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The presently available high-statistics data of the D 0 → K 0 S π + π − processes measured by the Belle and BABAR Collaborations are analyzed within a quasi two-body factorization framework. Starting from the weak effective Hamiltonian, tree and annihilation amplitudes build up the D 0 → K 0 S π + π − decay amplitude. Two of the three final-state mesons are assumed to form a single scalar, vector or tensor state originating from a quark-antiquark pair so that the factorization hypothesis can be applied. The meson-meson final state interactions are described by Kπ and ππ scalar and vector form factors for the S and P waves and by relativistic Breit-Wigner formulae for the D waves. A combined χ 2 fit to a Belle Dalitz plot density distribution, to the total experimental branching fraction and to the τ − → K 0 S π − ντ decay data is carried out to fix the 33 free parameters. These are mainly related to the strengths of the scalar form factors and to unknown meson to meson transition form factors at a large momentum transfer squared equal to the D 0 mass squared. A good overall agreement to the Belle Dalitz plot density distribution is achieved. Another set of parameters fits equally well the BABAR Collaboration Dalitz plot model. The parameters of both fits are close, following from similar Dalitz density distribution data for both collaborations. The corresponding one-dimensional effective mass distributions display the contributions of the ten quasi two-body channels entering our D 0 → K 0 S π + π − decay amplitude. The branching fractions of the dominant channels compare well with those of the isobar Belle or BABAR models. The lower-limit values of the branching fractions of the annihilation amplitudes are significant. Built upon experimental data from other processes, the unitary Kπ and ππ scalar form factors, entering our decay amplitude and satisfying analyticity and chiral symmetry constraints, are furthermore constrained by the present Dalitz plot analysis. Our D 0 → K 0 S π + π − decay amplitude could be a useful input for determinations of D 0 -D 0 mixing parameters and of the CKM angle γ (or φ3).
The presently available high-statistics data of the D 0 → K 0 S π + π − processes measured by the Belle and BABAR Collaborations are analyzed within a quasi two-body factorization framework. Starting from the weak effective Hamiltonian, tree and annihilation amplitudes build up the D 0 → K 0 S π + π − decay amplitude. Two of the three final-state mesons are assumed to form a single scalar, vector or tensor state originating from a quark-antiquark pair so that the factorization hypothesis can be applied. The meson-meson final state interactions are described by Kπ and ππ scalar and vector form factors for the S and P waves and by relativistic Breit-Wigner formulae for the D waves. A combined χ 2 fit to a Belle Dalitz plot density distribution, to the total experimental branching fraction and to the τ − → K 0 S π − ντ decay data is carried out to fix the 33 free parameters. These are mainly related to the strengths of the scalar form factors and to unknown meson to meson transition form factors at a large momentum transfer squared equal to the D 0 mass squared. A good overall agreement to the Belle Dalitz plot density distribution is achieved. Another set of parameters fits equally well the BABAR Collaboration Dalitz plot model. The parameters of both fits are close, following from similar Dalitz density distribution data for both collaborations. The corresponding one-dimensional effective mass distributions display the contributions of the ten quasi two-body channels entering our D 0 → K 0 S π + π − decay amplitude. The branching fractions of the dominant channels compare well with those of the isobar Belle or BABAR models. The lower-limit values of the branching fractions of the annihilation amplitudes are significant. Built upon experimental data from other processes, the unitary Kπ and ππ scalar form factors, entering our decay amplitude and satisfying analyticity and chiral symmetry constraints, are furthermore constrained by the present Dalitz plot analysis. Our D 0 → K 0 S π + π − decay amplitude could be a useful input for determinations of D 0 -D 0 mixing parameters and of the CKM angle γ (or φ3).
In this work, we proceed to study the CP asymmetry in the angular distributions of τ → KSπντ decays within a general effective field theory framework including four-fermion operators up to dimension-six. It is found that, besides the commonly considered scalar-vector interference, the tensor-scalar interference can also produce a non-zero CP asymmetry in the angular distributions, in the presence of complex couplings. Using the dispersive representations of the Kπ form factors as inputs, and taking into account the detector efficiencies of the Belle measurement, we firstly update our previous SM predictions for the CP asymmetries in the same four Kπ invariant-mass bins as set by the Belle collaboration. Bounds on the effective couplings of the non-standard scalar and tensor interactions are then obtained under the combined constraints from the CP asymmetries measured in the four bins and the branching ratio of τ−→ KSπ−ντ decay, with the numerical results given respectively by $$ \operatorname{Im}\left[{\hat{\upepsilon}}_S\right] $$ Im ϵ ̂ S = −0.008 ± 0.027 and $$ \operatorname{Im}\left[{\hat{\upepsilon}}_T\right] $$ Im ϵ ̂ T = 0.03 ± 0.12, at the renormalization scale μτ = 2 GeV in the $$ \overline{\mathrm{MS}} $$ MS ¯ scheme. Using the best-fit values, we also find that the distributions of the CP asymmetries can deviate significantly from the SM expectation in almost the whole Kπ invariant-mass region. Nevertheless, the current bounds on $$ \operatorname{Im}\left[{\hat{\upepsilon}}_S\right] $$ Im ϵ ̂ S and $$ \operatorname{Im}\left[{\hat{\upepsilon}}_T\right] $$ Im ϵ ̂ T are still plagued by large experimental uncertainties, but will be improved with more precise measurements from the Belle II experiment as well as the proposed Tera-Z and STCF facilities. Assuming further that the non-standard scalar and tensor interactions originate from a weakly-coupled heavy new physics well above the electroweak scale, the SU(2)L invariance of the resulting SMEFT Lagrangian would indicate that very strong limits on $$ \operatorname{Im}\left[{\hat{\upepsilon}}_S\right] $$ Im ϵ ̂ S and $$ \operatorname{Im}\left[{\hat{\upepsilon}}_T\right] $$ Im ϵ ̂ T could also be obtained from the neutron electric dipole moment and the $$ {D}^0-{\overline{D}}^0 $$ D 0 − D ¯ 0 mixing. With the bounds from these processes taken into account, it is then found that, unless there exist extraordinary cancellations between the new physics contributions, neither the scalar nor the tensor interaction can produce any significant effects on the CP asymmetries (relative to the SM predictions) in the processes considered, especially under the “single coefficient dominance” assumption.
We study the contributions of the resonant states K * 0 (1430) and K * 0 (1950) in the three-body decays B → Kπh (with h = π, K) in the perturbative QCD approach. The crucial nonperturbative input F Kπ (s) in the distribution amplitudes of the S-wave Kπ system is derived from the matrix element of vacuum to Kπ pair. The CP averaged branching fraction of the quasi-two-body decay process B → K * 0 (1950)h → Kπh is about one order smaller than that of the corresponding decay B → K * 0 (1430)h → Kπh. In view of the important contribution from the S-wave Kπ system for the B → Kπh decays, it is not appropriate to neglect the K * 0 (1950) in the theoretical or experimental studies for the relevant three-body B meson decays. The predictions in this work for the relevant decays are consistent with the existing experimental data.
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