Upper limit on the $\hat{I}\cdot \to \ddot{I}{€}^{+}\ddot{I}{€}^{-}$ branching fraction with the KLOE experiment

Abstract

Based on an integrated luminosity of 1.61 fb${}^{-1}$ $e^{+}{e}^{-}$ collision data collected with the KLOE detector at DA$\hat{I}¦$NE, the Frascati $\ddot{I}•$-factory, a search for the $P$- and $CP$-violating decay $\hat{I}\cdot \to \ddot{I}{€}^{+}\ddot{I}{€}^{-}$ has been performed. Radiative $\ddot{I}•\to \hat{I}\cdot {\hat{I}}^3$ decay is exploited to access the $\hat{I}\cdot$ mesons. No signal is observed in the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ invariant mass spectrum, and the upper limit on the branching fraction at 90\% confidence level is determined to be $\mathcal{B}(\hat{I}\cdot \to \ddot{I}{€}^{+}\ddot{I}{€}^{-})<4.9\times 10^{-6}$, which is approximately three times smaller than the previous KLOE result. From the combination of these two measurements we get $\mathcal{B}(\hat{I}\cdot \to \ddot{I}{€}^{+}\ddot{I}{€}^{-})<4.4\times 10^{-6}$ at 90\% confidence level.

11 pages, 3 figures