| Abstract |
content_type = "text/x-tex"
user_agent = "Mozilla/5.0 AppleWebKit/537.36 (KHTML, like Gecko; compatible; ClaudeBot/1.0; +claudebot@anthropic.com)"
moz = "Mozilla/5.0 "
moz_version = "5"
We report the first observation of $e^+e^-\ \rightarrow\ \rho^+\rho^-$,
in a data sample of 379~$\,fb^{-1}$\ collected with the
{\slshape B\kern-0.1em{A}\kern-0.1em B\kern-0.1em{A\kern-0.2em R}}\/
detector at the {PEP-II} $e^+e^-$ storage ring at center-of-mass energies near
$\sqrt{s}\! =$10.58$~$\mathrm{\,Ge\kern -0.1em V}$\ .
We measure a cross section of
$\sigma({e^+e^-\ }\!\! \rightarrow\! \rho^+ \rho^-)\! =
{19.5\pm 1.6 (\mathrm{stat})\pm 3.2(\mathrm{syst})~\mathrm{fb}}$.
Assuming production through single-photon annihilation, there are three
independent helicity amplitudes.
We measure the ratios of their squared moduli to be
$|{F}_{00}|^2:|{F}_{10}|^2:|{F}_{11}|^2=$ $0.51\pm0.14(\mathrm{stat})\pm0.07(\mathrm{syst}):0.10\pm0.04
(\mathrm{stat})\pm0.01(\mathrm{syst}):0.04\pm0.03(\mathrm{stat})\pm0.01(\mathrm{syst})$.
The $|{F}_{00}|^2$ result is inconsistent with the prediction of 1.0
made by QCD models with a significance of 3.1 standard deviations including
systematic uncertainties.
|
