Precise test of lepton flavour universality in W-boson decays into muons and electrons in pp collisions at √(s)=13 TeV with the ATLAS detector
arxiv(2024)
摘要
The ratio of branching ratios of the W boson to muons and electrons,
R^μ/e_W=B(W→μν)/B(W→ eν), has been measured
using 140 fb^-1 of pp collision data at √(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 tt̅ production
cross-section in the ee, eμ and μμ dilepton final states. To reduce
systematic uncertainties, it is normalised by the square root of the
corresponding ratio R^μμ/ee_Z for the Z boson measured in inclusive
Z→ ee and Z→μμ events. By using the precise value
of R^μμ/ee_Z determined from e^+e^- colliders, the ratio
R^μ/e_W is determined to be R^μ/e_W = 0.9995 ± 0.0022 ± 0.0036
± 0.0014. The three uncertainties correspond to data statistics,
experimental systematics and the external measurement of R^μμ/ee_Z,
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.
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