We report the first observation of a_{0}^{0}(980)-f_{0}(980) mixing in the decays of J/ψ→ϕf_{0}(980)→ϕa_{0}^{0}(980)→ϕηπ^{0} and χ_{c1}→a_{0}^{0}(980)π^{0}→f_{0}(980)π^{0}→π^{+}π^{-}π^{0}, using data ...samples of 1.31×10^{9} J/ψ events and 4.48×10^{8} ψ(3686) events accumulated with the BESIII detector. The signals of f_{0}(980)→a_{0}^{0}(980) and a_{0}^{0}(980)→f_{0}(980) mixing are observed at levels of statistical significance of 7.4σ and 5.5σ, respectively. The corresponding branching fractions and mixing intensities are measured and the constraint regions on the coupling constants, g_{a_{0}K^{+}K^{-}} and g_{f_{0}K^{+}K^{-}}, are estimated. The results improve the understanding of the nature of a_{0}^{0}(980) and f_{0}(980).
We extract a relatively precise value for the decay constant of the D{sup +} meson by measuring B(D{sup +}{yields}{mu}{sup +}{nu})=(4.40{+-}0.66{sub -0.12}{sup +0.09})x10{sup -4} using 281 pb{sup -1} ...of data taken on the {psi}(3770) resonance with the CLEO-c detector. We find f{sub D{sup +}}=(222.6{+-}16.7{sub -3.4}{sup +2.8}) MeV, and compare with current theoretical calculations. We also set a 90% confidence upper limit on B(D{sup +}{yields}e{sup +}{nu})<2.4x10{sup -5} which constrains new physics models.
With the first data sample collected by the CLEO-c detector at the {psi}(3770) resonance we have studied four exclusive semileptonic decays of the D{sup 0} meson. Our results include the first ...observation and absolute branching fraction measurement for D{sup 0}{yields}{rho}{sup -}e{sup +}{nu}{sub e} and improved measurements of the absolute branching fractions for D{sup 0} decays to K{sup -}e{sup +}{nu}{sub e}, {pi}{sup -}e{sup +}{nu}{sub e}, and K*{sup -}e{sup +}{nu}{sub e}.
Using 55.8 pb{sup -1} of e{sup +}e{sup -} collisions recorded at the {psi}(3770) resonance with the CLEO-c detector at CESR, we determine absolute hadronic branching fractions of charged and neutral ...D mesons using a double tag technique. Among measurements for three D{sup 0} and six D{sup +} modes, we obtain reference branching fractions B(D{sup 0}{yields}K{sup -}{pi}{sup +})=(3.91{+-}0.08{+-}0.09)% and B(D{sup +}{yields}K{sup -}{pi}{sup +}{pi}{sup +})=(9.5{+-}0.2{+-}0.3)%, where the uncertainties are statistical and systematic, respectively. Final state radiation is included in these branching fractions by allowing for additional, unobserved, photons in the final state. Using a determination of the integrated luminosity, we also extract the cross sections {sigma}(e{sup +}e{sup -}{yields}D{sup 0}D{sup 0})=(3.60{+-}0.07{sub -0.05}{sup +0.07}) nb and {sigma}(e{sup +}e{sup -}{yields}D{sup +}D{sup -})=(2.79{+-}0.07{sub -0.04}{sup +0.10}) nb.
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