Status of electroweak tests with heavy quarks

Abstract

The measurements of the partial decay-widths and forward-backward asymmetries for Z ! b b and Z ! c c test the Z couplings to the initial state e + e pair and the heavy quarks in the nal state. The four LEP detectors have registered about four million hadronic Z decays each and SLD at SLC has recorded 300000 Z decays with highly polarised electron beams. The high statistics as well as the good tracking, vertexing and particle identication capabilities of the detectors allow high precision measurements of these quantities. The measurements of the electroweak observables with heavy quarks are reviewed. The results of the dierent analyses are combined and interpreted within the framework of the Standard Model of electroweak interactions. In all cases good agreement with the Standard Model predictions is found, severely limiting the room for modications of these quantities from new physics.

Physics of Electroweak Gauge Bosons

“…If, however, the beamstrahlung in the Z-scan to calibrate the beam energy is the same as in the peak running it gets absorbed into an apparent shift of the calibration constants and basically no beamstrahl corrections for A LR are needed. It will be thus assumed that the linear collider can measure A LR with a final precision of 10 −4 corresponding to ∆ sin 2 θ ℓ eff = 0.000013 A b can be measured from the left-right-forward-backward asymmetry with similar methods as the ones used by LEP and SLD [16]. If the lepton and the jetcharge methods from LEP are taken as a reference a statistical error of ∆A b ∼ 5 · 10 −4 is possible for both methods.…”

Review of the Weak Mixing Angle Results with Heavy Quarks at LEP and SLC

“…In e + e − −annihilation four observables can be measured for any given fermion: the total cross section, the forward-backward asymmetry and the final state polarization together with its forward-backward asymmetry [2]. In the case of final state quarks, the two latter are not accessible.…”

“…Apart from corrections for the γ − Z interference and the photon exchange, additional corrections have to be applied to the born level formulas. They can be divided into three classes [2]:…”

Measurement of the semileptonic branching ratio of charm hadrons produced in

“…Inclusive semileptonic branching ratios are a means to investigate the dynamics of heavy quark decays, and have been studied in much detail for bottom quarks [1]. The inclusive semileptonic branching ratio of charm hadrons has not previously been measured at LEP, even though it is an important input to a number of measurements performed at energies around the Z 0 resonance [2].…”