The D_s-Meson Distribution Amplitude Under QCD Sum Rules And Its Application In The Semileptonic Decay B_s→D_slv

Mesonic distribution amplitudes are the key parameters for the theoretical study of the exclusive and inclusive processes invoving hadrons.Their accuracy directly affects the accuracy of theoretical predictions related to mesons.At present,the distribution amplitudes of light mesons such as pion and K meson have been well understood,but the distribution amplitudes of heavy quarks are still at a preliminary stage.In this paper,we systematically study the properties of the leading-twist distribution amplitude of the Ds meson based on the background field theory,and apply them to the calculation of transition form factors and semi-leptonic decay processes related to Ds mesons.Standard model parameters such as CKM matrix elements can be extracted by comparing the theoretical results and experimental measurements of such processes,which is significant to find new physical effects beyond the standard model.The existence of vacuum condensation terms is an important feature of quantum chromodynamics(QCD)theory,which plays an important role in understanding hadronic spectrum and hadronic physical processes.From the perspective of quantum field theory,the classical background field satisfying the QCD equation of motion is used to describe the non-perturbation effect,and the quantum fluctuation around the classical background field is described by the quantum field,namely the perturbation effect.The background field theory provides a clear physical image for QCD sum rules,a self-consistent theoretical basis for operator product expansion method and rigorous theoretical support for calculation of correlation function.Therefore,compared with traditional SVZ QCD sum rules,SVZ QCD sum rules has unique advantages in the calculation of propagators and vertices,derivation of vacuum matrix element formula and proof of mathematical completeness.In this paper,we use the QCD sum rules to study the tiwst-2 light cone distribution amplitude φ2:Ds:of Ds meson.In order to improve the accuracy of the theoretical calculation,the contribution of the six-dimensional condensation term is retained in the calculation of the moment of the light cone distribution amplitude,on the basis of considering the one-loop perturbation effect.At the scale μ=2GeV,we obtain:<ξ1>2:Ds=-0.261-0.02+0.02,<ξ2>2:Ds=0.184-0.012+0.012,<ξ3>2:Ds=-0.111-0.012+0.007 and<ξ4>2:Ds=0.075-0.005+0.005.Furthermore,we calculate the Gegenbauer moments based on the relation between the moments of the distribution amplitude and Gegenbauer moments.Using those moments,the input parameters involved in the harmonic oscillator model of φ2:Ds can be determined.As an application,we calculate the transition form factor f+Bs→Ds(q2)within the light-cone sum rules approach by using a right-handed chiral current.It is noted that after extrapolating the transition form factor to the large q2 region,the extrapolated f+Bs→Ds(q2)we obtained agrees with the lattice QCD prediction within errors.Based on this,we calculate the branching ratio B(Bs0→Ds+lvl)=(2.033-0.488+0.350)×10-2.Inversely,the CKM matrix elements can be determined by comparing with experimental values,|Vcb|=(40.00-4.08+4.93)×10-3,which is consistent well within the relativistic quark model prediction within errors.To some extent,the distribution amplitude φ2:Ds of Ds meson we obtained is reasonable.Subsequently,we recalculate the Bs→Ds transition form factors under the heavy quark effective field theory as the core factor of the semi-leptonic decay of Bs mesons.In heavy quark effective field theory,heavy quarks mainly interact by exchanging soft gluons with other light particles in heavy hadrons.Taking the heavy quark symmetry and heavy quark efficient theory into consideration,the physical process of heavy hadrons can be greatly simplified.In the work,we study the Bs→Ds transition form factors by adopting a chiral current correlation function to do the calculation,the resultant transition form factors f+Bs→Ds(q2)and f0Bs→Ds(q2)are dominated by the contribution of Ds-meson leading-twist distribution amplitude,while the contributions from less certain Ds-meson twist-3 distribution amplitudes are greatly suppressed.At the largest recoil point,we obtain f+,0Bs→Ds(q2)=0.533-0.094+0.112.By further extrapolating the transition form factors into all the physically allowable q2 region with the help of the z-series parametrization,the transition form factors we obtained are consistent with those obtained by the above methods within the error range,indicating that both methods can be used to deal with such non-perturbative transition form factors.Finally,we calculate the branching fractions B(Bs→Dsl’vl’ with l’=e,μ and B(Bs→Dsτvτ),which gives R(Ds)=0.334±0.017.