Hietala, Justin Thomas2015-04-092015-04-092014-12https://hdl.handle.net/11299/171127University of Minnesota Ph.D. dissertation. December 2014. Major: Physics. Major: Daniel Cronin-Hennessy. 1 computer file (PDF); xxxvii, 306 pages.We measure six exclusive Ds semileptonic branching ratios using CLEO-c data collected at 4170 MeV. We isolate our semileptonic events by reconstructing a tagged Ds to identify a Ds*Ds event, then we find an electron and the semileptonic hadron. Dropping the Ds* daughter photon gives us additional events and avoids the need to model soft photon backgrounds, at the expense of a clean neutrino missing mass. We obtain BR(Ds→φeν) = (2.14±0.17±0.09)% and BR(Ds→ηeν) = (2.28±0.14±0.20)% for the two largest branching ratios.enDsDs, D_s, D_{s}ExclusiveSemileptonicPhysicsThesis or Dissertation