\pm 0.0022\pm 0.0036\pm 0.0014$. The three uncertainties correspond to data statistics, experimental systematics and the external measurement of $R_Z^{\mu \mu /ee}$, giving a total uncertainty of 0.0045, and confirming the Standard Model assumption of lepton flavour universality in $W$-boson decays at the 0.5% level.

46 pages in total, author list starting page 29, 6 figures, 5 tables, published in EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/TOPQ-2023-28/

References in corpus (26)

• The automated computation of tree-level and next-to-leading order differential cross sections, and their matching to parton shower simulations
• Matching NLO QCD computations with Parton Shower simulations: the POWHEG method
• New parton distributions for collider physics
• Herwig++ Physics and Manual
• A parton shower algorithm based on Catani-Seymour dipole factorisation
• Single-top Wt-channel production matched with parton showers using the POWHEG method
• FEWZ 2.0: A code for hadronic Z production at next-to-next-to-leading order
• NLO vector-boson production matched with shower in POWHEG
• Measurement of the $Z/{\gamma }^{\ast }$ boson transverse momentum distribution in $pp$ collisions at $\sqrt{s}$ = 7 TeV with the ATLAS detector
• Muon reconstruction and identification efficiency in ATLAS using the full Run 2 $pp$ collision data set at $\sqrt{s}=13$ TeV
• Measurement of the $\tau$ lepton polarization and $R(D^{\ast })$ in the decay $\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau }$ with one-prong hadronic $\tau$ decays at Belle
• Luminosity determination in $pp$ collisions at $\sqrt{s}=13$ TeV using the ATLAS detector at the LHC
• ATLAS flavour-tagging algorithms for the LHC Run 2 $pp$ collision dataset
• Test of lepton universality in $b\to s{\ell }^{+}{\ell }^{-}$ decays
• Measurement of the $c$-jet mistagging efficiency in $t\bar{t}$ events using $pp$ collision data at $\sqrt{s}=13$ TeV collected with the ATLAS detector
• Calibration of the light-flavour jet mistagging efficiency of the $b$-tagging algorithms with $Z$+jets events using 139 ${\mathrm{fb}}^{-1}$ of ATLAS proton-proton collision data at $\sqrt{s}=13$ TeV
• Measurement of the ratios of branching fractions $\mathcal{R}(D^{\ast })$ and $\mathcal{R}(D^0)$
• Test of lepton flavour universality using $B^0\to D^{\ast -}{\tau }^{+}{\nu }_{\tau }$ decays with hadronic $\tau$ channels
• Higher-order corrections for $tW$ production at high-energy hadron colliders
• Measurements of top-quark pair differential cross-sections in the lepton+jets channel in $pp$ collisions at $\sqrt{s}$=13 TeV using the ATLAS detector
• Studies of the muon momentum calibration and performance of the ATLAS detector with $pp$ collisions at $\sqrt{s}$=13 TeV
• Measurement of forward $W\to e\nu$ production in $pp$ collisions at $\sqrt{s}=8$TeV
• Inclusive and differential cross-sections for dilepton $t\bar{t}$ production measured in $\sqrt{s}=13$TeV $pp$ collisions with the ATLAS detector
• Electron and photon efficiencies in LHC Run 2 with the ATLAS experiment
• Precision measurement of the W boson decay branching fractions in proton-proton collisions at $\sqrt{s}=$ 13 TeV
• Measurement of the $t\bar{t}$ production cross-section in $pp$ collisions at $\sqrt{s}=5.02$ TeV with the ATLAS detector

Cited by in corpus (2)

• Climbing to the Top of the ATLAS 13 TeV data
• Probes of flavour symmetry and violation with top quarks in ATLAS and CMS