A Measurement of Rb using a Double Tagging Method

TL;DR

This paper reports a precise measurement of the Z boson decay fraction to bottom quarks (Rb) using a double tagging method, reducing systematic uncertainties and confirming Standard Model predictions.

Contribution

The study introduces a double tagging technique to measure Rb with minimized systematic uncertainties and detailed understanding of efficiency correlations.

Findings

Measured Rb = 0.2178 ± 0.0011 ± 0.0013

Results agree with Standard Model prediction of 0.2155 ± 0.0003

Systematic uncertainties are effectively controlled through data-simulation comparisons

Abstract

The fraction of Z to bbbar events in hadronic Z decays has been measured by the OPAL experiment using the data collected at LEP between 1992 and 1995. The Z to bbbar decays were tagged using displaced secondary vertices, and high momentum electrons and muons. Systematic uncertainties were reduced by measuring the b-tagging efficiency using a double tagging technique. Efficiency correlations between opposite hemispheres of an event are small, and are well understood through comparisons between real and simulated data samples. A value of Rb = 0.2178 +- 0.0011 +- 0.0013 was obtained, where the first error is statistical and the second systematic. The uncertainty on Rc, the fraction of Z to ccbar events in hadronic Z decays, is not included in the errors. The dependence on Rc is Delta(Rb)/Rb = -0.056*Delta(Rc)/Rc where Delta(Rc) is the deviation of Rc from the value 0.172 predicted by the Standard Model. The result for Rb agrees with the value of 0.2155 +- 0.0003 predicted by the Standard Model.