Abstract |
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We report the first observation of $e^+e^-$ annihilations into
states of positive $C$-parity,
namely $\rho^0 \rho^0$ and $\phi\rho^0$.
The two states
are observed in the $\pip\pim\pip\pim$ and $K^+K^-\pip\pim$
final states, respectively,
in a data sample of 225~$fb^{-1}$ collected by the $BaBar$~experiment at
the $PEP-II$ $e^+e^-$ storage rings at energies near
$\sqrt{s}\! ~=$ 10.58~$GeV$.
The distributions of $\cos\theta^*$, where $\theta^*$ is the center-of-mass polar angle of the $\phi$ meson or
the forward $\rho^0$ meson, suggest production by two-virtual-photon annihilation.
We measure cross sections within the range
$|\cos\theta^*|\! ~<~ \! 0.8$ of
$\sigma(\e^+e^-\!\! \to\! \rho^0 \rho^0)\! ~=~$$20.7 \pm 0.7 (\mathrm{stat})\pm 2.7(\mathrm{syst}) ~\mathrm{fb}$ and
$\sigma(\e^+e^-\!\! \to\! \phi \rho^0)\! ~=~$$5.7\pm 0.5(\mathrm{stat}) \pm 0.8(\mathrm{syst}) ~\mathrm{fb}$.
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