First observation of the $ϕ\toπ^+π^-γ$ decay

Abstract

Radiative decays of the $ϕ$ meson have been studied using a data sample of about 20 million $ϕ$ decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From selected $e^+e^-\toπ^{+}π^{-}γ$ events the $ϕ\toπ^{+}π^{-}γ$ decay has been observed for the first time. \par Under the assumption that the intermediate $f_{0}(980)γ$ state dominates in the $ϕ\to π^+π^-γ$ decay, the corresponding branching ratio is $Br(ϕ\to f_{0}(980)γ)=(1.93\pm 0.46\pm 0.50)\times10^{-4}$. \par Selected $e^+e^-\toμ^+μ^-γ$ events were used to obtain $Br(ϕ\toμ^+μ^-γ) =(1.43\pm 0.45\pm 0.14)\times10^{-5}$ for $E_γ>20$ MeV. \par Using the same data sample, upper limits at 90% CL have been obtained for the C-violating decay of the $ϕ$: $Br(ϕ\toργ) < 1.2\times10^{-5}$; and for the P- and CP-violating decay of the $η$: \par $Br(η\toπ^+π^-) < 3.3\times10^{-4}$.

16 pages, 10 figures, Submitted to Phys. Lett. B