Measurement of $A_c$ with Charmed Mesons at SLD

TL;DR

This paper reports a precise measurement of the parity-violation parameter $A_c$ in $Z^0$ to charm quark couplings using data from the SLD detector, employing advanced tagging techniques to distinguish charm events.

Contribution

The study introduces a combined method of exclusive meson reconstruction and soft-pion tagging to measure $A_c$ with high accuracy, effectively separating charm signals from background.

Findings

Measured $A_c = 0.688 \, ext{±} \, 0.041$

Achieved efficient background separation using vertex information

Utilized a large sample of 530,000 hadronic $Z^0$ decays

Abstract

We present a direct measurement of the parity-violation parameter $A_c$ in the coupling of the $Z^0$ to $c$-quarks with the SLD detector. The measurement is based on a sample of 530k hadronic $Z^0$ decays, produced with a mean electron-beam polarization of $|P_e| = 73 %$. The tagging of $c$-quark events is performed using two methods: the exclusive reconstruction of $D^{\ast+}$, $D^+$, and $D^0$ mesons, and the soft-pions ($\pi_s$) produced in the decay of $D^{\ast+}\to D^0 \pi_s^+$. The large background from $D$ mesons produced in $B$ hadron decays is separated efficiently from the signal using precision vertex information. The combination of these two methods yields $A_c = 0.688 \pm 0.041.$