Study of $\hat{I}{›}_c^{+}\to \hat{I}›\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ and Test of Lepton Flavor Universality with $\hat{I}{›}_c^{+}\to \hat{I}›{\ell }^{+}\hat{I}{½}_{\ell }$ Decays

Abstract

The measurement of the Cabibbo-favored semileptonic decay $\hat{I}{›}_c^{+}\to \hat{I}›\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼$ is reported using $4.5{\mathrm{fb}}^{-1}$ of $e^{+}{e}^{-}$ annihilation data collected at center-of-mass energies ranging from 4.600~GeV to 4.699~GeV. The branching fraction of the decay is measured to be $\mathcal{B}(\hat{I}{›}_c^{+}\to \hat{I}›\hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼)=(3.48\pm 0.14_{stat.}\pm 0.10_{syst.})\%$, three times more precise than the prior world average result. Tests of lepton flavor universality using $\hat{I}{›}_c^{+}\to \hat{I}›{\ell }^{+}\hat{I}{½}_{\ell }$ ($\ell =e,\hat{I}¼$) decays are reported for the first time, based on measurements of the differential decay rates and the forward-backward asymmetries in separate four-momentum transfer regions. The results are compatible with Standard Model predictions. Furthermore, we improve the determination of the form-factor parameters in $\hat{I}{›}_c^{+}\to \hat{I}›{\ell }^{+}\hat{I}{½}_{\ell }$ decays, which provide stringent tests and calibration for lattice quantum chromodynamics (LQCD) calculations.

11 pages, 5 figures