First observation of the φ→π+π−γ decay

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−→π+π−γ events the φ→π+π−γ decay has been observed for the first time. Under the assumption that the intermediate f0(980)γ state dominates in the φ→π+π−γ decay, the corresponding branching ratio is Br(φ→f0(980)γ)=(1.93±0.46±0.50)×10−4. Selected e+e−→μ+μ−γ events were used to obtain Br(φ→μ+μ−γ)=(1.43±0.45±0.14)×10−5 for Eγ>20 MeV. Using the same data sample, upper limits at 90% CL have been obtained for the C-violating decay of the φ: Br(φ→ργ)<1.2×10−5; and for the P- and CP-violating decay of the η: Br(η→π+π−)<3.3×10−4.