Search for the semileptonic decays $\hat{I}{ž}_c^0\to \hat{I}{ž}^0{\ell }^{+}{\ell }^{-}$ at Belle

Abstract

Using the full data sample of 980 ${\mathrm{fb}}^{-1}$ collected with the Belle detector at the KEKB asymmetric energy electron-positron collider, we report the results of the first search for the rare semileptonic decays $\hat{I}{ž}_c^0\to \hat{I}{ž}^0{\ell }^{+}{\ell }^{-}$ ($\ell =e$ or $\hat{I}¼)$. No significant signals are observed in the $\hat{I}{ž}^0{\ell }^{+}{\ell }^{-}$ invariant-mass distributions. Taking the decay $\hat{I}{ž}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+}$ as the normalization mode, we report 90\% credibility upper limits on the branching fraction ratios $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^0{e}^{+}{e}^{-})/\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+})<6.7\times 10^{-3}$ and $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^0\hat{I}{¼}^{+}\hat{I}{¼}^{-})/\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+})<4.3\times 10^{-3}$ based on the phase-space assumption for signal decays. The 90\% credibility upper limits on the absolute branching fractions of $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^0{e}^{+}{e}^{-})$ and $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^0\hat{I}{¼}^{+}\hat{I}{¼}^{-})$ are found to be $9.9\times 10^{-5}$ and $6.5\times 10^{-5}$, respectively.

8 pages, 4 figures, submitted to PRD