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

2 Collaboration

doi:10.1016/S0370-2693(99)00919-3

paper

First observation of the $ϕ \to π^{+} π^{-} γ$ decay

arXiv:hep-ex/9907005 · doi:10.1016/S0370-2693(99)00919-3

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 $e^{+} e^{-} \to π^{+} π^{-} γ$ events the $ϕ \to π^{+} π^{-} γ$ 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 $B r (ϕ \to f_{0} (980) γ) = (1.93 \pm 0.46 \pm 0.50) \times 1 0^{- 4}$ . \par Selected $e^{+} e^{-} \to μ^{+} μ^{-} γ$ events were used to obtain $B r (ϕ \to μ^{+} μ^{-} γ) = (1.43 \pm 0.45 \pm 0.14) \times 1 0^{- 5}$ 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 $ϕ$ : $B r (ϕ \to ρ γ) < 1.2 \times 1 0^{- 5}$ ; and for the P- and CP-violating decay of the $η$ : \par $B r (η \to π^{+} π^{-}) < 3.3 \times 1 0^{- 4}$ .

arXiv comment16 pages, 10 figures, Submitted to Phys. Lett. B

First observation of the $ϕ \to π^{+} π^{-} γ$ decay

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First observation of the $ϕ \to π^{+} π^{-} γ$ decay