Probing QCD dynamics and the standard model with $$ {D}_{(s)}^{+}\to {P}_1^{+}{P}_2^0\gamma $$ decays

We compute 10 radiative three-body decays of charged charmed mesons $$ {D}^{+}\to {P}_1^{+}{P}_2^0\gamma $$ D + → P 1 + P 2 0 γ and $$ {D}_s\to {P}_1^{+}{P}_2^0\gamma $$ D s → P 1 + P 2 0 γ , P1,2 = π, K, in leading order QCDF, HHχPT and the soft photon approximation. We work out decay distributions and asymmetries in the standard model and with new physics in the electromagnetic dipole operators. The forward-backward asymmetry is suitable to probe the QCD frameworks, in particular the s-channel dependent weak annihilation contributions in QCDF against the markedly different resonance structure in HHχPT. These studies can be performed with Cabibbo-favored modes Ds → π+π0γ, $$ {D}^{+}\to {\pi}^{+}{\overline{K}}^0\gamma $$ D + → π + K ¯ 0 γ and $$ {D}_s\to {K}^{+}{\overline{K}}^0\gamma $$ D s → K + K ¯ 0 γ with $$ \mathcal{O}\left({10}^{-4}-{10}^{-3}\right)\hbox{-} \mathrm{level} $$ O 10 − 4 − 10 − 3 ‐ level branching ratio, which are standard model-like and induced by different hadronic dynamics. Understanding of the latter can therefore be improved in a data-driven way and sharpens the interpretation of standard model tests. Singly Cabibbo-suppressed modes such as D+ → π+π0γ, Ds → π+K0γ, Ds → K+π0γ with branching ratios within ∼ 10−5–10−4 are sensitive to new physics that can be signalled in the forward-backward asymmetry and in the CP-asymmetry of the rate, ideally in the Dalitz region but also in single differential distributions. Results complement those with neutral D0→ P1P2γ decays.

Disentangling QCD and new physics in D → πℓ+ℓ−

In this paper we consider the decay D+ → π+ℓ+ℓ−, addressing in particular the resonance contributions as well as the relatively large contributions from the weak annihilation diagrams. For the weak annihilation diagrams we include known results from QCD factorisation at low q2 and at high q2, adapting the existing calculation for B decays in the Operator Product Expansion. The hadronic resonance contributions are obtained through a dispersion relation, modelling the spectral functions as towers of Regge-like resonances in each channel, as suggested by Shifman, imposing the partonic behaviour in the deep Euclidean. The parameters of the model are extracted using e+e− → (hadrons) and τ → (hadrons) + ντ data as well as the branching ratios for the resonant decays D+ → π+R(R → ℓ+ℓ−), with R = ρ, ω, and ϕ. We perform a thorough error analysis, and present our results for the Standard Model differential branching ratio as a function of q2. Focusing then on the observables FH and AFB, we consider the sensitivity of this channel to effects of physics beyond the Standard Model, both in a model independent way and for the case of leptoquarks.

The branching fraction calculations of Bc+ → ψ(2S)π+, Bc+ → J/ψK+ and Bc+ → J/ψDs+ decays relative to that of the Bc+ → J/ψπ+ mode

The weak decay of [Formula: see text] into [Formula: see text], [Formula: see text] and [Formula: see text] mesons, observed by LHCb collaboration for the first time, are calculated in the model which takes into account the “factorizable” contributions and “nonfactorizable” corrections. The decays of [Formula: see text] mesons into charmonia and light hadrons are expected to be well described by the factorization approximation. In the standard model, [Formula: see text], [Formula: see text] decays occur through only the tree-level diagrams and so there are no CP violation in these channels. The decay [Formula: see text] is expected to proceed mainly via a [Formula: see text] transition because the [Formula: see text] decay has identical final state and similar event topology, where it is chosen as the relative branching fraction channel. The ratio of branching fractions [Formula: see text] is of particular interest since the CKM matrix element is suppressed by a factor [Formula: see text], in which the [Formula: see text] occur through [Formula: see text] transition, but the dominant amplitude of the decay [Formula: see text] is a [Formula: see text] transition. The decay [Formula: see text] is examined by color-allowed, color-suppressed spectator and weak annihilation diagrams. The weak annihilation topology, in contrast to decays of other beauty hadrons, is not suppressed and can contribute significantly to the decay amplitude. Because of the [Formula: see text], [Formula: see text] and [Formula: see text] branching fractions are calculated relative to the [Formula: see text] decay, this decay mode is estimated separately, the ratio between them are [Formula: see text], [Formula: see text] and [Formula: see text], respectively, that are compatible with the experimental data.

Study of B+ c decays to the K+K−π+ final state by using B0 s , χc0 and D0 resonances and weak annihilation nonresonant topologys

In this research the weak decay ofBc+decays to theK+K−π+final state, which is being observed by LHCb collaboration for the first time, is calculated in the quasi-two-body decays which takes theBs0, χc0andD0resonances and weak annihilation nonresonant contributions into account. In this process, theBc+meson decays first intoBs0π+, χc0π+andD0π+intermediate states, and then theBs0, χc0andD0resonances decay intoK+K−components, which undergo final state interaction. The mode of theBc+ → D0(→K−π+)K+is also associated with the calculation, in this mode the intermediate resonanceD0decays to theK−π+final mesons. The resonancesBs0, χc0andD0effects in theBc+ → Bs0(→K+K−)π+,Bc+ → χc0(→K+K−)π+andBc+ → D0(→K+K−)π+,D0(→K−π+)K+decays are described in terms of the quasi-two-body modes. There is a weak annihilation nonresonant contribution in whichBc+decays to theK+K−π+directly, so the point-like 3-body matrix element$$ \left\langle {K}^{+}{K}^{-}{\pi}^{+}\left|u\overline{d}\right|0\right\rangle $$K+K−π+ud¯0is also considered. The decay mode of the$$ {B}_c^{+}\to {\overline{K}}^{\ast 0}(892){K}^{+} $$Bc+→K¯∗0892K+is contributed to the annihilation contribution. The branching ratios of quasi-two-body decays expand in the range of (2.12 ± 0.61) × 10−6to (7.56 ± 1.71) × 10−6.

CharmlessBc→PP,PVDecays in the QCD Factorization Approach

The charmlessBc→PP,PVdecays (wherePandVdenote the light pseudoscalar and vector mesons, resp.) can occur only via the weak annihilation diagrams within the Standard Model. In this paper, we study these kinds of decays in the framework of QCD factorization, by adopting two different schemes: scheme I is similar to the method usually adopted in the QCD factorization approach, while scheme II is based on the infrared behavior of gluon propagator and running coupling. For comparison, in our calculation, we adopt three kinds of wave functions forBcmeson. The branching ratios based on the two schemes are given. It is found that (a) the predicted branching ratios in scheme I are, however, quite small and almost impossible to be measured at the LHCb experiment and (b) in scheme II, by assigning a dynamical gluon mass to the gluon propagator, we can avoid enhancements of the contribution from soft endpoint region. The strength of annihilation contributions predicted in scheme II is enhanced compared to that obtained in scheme I.