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Register a new userObtaining the strong coupling constants g_{J/psi D_s D_s} and g_{phi D_s D_s} from QCD Sum Rules
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The form factors and coupling constants of the meson vertices J/psi D_s D_s and phi D_s D_s were calculated using three point correlation functions within the QCD Sum Rules formalism. We have considered the cases where phi, D_s and J/psi mesons are off-shell obtaining, for each vertex, two different form factors and its corresponding coupling constants, namely g_{J/psi D_s D_s} = 6.20^{+0.97}_{-1.15} and g_{phi D_s D_s} = 1.85^{+0.22}_{-0.23}.
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In this work, we calculate the form factors and the coupling constant of the strange-charmed vertex $J/psi D_s^* D_s$ in the framework of the QCD sum rules by studying their three-point correlation functions. All the possible off-shell cases are considered, $D_s$, $D_s^*$ and $J/psi$, resulting in three different form factors. These form factors are extrapolated to the pole of their respective off-shell mesons, giving the same coupling constant for the process. Our final result for the $J/psi D_s^* D_s$ coupling constant is $g_{J/psi D^*_s D_s} = 4.30^{+0.42}_{-0.37}text{GeV}^{-1}$.
We calculate the strong form factors and coupling constants of $ D^* D_s K$ and $D_s^* D K$ vertices using the QCD sum rules technique. In each case we have considered two different cases for the off-shell particle in the vertex: the ligthest meson and one of the heavy mesons. The method gives the same coupling constant for each vertex. When the results for different vertices are compared, they show that the SU(4) symmetry is broken by around 40%.
We have observed $23.2 pm 6.0_{-0.9}^{+1.0}$ purely-leptonic decays of $D_s^+ -> mu^+ u_mu$ from a sample of muonic one prong decay events detected in the emulsion target of Fermilab experiment E653. Using the $D_s^+ -> phi mu^+ u_mu$ yield measured previously in this experiment, we obtain $B(D_s^+ --> mu^+ u_mu) / B(D_s^+ --> phi mu^+ u_mu) =0.16 pm 0.06 pm 0.03$. In addition, we extract the decay constant $f_{D_s}=194 pm 35 pm 20 pm 14 MeV$.
We calculate the coupling constants of $D^*D_sK$ and $D_s^*DK$ vertices using the QCD sum rules technique. We compare results obtained in the limit of SU(4) symmetry and found that the symmetry is broken on the order of 40%.
We make a detailed study on the $D_s$ meson leading-twist LCDA $phi_{2;D_s}$ by using the QCD sum rules within the framework of the background field theory. To improve the precision, its moments $langle xi^nrangle _{2;D_s}$ are calculated up to dimension-six condensates. At the scale $mu = 2{rm GeV}$, we obtain: $langle xi^1rangle _{2;D_s}= -0.261^{+0.020}_{-0.020}$, $langle xi^2rangle _{2;D_s} = 0.184^{+0.012}_{-0.012}$, $langle xi^3rangle _{2;D_s} = -0.111 ^{+0.007}_{-0.012}$ and $langle xi^4rangle _{2;D_s} = 0.075^{+0.005}_{-0.005}$. Using those moments, the $phi_{2;D_s}$ is then constructed by using the light-cone harmonic oscillator model. As an application, we calculate the transition form factor $f^{B_sto D_s}_+(q^2)$ within the light-cone sum rules (LCSR) approach by using a right-handed chiral current, in which the terms involving $phi_{2;D_s}$ dominates the LCSR. It is noted that the extrapolated $f^{B_sto D_s}_+(q^2)$ agrees with the Lattice QCD prediction. After extrapolating the transition form factor to the physically allowable $q^2$-region, we calculate the branching ratio and the CKM matrix element, which give $mathcal{B}(bar B_s^0 to D_s^+ ell u_ell) = (2.03^{+0.35}_{-0.49}) times 10^{-2}$ and $|V_{cb}|=(40.00_{-4.08}^{+4.93})times 10^{-3}$.
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