Abstract
Charm semileptonic decays allow a validation of lattice QCD calculations through the measurement of the hadronic form factors, which characterize the effect of strong interaction in these reactions. The accuracy of such calculations is crucial for the improvement of the test of the standard model in flavor physics. This thesis presents a study of the Ds+ → K+K-e+ve channel using 214 fb-1 recorded by de BAbar experiment. For events with a K+K- mass in the range between 1.01 GeV/c2 and 1.03 Gev/c2, the Φ → K+K- is the dominant component. Using the simple pole model to parameterize the q2 dependence of the form factors -V(q2), A1(q2) and A2(q2)- the following ratios are measured at q2 = 0; τV = V(0)/A1(0) = 1.868 ± 0.061 ± 0.079, r2 = A2(0)/A1(0) = 0.763 ± 0.072 ± 0.062. The mass pole of the axial-vector form factor is also obtained: mA = (2.30-0.18+0.42 ± 0.21) GeV/c2. In the same mass range, the semileptonic branching fraction, relative to the Ds+ → Φπ+ channel, is measured, and the absolute normalization of the axial-vector form factor is extracted: A1(q2 = 0) and = 0.605 ± 0.012 ± 0.018 ± 0.018. The stated errors refer to the statistical, systematic and errors from external inputs, respectively. An S wave component in the K+K- system, possibly originating from a f0, is also studied through its interference with the Φ. An S wave component is observed for the first time in this decay channel with a 5σ significance.
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