Measurement of the partial widths of the Z into up- and down-type quarks

TL;DR

This paper measures the partial decay widths of the Z boson into up- and down-type quarks using OPAL LEP1 data, providing results consistent with the Standard Model.

Contribution

It presents a novel measurement of Z boson decay widths into specific quark types using isolated photon tagging in hadronic decays.

Findings

Gamma u = 300^{+19}_{-18} MeV

Gamma d = 381^{+12}_{-12} MeV

Results agree with Standard Model predictions

Abstract

Using the entire OPAL LEP1 on-peak Z hadronic decay sample, Z -> qbarq gamma decays were selected by tagging hadronic final states with isolated photon candidates in the electromagnetic calorimeter. Combining the measured rates of Z -> qbarq gamma decays with the total rate of hadronic Z decays permits the simultaneous determination of the widths of the Z into up- and down-type quarks. The values obtained, with total errors, were Gamma u = 300 ^{+19}_{-18} MeV and Gamma d = 381 ^{+12}_{-12} MeV. The results are in good agreement with the Standard Model expectation.