Measurement of the ϕ → π0e+e− transition form factor with the KLOE detector

A measurement of the vector to pseudoscalar conversion decay ϕ→π0e+e−ϕ→π0e+e− with the KLOE experiment is presented. A sample of ∼9500 signal events was selected from a data set of 1.7 fb−1 of e+e−e+e− collisions at s∼mϕ collected at the DAΦNE e+e−e+e− collider. These events were used to perform the first measurement of the transition form factor |Fϕπ0(q2)||Fϕπ0(q2)| and a new measurement of the branching ratio of the decay: BR(ϕ→π0e+e−)=(1.35±0.05−0.10+0.05)×10−5. The result improves significantly on previous measurements and is in agreement with theoretical predictions.