Measurement of the Forward-Backward Asymmetries of e+e- -> Z -> b bbar and e+e- -> Z -> c cbar using prompt leptons

TL;DR

This paper reports precise measurements of forward-backward asymmetries in Z boson decays to b and c quarks, using data from the DELPHI experiment, to determine the weak mixing angle with high accuracy.

Contribution

It provides new measurements of asymmetries and the weak mixing angle by combining data from multiple years, improving the precision of electroweak parameters.

Findings

Measured A_FB^{0,b} = 0.1021 +/- 0.0052 (stat) +/- 0.0024 (syst)

Measured A_FB^{0,c} = 0.0728 +/- 0.0086 (stat) +/- 0.0063 (syst)

Derived sin^2 theta_{W,eff}^{lept} = 0.23170 +/- 0.00097

Abstract

The forward-backward asymmetries of the processes e+e- -> Z -> b bbar and e+e- -> Z -> c cbar were measured from a sample of hadronic Z decays collected by the DELPHI experiment between 1993 and 1995. Enriched samples of b bbar and c cbar events were obtained using lifetime information. The tagging of b and c quarks in these samples was based on the semileptonic decay channels b/c -> X + mu and b/c -> X + e combined with charge flow information from the hemisphere opposite to the lepton. Combining the A_{FB}^{b bbar} and A_{FB}^{c cbar} measurements presented in this paper with published results based on 1991 and 1992 DELPHI data samples, the following pole asymmetries were obtained: A_{FB}^{0,b} = 0.1021 +/- 0.0052 (stat) +/- 0.0024 (syst) A_{FB}^{0,c} = 0.0728 +/- 0.0086 (stat) +/- 0.0063 (syst) The effective value of the weak mixing angle derived from these measurements is sin^2 theta_{W,eff}^{lept} = 0.23170 +/- 0.00097 .