arXiv subjects

Hai-Yang Cheng

Publications and source records attributed to Hai-Yang Cheng.

At least 37 records · Page 2Linked to original sources

arXiv2022

Hadronic three-body D decays mediated by scalar resonances

We study the quasi-two-body $D\to SP$ decays and the three-body $D$ decays proceeding through intermediate scalar resonances, where $S$ and $P$ denote scalar and pseudoscalar mesons, respectively. Our main results are: (i) Certain external and internal $W$-emission diagrams with the emitted meson being a scalar meson are na{ï}vely expected to vanish, but they actually receive contributions from vertex and hard spectator-scattering corrections beyond the factorization approximation. (ii) For light scalars with masses below or close to 1~GeV, it is more sensible to study three-body decays directly and compare with experiment as the two-body branching fractions are either unavailable or subject to large finite-width effects of the scalar meson. (iii) We consider the two-quark (scheme I) and four-quark (scheme II) descriptions of the light scalar mesons, and find the latter generally in better agreement with experiment. This is in line with recent BESIII measurements of semileptonic charm decays that prefer the tetraquark description of light scalars produced in charmed meson decays. (iv) The topological amplitude approach fails here as the $D\to SP$ decay branching fractions cannot be reliably inferred from the measurements of three-body decays, mainly because the decay rates cannot be factorized into the topological amplitude squared and the phase space factor. (v) The predicted rates for $D^0\to f_0 P, a_0 P$ are generally smaller than experimental data by one order of magnitude, presumably implying the significance of $W$-exchange amplitudes. (vi) The $W$-annihilation amplitude is found to be very sizable in the $SP$ sector with $|A/T|_{SP}\sim 1/2$, contrary to its suppression in the $PP$ sector with $|A/T|_{PP}\sim 0.18$.

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arXiv2021

Direct CP violation in charmed meson decays within the standard model

Direct CP violation in two-body $D\to PP$ and $D\to V\!P$ decays is studied within the framework of the topological amplitude approach for tree amplitudes and the QCD factorization approach for penguin amplitudes. It is the interference between tree and long-distance penguin and penguin-exchange amplitudes that pushes CP asymmetry difference between $D^0\to K^+K^-$ and $π^+π^-$ modes up to the per mille level. Using the same mechanism, we find that CP asymmetry can also occur at the $10^{-3}$ level in many of the $D\to V\!P$ channels or otherwise be negligibly small. There are six golden modes which have sufficiently large branching fractions and direct CP violation at the per mille level. In particular, the direct CP asymmetry difference between $D^0\to K^+K^{*-}$ and $π^+ρ^-$ is predicted to be $(-1.61\pm0.33)\times 10^{-3}$, very similar to the counterpart in the $P\!P$ sector. The LHCb's observation of CP asymmetry difference can be explained within the standard model without the need of new physics. The key lies in the long-distance penguin topology (penguin and penguin-exchange) arising from final-state rescattering.

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arXiv2021

The strangest lifetime: A bizarre story of $τ(Ω_c^0)$

For a long time it has been established both experimentally and theoretically that $Ω_c^0$ is shortest-lived among the four singly charmed baryons which decay weakly. The situation was dramatically changed in 2018 when LHCb reported a new measurement of the $Ω_c^0$ lifetime using semileptonic $b$-hadron decays. The value is nearly four times larger than the previous world average of $τ(Ω_c^0)$ and it is confirmed by the most recent LHCb measurement with the prompt production. In this viewpoint article, we review the status and point out that heavy quark expansion (HQE) fails to apply to $Ω_c^0$ to the order of $1/m_c^4$. By demanding a sensible HQE for $Ω_c^0$ will lead to a lifetime of $Ω_c^0$ longer than $Λ_c^+$.

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arXiv2021

CP violation in quasi-two-body $D\to VP$ decays and three-body $D$ decays mediated by vector resonances

We re-examine direct CP violation in the quasi-two-body $D\to V\!P$ decays and study CP asymmetries in three-body $D$ decays proceeding through intermediate vector resonances within the framework of the topological amplitude approach for tree amplitudes and the QCD factorization approach for penguin amplitudes. Using the same mechanism of incorporating long-distance penguin-exchange amplitude induced from final-state rescattering that nicely accounts for the CP asymmetry difference between $D^0\to K^+K^-$ and $π^+π^-$ modes, we find that CP asymmetry can also occur at the per mille level in many of the $D\to V\!P$ channels or otherwise be negligibly small. We point out six golden modes which have sufficiently large branching fractions and direct CP violation of order $10^{-3}$. In particular, the direct CP asymmetry difference $Δa_{CP}^{V\!P}$ between $D^0\to K^+K^{*-}$ and $π^+ρ^-$ is predicted to be $(-1.61\pm0.33)\times 10^{-3}$, very similar to the counterpart in the $P\!P$ sector. Besides, we find a positive and large CP asymmetry of order $10^{-3}$ in $D^0\to K_S K^{*0}$, an example of the asymmetry induced at the tree level. We take into account the flavor-singlet QCD-penguin contributions to calculate their effects on the modes such as $D\toπϕ$ and $D\to ηϕ$. We compare our results with the other approach in detail. For three-body $D$ decays, we perform the Dalitz plot analysis of those decays mediated by several vector resonances with the same mass but different electric charges. Local CP asymmetry varies in magnitude and sign from region to region and can reach the percent level in certain local regions of phase space due to interference.

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arXiv2021

Finite-Width Effects in Three-Body B Decays

It is customary to apply the so-called narrow width approximation $Γ(B\to RP_3\to P_1P_2P_3)=Γ(B\to RP_3)Br(R\to P_1P_2)$ to extract the branching fraction of the quasi-two-body decay $B\to RP_3$, with $R$ and $P_3$ being an intermediate resonant state and a pseudoscalar meson, respectively. However, the above factorization is valid only in the zero width limit. We consider a correction parameter $η_R$ from finite width effects. Our main results are: (i) We present a general framework for computing $η_R$ and show that it can be expressed in terms of the normalized differential rate and determined by its value at the resonance. (ii) We introduce a form factor $F(s_{12},m_R)$ for the strong coupling involved in the $R(m_{12})\to P_1P_2$ decay when $m_{12}$ is away from $m_R$. We find that off-shell effects are small in vector meson productions, but prominent in the $K_2^*(1430)$, $σ/f_0(500)$ and $K_0^*(1430)$ resonances. (iii) We evaluate $η_R$ in the theoretical framework of QCD factorization (QCDF) and in the experimental parameterization (EXPP) for three-body decay amplitudes. In general, $η_R^{\rm QCDF}$ and $η_R^{\rm EXPP}$ are similar for vector mesons, but different for tensor and scalar resonances. A study of the differential rates enables us to understand the origin of their differences. (iv) Finite-width corrections to $Br(B^-\to RP)_{\rm NWA}$ obtained in the narrow width approximation are generally small, less than 10\%, but they are prominent in $B^-\toσ/f_0(500)π^-$ and $B^-\to \overline K_0^{*0}(1430)π^-$ decays. The EXPP of the normalized differential rates should be contrasted with the theoretical predictions from QCDF calculation as the latter properly takes into account the energy dependence in weak decay amplitudes.

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arXiv2020

Width effects in resonant three-body decays: $B$ decay as an example

For three-body hadron decays mediated by intermediate resonances with large widths, we show how to properly extract the quasi-two-body decay rates for a meaningful comparison with the corresponding theoretical estimates, using several $B$ decays as explicit examples. We compute the correction factor from finite width effects in the QCD factorization approach, and make a comparison with that using the experimental parameterization in which the momentum dependence in the weak dynamics is absent. Although the difference is generally less than $10\%$ for tensor and vector resonances, it can be as large as $(25-40)\%$ for scalar resonances. Our finding can in fact be applied to general quasi-two-body decays.

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arXiv2020

Branching Fractions and CP Violation in $B^-\to K^+K^-π^-$ and $B^-\to π^+π^-π^-$ Decays

We present in this work a study of tree-dominated charmless three-body decays of $B$ mesons, $B^-\to K^+K^-π^-$ and $B^-\toπ^+π^-π^-$, within the factorization approach. The main results are: (i) There are two distinct sources of nonresonant contributions: one arises from the $b\to u$ tree transition and the other from the nonresonant matrix element of scalar densities $\langle M_1M_2|\bar q_1 q_2|0\rangle^{\rm NR}$. It turns out that even for tree-dominated three-body decays, dominant nonresonant contributions originate from the penguin diagram rather than from the $b\to u$ tree process, as implied by the large nonresonant component observed recently in the $π^- K^+$ system which accounts for one third of the $B^-\to K^+K^-π^-$ rate. (ii) The calculated branching fraction of $B^-\to f_2(1270)π^-\to K^+K^-π^-$ is smaller than the LHCb by a factor of $\sim 7$ in its central value, but the predicted $\B(B^-\to f_2(1270)π^-\toπ^+π^-π^-)$ is consistent with the data. Branching fractions of $B^-\to f_2(1270)π^-$ extracted from the LHCb measurements of these two processes also differ by a factor of seven! Therefore, it is likely that the $f_2(1270)$ contribution to $B^-\to K^+K^-π^-$ is largely overestimated experimentally. Including $1/m_b$ power corrections from penguin annihilation inferred from QCD factorization (QCDF), a sizable CP asymmetry of 32\% in the $f_2(1270)$ component agrees with experiment. (iii) A fraction of 5\% for the $ρ(1450)$ component in $B^-\toπ^+π^-π^-$ is in accordance with the theoretical expectation. However, a large fraction of 30\% in $B^-\to K^+K^-π^-$ is entirely unexpected. This issue needs to be clarified in the future.

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arXiv2020

CP Violation in $B^\pm\to ρ^0π^\pm$ and $B^\pm\to σπ^\pm$ Decays

The decay amplitude of $B^+\to π^+π^-π^+$ in the Dalitz plot has been analyzed by the LHCb using three different approaches for the $S$-wave component. It was found that the mode with $σ$ (or $f_0(500)$) exhibited a CP asymmetry of 15\% in the isobar model, whereas the $f_2(1270)$ mode had a 40\% asymmetry. On the contrary, CP asymmetry for the dominant quasi-two-body decay $B^-\toρ^0π^-$ was found to be consistent with zero in all three approaches, while all the existing theoretical predictions lead to a negative CP asymmetry ranging from $-7\%$ to $-45\%$. We show that the nearly vanishing CP violation in $B^-\toρ^0π^-$ is understandable in the framework of QCD factorization (QCDF). It arises from the $1/m_b$ power corrections to the penguin amplitudes due to penguin annihilations and to the color-suppressed tree amplitude due to hard spectator interactions. Penguin annihilation and hard spectator interactions contribute destructively to $A_{CP}(B^-\toρ^0π^-)$ to render it consistent with zero. The branching fraction and CP asymmetry in $B^-\toσ/f_0(500)π^-$ are investigated in QCDF with results in agreement with experiment.

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arXiv2020

Two-body weak decays of doubly charmed baryons

The hadronic two-body weak decays of the doubly charmed baryons $Ξ_{cc}^{++}, Ξ_{cc}^+$ and $Ω_{cc}^+$ are studied in this work. To estimate the nonfactorizable contributions, we work in the pole model for the $P$-wave amplitudes and current algebra for $S$-wave ones. For the $Ξ_{cc}^{++}\to Ξ_c^+π^+$ mode, we find a large destructive interference between factorizable and nonfactorizable contributions for both $S$- and $P$-wave amplitudes. Our prediction of $\sim 0.70\%$ for its branching fraction is smaller than the earlier estimates in which nonfactorizable effects were not considered, but agrees nicely with the result based on an entirely different approach, namely, the covariant confined quark model. On the contrary, a large constructive interference was found in the $P$-wave amplitude by Dhir and Sharma, leading to a branching fraction of order $(7-16)\%$. Using the current results for the absolute branching fractions of $(Λ_c^+,Ξ_c^+)\to p K^-π^+$ and the LHCb measurement of $Ξ_{cc}^{++}\toΞ_c^+π^+$ relative to $Ξ_{cc}^{++}\toΛ_c^+ K^- π^+π^+$, we obtain $\B(Ξ_{cc}^{++}\toΞ_c^+π^+)_{\rm expt}\approx (1.83\pm1.01)\%$ after employing the latest prediction of $\B(Ξ_{cc}^{++}\toΣ_c^{++}\overline{K}^{*0})$. Our prediction of $\mathcal{B}(Ξ_{cc}^{++}\toΞ_c^+π^+)\approx 0.7\%$ is thus consistent with the experimental value but in the lower end. It is important to pin down the branching fraction of this mode in future study. Factorizable and nonfactorizable $S$-wave amplitudes interfere constructively in $Ξ_{cc}^+\toΞ_c^0π^+$. Its large branching fraction of order 4\% may enable experimentalists to search for the $Ξ_{cc}^+$ through this mode. That is, the $Ξ_{cc}^+$ is reconstructed through the $Ξ_{cc}^+\toΞ_c^0π^+$ followed by the decay chain $Ξ_c^0\to Ξ^-π^+\to pπ^-π^-π^+$.

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arXiv2020

Two-body hadronic weak decays of antitriplet charmed baryons

We study Cabibbo-favored (CF) and singly Cabibbo-suppressed (SCS) two-body hadronic weak decays of the antitriplet charmed baryons $Λ_c^+$, $Ξ_c^0$ and $Ξ_c^+$ with more focus on the last two. Both factorizable and nonfactorizable contributions are considered in the topologic diagram approach. The estimation of nonfactorizable contributions from $W$-exchange and inner $W$-emission diagrams relies on the pole model and current algebra. The non-perturbative parameters in both factorizable and nonfactorizable parts are calculated in the MIT bag model. Branching fractions and up-down decay asymmetries for all the CF and SCS decays of antitriplet charmed baryons are presented. The prediction of $\mathcal{B}(Ξ_c^+\to Ξ^0π^+ )$ agrees well with the measurements inferred from Belle and CLEO, while the calculated ${\cal B}(Ξ_c^0\to Ξ^-π^+)$ is too large compared to the recent Belle measurement. We conclude that these two $Ξ_c\toΞπ^+$ modes cannot be simultaneously explained within the current-algebra framework for $S$-wave amplitudes. This issue needs to be resolved in future study. The long-standing puzzle with the branching fraction and decay asymmetry of $Λ_c^+\toΞ^0 K^+$ is resolved by noting that only type-II $W$-exchange diagram will contribute to this mode. We find that not only the calculated rate agrees with experiment but also the predicted decay asymmetry is consistent with the SU(3)-flavor symmetry approach in sign and magnitude. Likewise, the CF mode $Ξ_c^0\to Σ^+K^-$ and the SCS decays $Ξ_c^0\to pK^-,Σ^+π^-$ proceed only through type-II $W$-exchange. They are predicted to have large and {\it positive} decay asymmetries. These features can be tested in the near future.

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arXiv2019

Revisiting CP violation in $D\to P\!P$ and $V\!P$ decays

Direct CP violation in the hadronic charm decays provides a good testing ground for the Kobayashi-Maskawa mechanism in the Standard Model. Any significant deviations from the expectation would be indirect evidence of physics beyond the Standard Model. In view of improved measurements from LHCb and BESIII experiments, we re-analyze the Cabibbo-favored $D \to P\!P$ and $V\!P$ decays in the topological diagram approach. By assuming certain SU(3)-breaking effects in the tree-type amplitudes, we make predictions for both branching fractions and CP asymmetries of the singly Cabibbo-suppressed decay modes. While the color-allowed and -suppressed amplitudes are preferred to scale by the factor dictated by factorization in the $P\!P$ modes, no such scaling is required in the $V\!P$ modes. The $W$-exchange amplitudes are found to change by 10\% to 50\% and depend on whether $d\overline{d}$ or $s\overline{s}$ pair directly emerges from $W$-exchange. The predictions of branching fractions are generally improved after these SU(3) symmetry breaking effects are taken into account. We show in detail how the tree-type, QCD-penguin, and weak penguin-annihilation diagrams contribute and modify CP asymmetry predictions. Future measurements of sufficiently many direct CP asymmetries will be very useful in removing a discrete ambiguity in the strong phases as well as discriminating among different theory approaches. In particular, we predict $a_{CP}(K^+K^-)-a_{CP}(π^+π^-) = (-1.14 \pm 0.26) \times 10^{-3}$ or $(-1.25 \pm 0.25) \times 10^{-3}$, consistent with the latest data, and $a_{CP}(K^+K^{*-})-a_{CP}(π^+ρ^-) = (-1.52 \pm 0.43) \times 10^{-3}$, an attractive and measurable observable in the near future. Moreover, we observe that such CP asymmetry differences are dominated by long-distance penguin-exchange through final-state rescattering.

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arXiv2019

Lifetimes of Doubly Heavy Baryons ${\cal B}_{bb}$ and ${\cal B}_{bc}$

Lifetimes of the doubly heavy baryons ${\cal B}_{bb}$ and ${\cal B}_{bc}$ are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from the spectator effects such as $W$-exchange and Pauli interference. For doubly bottom baryons, the lifetime pattern is $τ(Ω_{bb}^-)\sim τ(Ξ_{bb}^{-})>τ(Ξ_{bb}^0)$. The $Ξ_{bb}^{0}$ baryon is shortest-lived owing to the $W$-exchange contribution, while $Ξ_{bb}^{-}$ and $Ω_{bb}^{-}$ have similar lifetimes as they both receive contributions from destructive Pauli interference. We find the lifetime ratio $τ(Ξ_{bb}^{-})/τ(Ξ_{bb}^0)=1.26$\,. The large $W$-exchange contribution to $Ξ_{bc}^0$ through the subprocess $cd\to us\to cd$ and the sizable destructive Pauli interference contribution to $Ξ_{bc}^+$ imply a substantial lifetime difference between $Ξ_{bc}^+$ and $Ξ_{bc}^0$. In the presence of subleading $1/m_c$ and $1/m_b$ corrections to the spectator effects, we find that $τ(Ω_{bc}^0)$ becomes longest-lived. This is because $Γ^{\rm int}_+$ and $Γ^{\rm semi}$ for $Ω_{bc}^0$ are subject to large cancellation between dimension-6 and -7 operators. This implies that the subleading corrections are too large to justify the validity of the HQE. Demanding that $Γ^{cs}_{\rm int+}(Ω_{bc}^0)$, $Γ^{{\rm SL},cs}_{\rm int}(Ω_{bc}^0)$ be positive and $Γ^{cu}_{\rm int-}(Ξ^+_{bc})$ be negative, we conjecture that $1.68\times 10^{-13}s<τ(Ω_{bc}^0)< 3.70\times 10^{-13}s$ , $4.09\times 10^{-13}s<τ(Ξ_{bc}^+)< 6.07\times 10^{-13}s$ and $0.93\times 10^{-13}s<τ(Ξ_{bc}^0)< 1.18\times 10^{-13}s$. Hence, the lifetime hierarchy of ${\cal B}_{bc}$ baryons is expected to be the pattern $τ(Ξ_{bc}^{+})>τ(Ω_{bc}^0)>τ(Ξ_{bc}^0)$.

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arXiv2018

Lifetimes of Doubly Charmed Baryons

The lifetimes of doubly charmed hadrons are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from spectator effects such as $W$-exchange and Pauli interference. The $Ξ_{cc}^{++}$ baryon is longest-lived in the doubly charmed baryon system owing to the destructive Pauli interference absent in the $Ξ_{cc}^+$ and $Ω_{cc}^+$. In the presence of dimension-7 contributions, its lifetime is reduced from $\sim5.2\times 10^{-13}s$ to $\sim3.0\times 10^{-13}s$. The $Ξ_{cc}^{+}$ baryon has the shortest lifetime of order $0.45\times 10^{-13}s$ due to a large contribution from the $W$-exchange box diagram. It is difficult to make a precise quantitative statement on the lifetime of $Ω_{cc}^+$. Contrary to $Ξ_{cc}$ baryons, $τ(Ω_{cc}^+)$ becomes longer in the presence of dimension-7 effects and the Pauli interference $Γ^{\rm int}_+$ even becomes negative. This implies that the subleading corrections are too large to justify the validity of the HQE. Demanding the rate $Γ^{\rm int}_+$ to be positive for a sensible HQE, we conjecture that the $Ω_c^0$ lifetime lies in the range of $(0.75\sim 1.80)\times 10^{-13}s$. The lifetime hierarchy pattern is $τ(Ξ_{cc}^{++})>τ(Ω_{cc}^+)>τ(Ξ_{cc}^+)$ and the lifetime ratio $τ(Ξ_{cc}^{++})/τ(Ξ_{cc}^+)$ is predicted to be of order 6.7.

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arXiv2018

Phenomenological Study of Heavy Hadron Lifetimes

The lifetimes of bottom and charmed hadrons are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from the spectator effects such as weak $W$-annihilation and Pauli interference. Spectator effects originating from dimension-7 four-quark operators are derived. Hadronic matrix elements of four-quark operators are parameterized in a model-independent way. Using the dimension-6 bag parameters recently determined from HQET sum rules and the vacuum insertion approximation for meson matrix elements of dimension-7 operators, the calculated $B$ meson lifetime ratios $τ(B^+)/τ(B^0_d)=1.074$ and $τ(B^0_s)/τ(B^0_d)=0.996$ are in excellent agreement with experiment. Likewise, based on the quark model evaluation of baryon matrix elements, the resulting baryon lifetime ratios $τ(Ξ_b^-)/τ(Λ_b^0)$, $τ(Ξ_b^-)/τ(Ξ_b^0)$, $τ(Ω_b^-)/τ(Ξ_b^-)$ and the $Λ_b-B^0$ lifetime ratio $τ(Λ_b^0)/τ(B^0_d)=0.955$ also agree well with the data. Contrary to the bottom hadron sector where the HQE in $1/m_b$ works well, the HQE to $1/m_c^3$ fails to give a satisfactory description of the lifetimes of both charmed mesons and charmed baryons. This calls for the subleading $1/m_Q$ corrections to spectator effects. The relevant dimension-7 spectator effects are in the right direction for explaining the large lifetime ratio of $τ(Ξ_c^+)/τ(Λ_c^+)$.

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arXiv2018

Singly Cabibbo-suppressed hadronic decays of $Λ_c^+$

We study singly Cabibbo-suppressed two-body hadronic decays of the charmed baryon $Λ_c^+$, namely, $Λ_c^+\to ΛK^+, pπ^0, pη, nπ^+,Σ^0K^+,Σ^+ K^0$. We use the measured rate of $Λ_c^+\to pϕ$ to fix the effective Wilson coefficient $a_2$ for naive color-suppressed modes and the effective number of color $N_c^{\rm eff}$. We rely on the current-algebra approach to evaluate $W$-exchange and nonfactorizable internal $W$-emission amplitudes, that is, the commutator terms for the $S$-wave and the pole terms for the $P$-wave. Our prediction for $Λ_c^+\to pη$ is in excellent agreement with the BESIII measurement. The $pη$ ($pπ^0$) mode has a large (small) rate because of a large constructive (destructive) interference between the factorizable and nonfactorizable amplitudes for both $S$- and $P$-waves. Some of the SU(3) relations such as $M(Λ_c^+\to nπ^+)=\sqrt{2}M(Λ_c^+\to pπ^0)$ derived under the assumption of sextet dominance are not valid for decays with factorizable terms. Our calculation indicates that the branching fraction of $Λ_c^+\to nπ^+$ is about 3.5 times larger than that of $Λ_c^+\to pπ^0$. Decay asymmetries are found to be negative for all singly Cabibbo-suppressed modes and range from $-0.56$ to $-0.96$.

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arXiv2018

The semileptonic baryonic decay $D_s^+\to p\bar p e^+ ν_e$

The decay $D_s^+\to p \bar p e^+ν_e$ with a proton-antiproton pair in the final state is unique in the sense that it is the only semileptonic baryonic decay which is physically allowed in the charmed meson sector. Its measurement will test our basic knowledge on semileptonic $D_s^+$ decays and the low-energy $p\bar p$ interactions. Taking into account the major intermediate state contributions from $η, η', f_0(980)$ and $X(1835)$, we find that its branching fraction is at the level of $10^{-9} \sim 10^{-8}$. The location and the nature of $X(1835)$ state are crucial for the precise determination of the branching fraction. We wish to trigger a new round of a careful study with the upcoming more data in BESIII as well as the future super tau-charm factory.

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arXiv2017

Prediction of the $CP$ asymmetry $C_{00}$ in $B^0 \to D^0\overline{D^0}$ decay

Of all $B \to D \overline{D}$ decays, the $B^0 \to D^0 \overline{D^0}$ decay has the smallest observed branching ratio as it takes place primarily via the suppressed $W$-exchange diagram. The $CP$ asymmetry for this mode is yet to be measured experimentally. By exploiting the relationship among the decay amplitudes of $B \to D\overline{D}$ decays (using isospin and topological amplitudes) we are able to relate the $CP$ asymmetries and branching ratios by a simple expression. This enables us to predict the $CP$ asymmetry $C_{00}$ in $B^0 \to D^0 \overline{D^0}$. While the predicted central values of $C_{00}$ are outside the physically allowed region, they are currently associated with large uncertainties owing to the large errors in the measurements of the $B^0 \to D^0 \overline{D^0}$ branching ratio ($B_{00}$), the other $CP$ asymmetries $C_{+-}$ (of $B^0 \to D^+ D^-$) and $A_{\text{CP}}$ (of $B^+ \to D^+ \overline{D^0}$). With a precise determination of $B_{00}$, $C_{+-}$ and $A_{\text{CP}}$, one can use our analytical result to predict $C_{00}$ with a reduced error and compare it with the experimental measurement when it becomes available. The correlation between $B_{00}$ and $C_{00}$ is an interesting aspect that can be probed in ongoing and future particle physics experiments such as LHCb and Belle II.

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arXiv2017

Branching fractions of semileptonic $D$ and $D_s$ decays from the covariant light-front quark model

Based on the predictions of the relevant form factors from the covariant light-front quark model, we show the branching fractions for the $D (D_s) \to (P,\,S,\,V,\,A)\,\ellν_\ell$ ($\ell=e$ or $μ$) decays, where $P$ denotes the pseudoscalar meson, $S$ the scalar meson with a mass above 1 GeV, $V$ the vector meson and $A$ the axial-vector one. Comparison with the available experimental results are made, and we find an excellent agreement. The predictions for other decay modes can be tested in a charm factory, e.g., the BESIII detector. The future measurements will definitely further enrich our knowledge on the hadronic transition form factor as well as the inner structure of the even-parity mesons ($S$ and $A$).

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