First test of Lepton Flavor Universality in the charmed baryon decays $\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}{\ell }^{+}\hat{I}{½}_{\ell }$ using data of the Belle experiment

Abstract

We present the first observation of the $\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ decay and present measurements of the branching fraction ratios of the $\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}{\ell }^{+}\hat{I}{½}_{\ell }$ decays compared to the reference mode $\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\ddot{I}{€}^{+}$, ($\ell =e$ or $\hat{I}¼$). This analysis is based on 89.5 fb${}^{-1}$, 711 fb${}^{-1}$, and 121.1 fb${}^{-1}$ data samples collected with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider at the center-of-mass energies of 10.52 GeV, 10.58 GeV, and 10.86 GeV, respectively. The $\hat{I}{\text{c◯}}_c^0$ signal yields are extracted by fitting $M_{\hat{I}{\text{c◯}}^{-}{\ell }^{+}}$ and $M_{\hat{I}{\text{c◯}}^{-}\ddot{I}{€}^{+}}$ spectra. The branching fraction ratios $\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}{e}^{+}\hat{I}{½}_e)/\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\ddot{I}{€}^{+})$ and $\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)/\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\ddot{I}{€}^{+})$ are measured to be $1.98\pm 0.13(stat.)\pm 0.08(syst.)$ and $1.94\pm 0.18(stat.)\pm 0.10(syst.)$, respectively. The ratio of $\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}{e}^{+}\hat{I}{½}_e)/\mathcal{B}(\hat{I}{\text{c◯}}_c^0\to \hat{I}{\text{c◯}}^{-}\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)$ is measured to be $1.02\pm 0.10(stat.)\pm 0.02(syst.)$, which is consistent with the expectation of lepton flavor universality.

7 pages, 3 figures, accepted for publication as a Letter in Physical Review D