The first observation of the production of a $W$ boson
with a single charm quark ($c$) jet in $p\bar{p}$ collisions
at $s**(1/2)=1.96~{\rm TeV}$ is reported. The analysis uses data
corresponding to $4.3$~fb${-1}$, recorded with the CDF~II detector at
the Fermilab Tevatron. Charm quark candidates are selected through the
identification of an electron or muon from charm-hadron semileptonic
decay within a hadronic jet, and a $Wc$ signal is observed with a
significance of 5.7 standard deviations. The production cross section
$\sigma_{Wc}\left(p_{Tc}>20~{\rm GeV}/c,~|\eta_c|<1.5\right)\times
B(W--> \ell\nu)$ is measured to be $13.6{+3.4}_{-3.1}~{\rm pb}$
and is in agreement with theoretical expectations. From this result
the magnitude of the quark-mixing matrix element $V_{cs}$ is derived,
$|V_{cs}|=1.08+-0.16$ along with a lower limit of $|V_{cs}|>0.71$ at
the 95\% confidence level, assuming that the $Wc$ production through $c$
to $s$ quark coupling is dominant.
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Updated: Thursday, 2013 February 21 15:49:36 CST automatically from input from Barbara Hehner