Observation of B → ψπ decays

Abstract We have found the first evidence for the Cabibbo suppressed, color suppressed decay B − → ψπ − in a data sample of 4 million B decays obtained by the CLEO detector at the Cornell Electron Storage Ring (CESR). The branching ratio is found to be (4.3±2.3)% of the Cabibbo allowed B − → ψK − decay mode, which is consistent with theoretical expectations.