Abstract
Using data recorded at centre-of-mass energies around 183 and 189 GeV with the OPAL detector at LEP, the fundamental coupling of the charm quark to the W boson has been studied. The ratio R c W ≡Γ ( W→ c X )/Γ ( W→ hadrons) has been measured from jet properties, lifetime information, and leptons produced in charm decays. A value compatible with the Standard Model expectation of 0.5 is obtained: R c W =0.481±0.042 (stat.) ±0.032 (syst.) . By combining this result with measurements of the W boson total width and hadronic branching ratio, the magnitude of the CKM matrix element | V cs| is determined to be | V cs|=0.969±0.058.
Highlights
Since 1997 the LEP e+e− collider has been operated at energies above the threshold for W-pair production
The data used for this analysis were recorded at LEP by the OPAL detector [3] at centre–of–mass energies around 183 GeV in 1997 and 189 GeV in 1998
Using data taken with the OPAL detector at LEP at centre–of–mass energies of 183 GeV and 189 GeV, the ratio RcW = Γ (W → c X)/Γ (W → hadrons) has been measured using a technique based on jet properties, lifetime information, and leptons from charm decays
Summary
Since 1997 the LEP e+e− collider has been operated at energies above the threshold for W-pair production This offers a unique opportunity to study the hadronic decays of W bosons in a clean environment and to investigate the coupling strength of W bosons to different quark flavours. The fraction of W bosons decaying hadronically to different quark flavours is proportional to the sum of the squared magnitudes of the corresponding elements of the Cabibbo–Kobayashi–Maskawa (CKM) matrix [1]. The production of bottom quarks is highly suppressed due to the small magnitude of |Vub| and |Vcb| and the large mass of the top quark, the weak partner of the bottom quark This allows for a direct measurement of the production fraction of charm in W decays without a separation of charm and bottom quarks. The measured value of RcW is used to determine |Vcs|
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