| The quark mixing parameters are fundamental constants of the Standard Model of particle physics. They determine the nine weak-current quark coupling elements of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The extraction of the quark couplings is difficult because quarks are bound inside hadrons by the strong interaction. Studying semileptonic decays are the preferred way to determine the CKM matrix elements as the strong interaction binding effects are confined to the hadronic current.Charm semileptonic decays have been studied in detail because they provide es-sential inputs of the magnitudes of the CKM elements |Vcd| and|Vcs|, and a stringent test of the strong interaction effects in the decay amplitude. These effects of the strong inter-action in the hadronic current are parameterized by form factors that are calculable, for example, by lattice QCD and QCD sum rules. The couplings|Vcs| and |Vcd| are tightly constrained by the unitarity of the CKM matrix. Therefore, measurements of charm semileptonic decay rates and form factors rigorously test theoretical predictions. Both high-statistics and rare modes should be studied for a comprehensive understanding of charm semileptonic decays.Semileptonic decay D+ â†'ωe+ve is such a decay that measurements of this decay rates and form factors rigorously test theoretical predictions. The decay D+â†' ωe+ve was first observed by the CLEO-c experiment, while the corresponding form factors have not yet been measured due to limited statistics. The transition rate of the decay D+â†'ωe+ve depends on the charm-to-down-quark coupling |Vcd|, which is precisely known from unitarity of the CKM matrix. Neglecting the lepton mass, three dominant form factors contribute to the decay rate:two axial (A1,A2) and one vector (â…¤) form factor, which are functions of the square of the invariant mass of the lepton-neutrino system q2.The decay D+ â†'φe+ve has not yet been observed. The most recent experimental search was performed by the CLEO Collaboration in 2011 with a sample of an inte-grated luminosity of 818 pb-1 collected at the Ψ(3770) resonance. The upper limit of the decay rate was set to be 9.0 × 10-5 at the 90% confidence level (C.L.). Since the va-lence quarks ss of the φ meson are distinct from those of the D meson (cd), this process cannot occur in the absence of ω-φ mixing or a non-perturbative "weak annihilation" (WA) contribution. A measurement of the branching fraction can discriminate which process is dominant. For example, a study of the ratio of Ds+ â†'ωe+ve and Ds+â†'φe+ve concludes that any value of B(Ds+â†'ωe+ve) exceeding 2 x 10-4 is unlikely to be at-tributed to ω-φ mixing, and would provide evidence for non-perturbative WA effects. A search for the decay D+â†'φe+ve is helpful, since its dynamics is similar to that of the decay Ds+â†'ωe+ve.Using 2.92 fb-1 of electron-positron annihilation data collected at a center-of-mass energy of (?)= 3.773 GeV with the BESâ…¢ detector, we present an improved measure-ment of the branching fraction B(D+â†'ωe+ve)= (1.63 ± 0.11 ± 0.08) × 10-3. The parameters defining the corresponding hadronic form factor ratios at zero momentum transfer are determined for the first time; we measure them to be rv= 1.24±0.09±0.06 and r2= 1.06± 0.15± 0.05. The first and second uncertainties are statistical and sys-tematic, respectively. We also search for the decay D+â†'φe+ve. An improved upper limit B(D+â†'φe+ve)< 1.3 × 10-5 is set at 90% confidence level.Using a sample of 2.25 ×108 J|Ψ events collected with the BESâ…¢ detector at the BEPCII collider, we also search for the J|Ψ weak decay J|Ψ â†' Ds-+ve+c.c. with a much higher sensitivity than previous searches. We also perform the first search for J|Ψâ†'Ds*+ve+c.c. No significant excess of a signal above background is observed in either channel. At the 90% confidence level, the upper limits are determined to be B(J|Ψâ†'Ds-+ve+c.c.)< 1.3 × 10-6 and B(J|Ψâ†' Ds*-e+ve+c.c.)< 1.8 × 10-6, respectively. Both are consistent with Standard Model predictions. |
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