First measurements of the branching fractions for the decay modes $\hat{I}{ž}_c^0\to \hat{I}›\hat{I}\cdot$ and $\hat{I}{ž}_c^0\to \hat{I}›\hat{I}{\cdot }^{\prime }$ and search for the decay $\hat{I}{ž}_c^0\to \hat{I}›\ddot{I}{€}^0$ using Belle and Belle II data

Abstract

Using data samples of 988.4 fb${}^{-1}$ and 427.9 fb${}^{-1}$ collected with the Belle and Belle II detectors, we present a study of the singly Cabibbo-suppressed decays $\hat{I}{ž}_c^0\to \hat{I}›\hat{I}\cdot$, $\hat{I}›\hat{I}{\cdot }^{\prime }$, and $\hat{I}›\ddot{I}{€}^0$. We observe the decay $\hat{I}{ž}_c^0\to \hat{I}›\hat{I}\cdot$ and find evidence for the decay $\hat{I}{ž}_c^0\to \hat{I}›\hat{I}{\cdot }^{\prime }$, with corresponding branching ratios determined to be $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}›\hat{I}\cdot )/\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+})=(4.16\pm 0.91\pm 0.23)\%$ and $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}›\hat{I}{\cdot }^{\prime })/\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+})=(2.48\pm 0.82\pm 0.12)\%$, respectively. We find no significant signal in the $\hat{I}{ž}_c^0\to \hat{I}›\ddot{I}{€}^0$ decay mode and set an upper limit at the 90% credibility level of $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}›\ddot{I}{€}^0)/\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+})<3.5\%$. Multiplying these ratios by the world-average branching fraction of the normalization channel, $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}{ž}^{-}\ddot{I}{€}^{+})=(1.43\pm 0.27)\%$, we obtain the absolute branching fractions of $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}›\hat{I}\cdot )=(5.95\pm 1.30\pm 0.32\pm 1.13)\times 10^{-4}$, $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}›\hat{I}{\cdot }^{\prime })=(3.55\pm 1.17\pm 0.17\pm 0.68)\times 10^{-4}$, and an upper limit at the 90% credibility level on the absolute branching fraction of $\mathcal{B}(\hat{I}{ž}_c^0\to \hat{I}›\ddot{I}{€}^0)<5.2\times 10^{-4}$. The quoted first and second uncertainties are statistical and systematic, respectively, while the third uncertainties arise from the branching fraction of the normalization mode. These results are consistent with most theoretical predictions and further the understanding of the underlying decay mechanisms.

11 pages, 4 figures