${\rm Y}$ Dipion Transitions at Energies Near the ${\rm Y}(4S)$

Abstract

Using a data sample collected with the CLEO II detector at CESR, we have searched for dipion transitions between pairs of ${\rm Y}$ resonances at energies near the ${\rm Y}(4S)$. We obtain upper limits $B({\rm Y}(4S)\to {\rm Y}(2S){\pi }^{+}{\pi }^{-})<3.9\times 10^{-4}$ and $B({\rm Y}(4S)\to {\rm Y}(1S){\pi }^{+}{\pi }^{-})<1.2\times 10^{-4}$. We also observe the transitions ${\rm Y}(3S)\to {\rm Y}(1S)$, ${\rm Y}(3S)\to {\rm Y}(2S)$, and ${\rm Y}(2S)\to {\rm Y}(1S)$, from which we measure the cross-sections for the radiative processes $e^{+}{e}^{-}\to {\rm Y}(3S)\gamma$ and $e^{+}{e}^{-}\to {\rm Y}(2S)\gamma$.

17 pages, postscript file also available through http://w4.lns.cornell.edu/public/CLNS