${{\mathit Z}}$ ASYMMETRY PARAMETERS

For each fermion-antifermion pair coupling to the ${{\mathit Z}}$ these quantities are defined as
$\mathit A_{\mathit f}$ = ${2 {\it g}^{\it f}_{\it V} {\it g}^{\it f}_{\it A}\over ({\it g}^{\it f}_{\it V}){}^{2}+({\it g}^{\it f}_{\it A}){}^{2}}$
where ${\it g}^{\it f}_{\it V}$ and ${\it g}^{\it f}_{\it A}$ are the effective vector and axial-vector couplings. For their relation to the various lepton asymmetries see the note “The ${{\mathit Z}}$ boson” and ref. LEP-SLC 2006.

$\mathit A_{{{\mathit \mu}}}$

INSPIRE   JSON  (beta) PDGID:
S044AM
This quantity is directly extracted from a measurement of the left-right forward-backward asymmetry in ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ production at SLC using a polarized electron beam. This double asymmetry eliminates the dependence on the ${{\mathit Z}}-{{\mathit e}}-{{\mathit e}}$ coupling parameter $\mathit A_{{{\mathit e}}}$.
VALUE EVTS DOCUMENT ID TECN  COMMENT
$0.142$ $\pm0.015$ 16844 1
ABE
2001B
 SLD ${\it{}E}^{\it{}ee}_{\rm{}cm}$= $91.24$ GeV
• • We do not use the following data for averages, fits, limits, etc. • •
$0.153$ $\pm0.012$ 1.7M 2
AAD
2015BT
 ATLS ${\it{}E}^{\it{}pp}_{\rm{}cm}$ = 7 TeV
1  ABE 2001B obtain this direct measurement using the left-right production and left-right forward-backward polar angle asymmetries in ${{\mathit \mu}^{+}}{{\mathit \mu}^{-}}$ decays of the ${{\mathit Z}}$ boson obtained with a polarized electron beam.
2  AAD 2015BT study ${{\mathit p}}$ ${{\mathit p}}$ $\rightarrow$ ${{\mathit Z}}$ $\rightarrow$ ${{\mathit \ell}^{+}}{{\mathit \ell}^{-}}$ events where ${{\mathit \ell}}$ is an electron or a muon in the dilepton mass region $70 - 1000$ GeV. The background in the ${{\mathit Z}}$ peak region is estimated to be $<$ 1$\%$ for the muon channel. The muon asymmetry parameter is derived from the measured forward-backward asymmetry assuming the value of the quark asymmetry parameter from the SM. For this reason it is not used in the average.
References