New results on weak decays of charmed mesons

Results of a study of the exclusive semileptonic decay modes D⁰→K^-e⁺ν_e and D⁺→K^-π⁺e⁺ν_e are presented. We have measured their branching fractions relative to those of dominant hadronic modes, BF(D⁰→K^-e⁺ν_e)/BF(D⁰→K^-π⁺)=0.91±0.07 ±0.11 and BF(D⁺→K*e⁺ν_e)/BF(D⁺→K^-π⁺π⁺) =0.53±0.05±0.06. The non-resonant Kπ component in the D⁺→Kπeν decay mode was found to be small. Combining our results with measurements with the D⁰ lifetime and a branching fraction for the mode D⁰→K^-π⁺ we find ‖V_cs‖²≡f₊(0)‖²=0.50±0.07±0.08. We have observed signals for decays D⁺_s and D⁺→π^-π⁺π⁺. We have analysed these modes for the fraction due to ρ⁰π⁺ and f₀(975)π⁺ and measured their relative branching fractions. Also, we present limits on flavour-changing neutral current decays D⁰→e⁺e^- and D⁰→μe.