Abstract
Current methods to extract the quark-mixing matrix element \$|V\_tb|\$ from
single-top production measurements assume that \$|V\_tb||V\_td|,
|V\_ts|\$: top quarks decay into \$b\$ quarks with 100\% branching fraction,
s-channel single-top production is always accompanied by a \$b\$ quark and
initial-state contributions from \$d\$ and \$s\$ quarks in the \$t\$-channel
production of single top quarks are neglected. Triggered by a recent
measurement of the ratio
\$R=|V\_tb|^2|V\_td|^2+|V\_ts|^2+|V\_tb|^2=0.90 0.04\$
performed by the D0 collaboration, we consider a \$|V\_tb|\$ extraction method
that takes into account non zero d- and s-quark contributions both in
production and decay. We propose a strategy that allows to extract consistently
and in a model-independent way the quark mixing matrix elements \$|V\_td|\$,
\$|V\_ts|\$, and \$|V\_tb|\$ from the measurement of \$R\$ and from single-top
measured event yields. As an illustration, we apply our method to the Tevatron
data using a CDF analysis of the measured single-top event yield with two jets
in the final state one of which is identified as a \$b\$-quark jet. We constrain
the \$|V\_tq|\$ matrix elements within a four-generation scenario by combining
the results with those obtained from direct measurements in flavor physics and
determine the preferred range for the top-quark decay width within different
scenarios.
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