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تسجيل مستخدم جديدSearch for the weak decays $J/psi to D^{(*)}_{s}e u_{e}$
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Using a sample of $2.25times 10^8$ $J/psi$ events collected with the BESIII detector at the BEPCII collider, we search for the $J/psi$ semi-leptonic weak decay $J/psi to D^{-}_{s} e^{+} u_{e}+c.c.$ with a much higher sensitivity than previous searches. We also perform the first search for $J/psi to D^{*-}_{s} e^{+} u_{e}+c.c.$ 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 $mathcal{B}(J/psi to D^{-}_{s}e^{+} u_{e}+c.c.)<1.3times10^{-6}$ and $mathcal{B}(J/psi to {D^{*}_{s}}^{-}e^{+} u_{e}+c.c.)<1.8times10^{-6}$, respectively. Both are consistent with Standard Model predictions.
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^{-} +c.c.$. No significant signals are observed and the corresponding upper limits on the branching fractions at the $90%$ confidence level are determined to be $Br(J/psi to D^{0} e^{+}e^{-} +c.c.)< 8.5times 10^{-8}$ and $Br (psi(3686) to D^{0} e^{+}e^{-} +c.c.)<1.4times 10^{-7}$, respectively. Our limit on $Br(J/psi to D^{0} e^{+}e^{-} +c.c.)$ is more stringent by two orders of magnitude than the previous results, and the $Br(psi(3686) to D^{0} e^{+}e^{-} +c.c.)$ is measured for the first time.
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B(D^0 to pi^-e^+ u_e)=(0.295pm 0.004pm 0.003)%$. From a study of the differential decay rates we obtain the products of hadronic form factor and the magnitude of the CKM matrix element $f_{+}^K(0)|V_{cs}|=0.7172pm0.0025pm 0.0035$ and $f_{+}^{pi}(0)|V_{cd}|=0.1435pm0.0018pm 0.0009$. Combining these products with the values of $|V_{cs(d)}|$ from the SM constraint fit, we extract the hadronic form factors $f^K_+(0) = 0.7368pm0.0026pm 0.0036$ and $f^pi_+(0) = 0.6372pm0.0080pm 0.0044$, and their ratio $f_+^{pi}(0)/f_+^{K}(0)=0.8649pm 0.0112pm 0.0073$. These form factors and their ratio are used to test unquenched Lattice QCD calculations of the form factors and a light cone sum rule (LCSR) calculation of their ratio. The measured value of $f_+^{K(pi)}(0) |V_{cs(d)}|$ and the lattice QCD value for $f^{K(pi)}_+(0)$ are used to extract values of the CKM matrix elements of $|V_{cs}|=0.9601 pm 0.0033 pm 0.0047 pm 0.0239$ and $|V_{cd}|=0.2155 pm 0.0027 pm 0.0014 pm 0.0094$, where the third errors are due to the uncertainties in lattice QCD calculations of the form factors. Using the LCSR value for $f_+^pi(0)/f_+^K(0)$, we determine the ratio $|V_{cd}|/|V_{cs}|=0.238pm 0.004pm 0.002pm 0.011$, where the third error is from the uncertainty in the LCSR normalization. In addition, we measure form factor parameters for three different theoretical models that describe the weak hadronic charged currents for these two semileptonic decays. All of these measurements are the most precise to date.
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