Measurement of the semileptonic b branching fractions and average b mixing parameter in Z decays

TL;DR

This paper measures semileptonic b decay branching fractions and the b mixing parameter in Z decays using data from the DELPHI experiment at LEP, providing precise results and analysis techniques.

Contribution

It presents new measurements of b decay branching fractions and the b mixing parameter in Z decays, with detailed analysis and separation of decay types.

Findings

BR(b -> lepton-) = (10.70 +/- 0.08 +/- 0.21 +0.44/-0.30)%

BR(b -> c -> lepton+) = (7.98 +/- 0.22 +/- 0.21 +0.14/-0.20)%

chi-bar = 0.127 +/- 0.013 +/- 0.005 +/- 0.004

Abstract

The semileptonic branching fractions for primary and cascade b decays BR(b -> lepton-), BR(b -> c -> lepton+) and BR(b -> cbar -> lepton-) were measured in hadronic Z decays collected by the DELPHI experiment at LEP. The sample was enriched in b decays using the lifetime information and various techniques were used to separate leptons from direct or cascade b decays. By fitting the momentum spectra of di-leptons in opposite jets, the average b mixing parameter chi-bar was also extracted. The following results have been obtained: BR(b -> lepton-) = (10.70 +/- 0.08 (stat) +/- 0.21 (syst)_{+0.44}^{-0.30}(model))% BR(b -> c -> lepton+) = (7.98 +/- 0.22 (stat) +/- 0.21 (syst)^{+0.14}_{-0.20}(model))% BR(b -> cbar -> lepton-) = (1.61 +/- 0.20 (stat) +/- 0.17 (syst)^{+0.30}_{-0.44}(model))% chi-bar = 0.127 +/- 0.013 (stat) +/- 0.005 (syst) +/- 0.004(model)