Measurement of the $\ddot{I}•\to \ddot{I}{€}^0{e}^{+}{e}^{-}$ transition form factor with the KLOE detector

Abstract

A measurement of the vector to pseudoscalar conversion decay $\ddot{I}•\to \ddot{I}{€}^0{e}^{+}{e}^{-}$ with the KLOE experiment is presented. A sample of $\sim 9500$ signal events was selected from a data set of 1.7 fb${}^{-1}$ of $e^{+}{e}^{-}$ collisions at $\sqrt{s}\sim m_{\ddot{I}}•$ collected at the DA$\hat{I}¦$NE $e^{+}{e}^{-}$ collider. These events were used to obtain the first measurement of the transition form factor $|F_{\ddot{I}•\ddot{I}{€}^0}(q^2)|$ and a new measurement of the branching ratio of the decay: $\mathrm{BR}(\ddot{\mathrm{I}}•\to \ddot{\mathrm{I}}{€}^0{\mathrm{e}}^{+}{\mathrm{e}}^{-})=(1.35\pm 0.05_{-0.10}^{+0.05})\times 10^{-5}$. The result improves significantly on previous measurements and is in agreement with theoretical predictions.

13 pages, 4 figures; matches published version