Precise test of lepton flavour universality in W-boson decays into muons and electrons in pp collisions at √s=13\,Te-1.00006ptV with the ATLAS detector

This is the authors' abstract. We don't add key points for this paper.

The ratio of branching ratios of the W boson to muons and electrons, R\,μ /eW=B(W→ μ ν ) R W μ / e = B ( W → μ ν ) / B(W→ eν ) B ( W → e ν ) , has been measured using 140\, fb⁻¹\, 140 fb - 1 of pp collision data at √s=13 s = 13 Te-1.00006ptV Te V collected with the ATLAS detector at the LHC, probing the universality of lepton couplings. The ratio is obtained from measurements of the tt̄ t t ¯ production cross-section in the ee , eμ e μ and μ μ μ μ dilepton final states. To reduce systematic uncertainties, it is normalised by the square root of the corresponding ratio R\,μ μ /eeZ R Z μ μ / e e for the Z boson measured in inclusive Z→ ee Z → e e and Z→ μ μ Z → μ μ events. By using the precise value of R\,μ μ /eeZ R Z μ μ / e e determined from e⁺e⁻ e + e - colliders, the ratio R\,μ /eW R W μ / e is determined to be aligned R\,μ /eW&= 0.9995± 0.0022\,(stat)\,± 0.0036\,(syst)\\ & ± 0.0014\,(ext) . aligned R W μ / e = 0.9995 ± 0.0022 ( stat ) ± 0.0036 ( syst ) ± 0.0014 ( ext ) . The three uncertainties correspond to data statistics, experimental systematics and the external measurement of R\,μ μ /eeZ R Z μ μ / e e , 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.