Studies of D semileptonic decays at CLEO-c

Included in this dissertation are three analyses on D semileptonic decays using the ψ (3770) → DD¯ data collected by the CLEO-c detector at the Cornell Electron Storage Ring. (1) Using a 281 pb−1 data sample, we report the first observation of D+ → ηe +νe. We also set upper limits for D+ → η\u27e +νe and D+ → &phis;e+ν e that are about 2 orders of magnitude more restrictive than those obtained by previous experiments. (2) Using the entire ψ (3770) → DD¯ data sample collected by the CLEO-c detector, corresponding to an integrated luminosity of 818 pb−1, we present studies of the decays D0 → K −e+νe, D0 → π−e +νe, D+ → [special characters omitted]e+νe, and D+ → π0 e+νe. By measuring the partial rates as a function of q2, we study the semileptonic form factors governing these transitions, and test unquenched Lattice QCD (LQCD). Our measurements of branching fractions and form factors are the most precise to date. Using unquenched LQCD calculations of the form factor magnitudes we extract the CKM matrix elements: : Vcd: = 0.234(6)(2)(25) and :Vcs: = 0.985(8)(7)(103), where the first uncertainties are statistical, the second systematic and the third from LQCD. Our measurement of :Vcs: is the most precise direct determination to date. Our measurement of : Vcd: is the most precise determination using semileptonic decays. (3) Using the CLEO-c 818 pb−1 of data, we present the first observation of the decay D+ → η\u27 e+νe. Our results also include an improved branching fraction measurement for D + → ηe+ν e, the first measurement of the D+ → ηe+νe form factor, and an upper limit for D + → &phis;e+ν e, which is about a factor of 2 more restrictive than our measurement using the initial 281 pb−1 of data