Improved Direct Measurement of $A_b$ and $A_c$ at the $Z^0$ Pole Using a Lepton Tag

TL;DR

This paper reports precise measurements of the parity violation parameters $A_b$ and $A_c$ at the $Z^0$ pole using polarized electron beams and advanced lepton tagging techniques, improving the understanding of electroweak couplings.

Contribution

It introduces new multivariate analysis methods for lepton tagging, leading to more accurate direct measurements of $A_b$ and $A_c$ at the $Z^0$ pole.

Findings

Measured $A_b = 0.919 \, ext{with uncertainties}$

Measured $A_c = 0.583 \, ext{with uncertainties}$

Utilized polarized electron beams and semileptonic decay tagging.

Abstract

The parity violation parameters $A_b$ and $A_c$ of the $Zb{\bar b}$ and $Zc\bar{c}$ couplings have been measured directly, using the polar angle dependence of the polarized cross sections at the $Z^0$ pole. Bottom and charmed hadrons were tagged via their semileptonic decays. Both the electron and muon analyses take advantage of new multivariate techniques to increase the analyzing power. Based on the 1993-98 SLD sample of 550,000 $Z^0$ decays produced with highly polarized electron beams we measure $ A_b = 0.919 \pm 0.030_{stat} \pm 0.024_{syst} $, and $ A_c = 0.583 \pm 0.055_{stat} \pm 0.055_{syst} $.