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

Abstract A measurement of the vector to pseudoscalar conversion decay ϕ → π 0 e + 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 − collisions at s ∼ m ϕ collected at the DAΦNE e + e − collider. These events were used to perform the first measurement of the transition form factor | F ϕ π 0 ( q 2 ) | and a new measurement of the branching ratio of the decay: BR ( ϕ → π 0 e + 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.