Seminare de DPNC
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Mercredi, 13. nov. 1996

17.00 - Auditoire Stuckelberg

Universite de Geneve
Departement de physique
nucleaire et corpusculaire
24, quai Ernest-Ansermet
1211 Geneva 4

Tel. 022 702 6273
Fax. 022 781 2192

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Sujet:		Measurement of the Left-Right Zbbar Coupling Asymmetry
   		using Jet Charge at SLD

Par:		Dr. Thomas Junk, CERN

Resume:		
The parity-violating parameter $A_b$, the asymmetry between the
left- and right-handed couplings of the $b$ quark to the $Z^0$
boson, has been measured
by analyzing the polarized forward-backward asymmetry of $b$ quarks
in $e^+e^-\rightarrow Z^0\rightarrow b\overline b$.
Data were taken at the Stanford Linear Accelerator
Center (SLAC), with the Stanford Large Detector (SLD),
which records the products of $e^+e^-$ interactions at a center
of mass energy $\sqrt{s}=91.2$ GeV/c$^2$ at the SLAC Linear Collider
(SLC).  The SLC/SLD experimental apparatus
provides a unique and ideal environment
for measuring electroweak asymmetries.
Heavy flavor decays of the $Z^0$ were identified inclusively
by taking advantage of the long lifetime
of $B$ hadrons, the small, stable SLC beam spot, and SLD's
precise tracking detectors.  The sign of the flight direction
of the $b$ quark in tagged events
was determined using a momentum-weighted
jet charge variable, in which the efficiency of correctly signing
events was extracted from the momentum-weighted charge in the
two hemispheres of each event.
>From the 1994--1995 sample of 3.6~pb$^{-1}$, having a
luminosity-weighted average $e^-$ polarization of~77.2\%,  and the
1993 sample of 1.8~pb$^{-1}$, having a luminosity-weighted polarization
of 63.1\%, the asymmetry parameter obtained is
$A_b=0.843\pm 0.046 (\mbox{stat.}) \pm 0.051 (\mbox{syst.})$.