arXiv subjects

Cai-Dian Lu

Publications and source records attributed to Cai-Dian Lu.

At least 37 records · Page 2Linked to original sources

arXiv2015

Improved Estimates of The $B_{(s)}\to V V$ Decays in Perturbative QCD Approach

We reexamine the branching ratios, $CP$-asymmetries, and other observables in a large number of $B_q\to VV(q=u,d,s)$ decays in the perturbative QCD (PQCD) approach, where $V$ denotes a light vector meson $(ρ, K^*, ω, ϕ)$. The essential difference between this work and the earlier similar works is of parametric origin and in the estimates of the power corrections related to the ratio $r_i^2=m_{V_i}^2/m_B^2(i=2,3)$ ($m_V$ and $m_B$ denote the masses of the vector and $B$ meson, respectively). In particular, we use up-to-date distribution amplitudes for the final state mesons and keep the terms proportional to the ratio $r_i^2$ in our calculations. Our updated calculations are in agreement with the experimental data, except for a limited number of decays which we discuss. We emphasize that the penguin annihilation and the hard-scattering emission contributions are essential to understand the polarization anomaly, such as in the $B\to ϕK^*$ and $B_s \to ϕϕ$ decay modes. We also compare our results with those obtained in the QCD factorization (QCDF) approach and comment on the similarities and differences, which can be used to discriminate between these approaches in future experiments.

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arXiv2014

The study of the nonleptonic two body B decays involving a light tensor meson in final states

The nonleptonic two body $B_{u,d,s,c}$ decays involving a light tensor meson in final states are studied in the perturbative QCD approach based on $k_T$ factorization. The decay modes with a tensor meson emitted, are prohibited in naive factorization, since the emission diagram with a tensor meson produced from vacuum is vanished. While contributions from the so-called hard scattering emission diagrams and annihilation type diagrams are important and calculable in the perturbative QCD approach. The branching rations of most decays are in the range of $10^{-4}$ to $10^{-8}$, which are bigger by 1 or 2 orders of magnitude than the predictions given by naive factorization, but consistent with the predictions from QCD factorization and the recent experimental measurements. We also give the predictions for the direct $CP$ asymmetries, some of which are large enough for the future experiments to measure. We also find that, even with a small mixing angle, the mixing between $f_2$ and $f_2^{\prime}$ can bring remarkable changes to both branching ratios and the direct $CP$ asymmetries for some decays involving $f_2^{(\prime)}$ mesons. For decays with a vector meson and a tensor meson in final states, we predict a large percentage of transverse polarization contributions due to the contributions of the orbital angular momentum of the tensor mesons.

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arXiv2013

Study the Forward-Backward Asymmetry of the Top Quark Production in the Randall-Sundrum Model with an Extension of Strong Interaction

The large forward-backward asymmetry of the top quark pair production measured by the hadron colliders shed light on new physics signals beyond the Standard Model. In the Randall-Sundrum model with an additional SU(3) group in the strong sector, we compare the total cross section and forward-backward asymmetry of the top quark pair production with the newest data obtained by the CDF and the D0 collaborations. Our numerical analysis shows that the parameter $c_q \gtrsim 0.5$, $c_t \sim -0.6\sim-0.8$, $\tanϕ\gtrsim 20$ or $\tanϕ\leq 1/20$ and the first excitation of axial gluon with a mass about $5 \thicksim 6 \mathrm{TeV}$ can accommodate this large anomaly without violating other experimental constraints.

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arXiv2013

Time-dependent CP-violations of B(Bs) decays in the perturbative QCD approach

We study the decay modes of B_{s}^{0}(\bar{B}_{s}^{0})-->D_{s}^{\pm} K^{\mp}, B_{s}^{0}(\bar{B}_{s}^{0})-->D^{\pm} π^{\mp} and B^{0}(\bar{B}^{0})-->D^{\pm} π^{\mp} in the perterbative QCD approach based on k_T factorization, including the branching ratios and CP violation parameters which provide a clear way to extract the Cabibbo-Kobayashi-Maskawa angle γ. Our results of branching ratios of B_{s}^{0}(\bar{B}_{s}^{0})-->D_{s}^{\pm} K^{\mp} and B^{0}(\bar{B}^{0})--> D^{\pm} π^{\mp} and the CP asymmetry of B^{0}(\bar{B}^{0})--> D^{\pm} π^{\mp} agree well with the experimental data. We also give the predictions of the other observables, which provide some guidance for experiments in the future, especially for LHCb experiment.

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arXiv2012

Recent theoretical improvement of hadronic $B_s$ decays

In this mini-review, we show that a lot of theoretical efforts have been made for the theoretical study of two body hadronic $B_{(s)}$ and $B_c$ decays. In addition to many next-to-leading order or even next-to-next-to leading order $α_s$ corrections made, we also study many of the previously unknown next-to-leading order power corrections. While the former corrections are theoretically solid, the latter corrections are phenomenologically more important. In the QCD factorization approach based on collinear factorization, there is difficulty to deal with the power correction diagrams due to the endpoint singularity. Thus many of these analysis use phenomenological method. In the perturbative QCD approach based on $k_T$ factorization, the endpoint singularity is killed by including the quark transverse momentum. Therefore we can calculate the annihilation type diagrams quantitatively, which give the right sign for the direct CP asymmetry parameters. More and more $B_{(s)}$ decays channels, especially the pure annihilation type decays have been measured by the recent experiments to confirm our theoretical predictions. More channels are predicted for future experiments, such as the charmless and charmed $B_s$ and $B_c$ hadronic decays and the decays involving a scalar, axial vector, even a tensor meson in the final states.

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arXiv2012

Branching ratios and direct CP asymmetries in $D\to PP$ decays

We propose a theoretical framework for analyzing two-body nonleptonic $D$ meson decays, based on the factorization of short-distance (long-distance) dynamics into Wilson coefficients (hadronic matrix elements of four-fermion operators). The parametrization of hadronic matrix elements in terms of several nonperturbative quantities is demonstrated for the $D\to PP$ decays, $P$ denoting a pseudoscalar meson. We consider the evolution of Wilson coefficients with energy release in individual decay modes, and the Glauber strong phase associated with the pion in nonfactorizable annihilation amplitudes, that is attributed to the unique role of the pion as a Nambu-Goldstone boson and a quark-anti-quark bound state simultaneously. The above inputs improve the global fit to the branching ratios involving the $η'$ meson, and resolves the long-standing puzzle from the $D^0\toπ^+π^-$ and $D^0\to K^+K^-$ branching ratios, respectively. Combining short-distance dynamics associated with penguin operators and the hadronic parameters determined from the global fit to branching ratios, we predict direct CP asymmetries, to which the quark loops and the scalar penguin annihilation give dominant contributions. In particular, we predict $ΔA_{\rm CP}\equiv A_{\rm CP}(K^+K^-)-A_{\rm CP}(π^+π^-)=-1.00\times 10^{-3}$, lower than the LHCb and CDF data.

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arXiv2012

The two-body B_c {\to} D^{()}_{(s)}P, D^{()}_{(s)}V decays in the Perturbative QCD Approach

We make a systematic investigation on the two-body nonleptonic decays B_c {\to} D^{(*)}_{(s)}P, D^{(*)}_{(s)}V, by employing the perturbative QCD approach based on k_T factorization, where P and V denote any light pseudoscalar meson and vector meson, respectively. We predict the branching ratios and direct CP-asymmetries of these B_c decays and also the transverse polarization fractions of B_c {\to} D^{*}_{(s)}V decays. It is found that the non-factorizable emission diagrams and annihilation type diagrams have remarkable effects on the physical observables in many channels, especially the color-suppressed and annihilation-dominant decay modes. A possible large direct CP-violation is predicted in some channels; and a large transverse polarization contribution that can reach 50% ~ 70% is predicted in some of the Bc {\to} D^{*}_{(s)}V decays.

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arXiv2012

The double charm decays of $B_c$ Meson in the Perturbative QCD Approach

We make a systematic investigation on the double charm decays of $B_c$ meson, by employing the perturbative QCD approach based on $k_T$ factorization. It is found that the non-factorizable emission diagrams are not negligible in these channels. We predict the branching ratios of these $B_c$ decays and also the transverse polarization fractions of $B_c\rightarrow D_{(s)}^{*+}\bar D^{*0}, D_{(s)}^{*+}D^{*0}$ decays, % where V denote the vector $D^*_{(s)}$ meson. We find that the magnitudes of the branching ratios of the decays $B_c\rightarrow D_s\bar{D}^0$ and $B_c\rightarrow D_sD^0$ are very close to each other, which are well suited to extract the Cabibbo-Kobayashi-Maskawa angle $γ$ through the amplitude relations. In addition, a large transverse polarization contribution that can reach $50%\sim 60%$ is predicted in some of the $B_c$ meson decay to two vector charmed mesons.

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arXiv2012

Charmed B(B_{s}) decays involving a light tensor meson in PQCD approach

We study the $B(B_{s})\rightarrow D_{(s)}(\bar{D}_{(s)})\,T$ and $D_{(s)}^{\ast}(\bar{D}_{(s)}^{*})\,T$ decays in perturbative QCD approach, where T denotes a light tensor meson. In addition to the branching ratios, we also give predictions to the polarization fractions for the $D^{*}_{(s)}(\bar{D}_{(s)}^{*})T$ decays. For those decays with a tensor meson emitted, the factorizable emission diagrams do not contribute because of lorentz covariance considerations. In order to give the predictions to these decay channels, it is necessary to go beyond the naive factorization to calculate the nonfactorizable and annihilation diagrams.

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arXiv2012

The $B_c\rightarrow D^{(*)}T$ decays in perturbative QCD approach

In this work, we investigate those $B_{c}\rightarrow D^{(*)}T$ decays in perturbative QCD approach, based on $k_T$ factorization, where T denotes a light tensor meson. For all decays considered in this work, there are no contributions from factorizable emission diagrams because the emitted meson is the tensor meson. We find that the annihilation amplitudes are dominant in these decays due to the large Cabibbo-Kobayashi-Maskawa elements, which are only calculable in the pQCD approach. The numerical results show that the predictions for the branching ratios of most decays are in the order of $10^{-6}$ or even bigger, which can be observed in the ongoing experiments. We also predict large percentage of transverse polarizations in those W annihilation diagram dominant $B_{c} \rightarrow D^{*}T$ decay channels.

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arXiv2012

Forward-backward asymmetry of $B\to K_J l^+l^-$ decays in SM and new physics models

We report on our studies of $B\to K_Jl^+l^-$ in the standard model and several new physics variations, with $K_J$ denoting a kaonic resoanance. In terms of helicity amplitudes, we derive a compact form for the full angular distributions, and use them to calculate the branching ratios, forward-backward asymmetries and polarizations. We have updated the constraints on effective Wilson coefficients and/or free parameters in these new physics scenarios by making use of the $B\to K^*l^+l^-$ and $b\to s l^+l^-$ experimental data. Their impact on $B\to K_J^*l^+l^-$ is subsequently explored and in particular the zero-crossing point for forward-backward asymmetry in new physics scenarios can sizably deviate from the standard model.

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arXiv2012

The $B(B_{s})\rightarrow D_{(s)}(\bar{D}_{(s)}) T$ and $D_{(s)}^{}(\bar{D}_{(s)}^{})T$ decays in perturbative QCD approach

In perturbative QCD approach, we investigate the $B(B_{s})\rightarrow D_{(s)}(\bar{D}_{(s)})\,T$ and $D_{(s)}^{*}(\bar{D}_{(s)}^{*})\,T$ decays, which include the Cabibbo-Kobayashi-Maskawa (CKM) favored decays and the Cabibbo-Kobayashi-Maskawa-suppressed decays, where T denotes a light tensor meson. From our calculation, we find that the nonfactorizable emission diagrams and the annihilation type diagrams are important, especially for those color suppressed channels. For those decays with a tensor meson emitted, the factorizable emission diagrams vanish owing to the fact that a tensor meson can not be produced through the local (V-A) or tensor current. The numerical results show that the predictions for the branching ratios of considered charmed B decays are in the range of $10^{-4}$ to $10^{-6}$ for those CKM-favored decays (governed by $|V_{cb}|$) and in the range of $10^{-5}$ to $10^{-8}$ for those CKM-suppressed decays (governed by $|V_{ub}|$). We also predict large transverse polarization contributions in many of the $B(B_{s}) \rightarrow D_{(s)}^{\ast}(\bar{D}_{(s)}^{*})T$ decay channels.

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arXiv2012

The pure annihilation type decays $B^0\rightarrow D_{s}^{-}K_{2}^{*+}$ and $B_{s}\rightarrow \bar{D}a_{2}$ in perturbative QCD approach

We calculate the branching ratios of pure annihilation type decays $B^0\rightarrow D_{s}^{-}K_{2}^{*+}$ and $B_s\rightarrow \bar{D}a_{2}$ using the perturbative QCD approach based on $k_T$ factorization. The branching ratios are predicted to be $(60.6_{-16.5\,-10.4\,-2.1}^{+17.3\,+4.3\,+3.2}) \times 10^{-6}$ for $B^0\rightarrow D_{s}^{-}K_{2}^{*+}$, $(1.1_{-0.4\,-0.2\,-0.1}^{+0.4\,+0.1\,+0.1})\times 10^{-6}$ for $B_s\rightarrow \bar{D}a_{2}^{0}$ and $(2.3_{-0.8\,-0.4\,-0.1}^{+0.8\,+0.2\,+0.1})\times 10^{-6}$ for $B_{s}\rightarrow D^{-}a_{2}^{+}$. They are large enough to be measured in the ongoing experiment. Due to the shortage of contributions from penguin operators, there are no direct CP asymmetries for these decays in the standard model. We also derive simple relations among these decay channels to reduce theoretical uncertainties for the experiments to test the accuracy of theory and search of new physics signal.

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arXiv2012

Nonleptonic two-body charmless B decays involving a tensor meson in the Perturbative QCD Approach

Two-body charmless hadronic B decays involving a light tensor meson in the final states are studied in the perturbative QCD approach based on $k_T$ factorization. From our calculations, we find that the decay branching ratios for color allowed tree-dominated decays $B\to a_{2}^{0}π^{+}$ and $B\to a_{2}^{-}π^{+}$ modes are of order $10^{-6}$ and $10^{-5}$, respectively. While other color suppressed tree-dominated decays have very small branching ratios. In general, the branching ratios of most decays are in the range of $10^{-5}$ to $10^{-8}$, which are bigger by one or two orders of magnitude than those predictions obtained in Isgur-Scora-Grinstein-Wise II model and in the covariant light-front approach, but consistent with the recent experimental measurements and the QCD factorization calculations. Since the decays with a tensor meson emitted from vacuum are prohibited in naive factorization, the contributions of nonfactorizable and annihilation diagrams are very important to these decays, which are calculable in our perturbative QCD approach. We also give predictions to the direct CP asymmetries, some of which are large enough for the future experiments to measure. Because we considered the mixing between $f_{2}$ and $f_{2}'$, the decay rates are enhanced significantly for some decays involving $f_{2}^{\prime}$ meson, even with a small mixing angle.

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arXiv2012

Revisiting the B {\to} π ρ, π ω Decays in the Perturbative QCD Approach Beyond the Leading Order

We calculate the branching ratios and CP asymmetries of the $B \to πρ$, $πω$ decays in the perturbative QCD factorization approach up to the next-to-leading-order contributions. We find that the next-to-leading-order contributions can interfere with the leading-order part constructively or destructively for different decay modes. Our numerical results have a much better agreement with current available data than previous leading-order calculations, e.g., the next-to-leading-order corrections enhance the $B^0\rightarrow π^0ρ^0$ branching ratios by a factor 2.5, which is helpful to narrow the gaps between theoretic predictions and experimental data. We also update the direct CP-violation parameters, the mixing-induced CP-violation parameters of these modes, which show a better agreement with experimental data than many of the other approaches.

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arXiv2010

$B$-to-Glueball form factor and Glueball production in $B$ decays

We investigate transition form factors of $B$ meson decays into a scalar glueball in the light-cone formalism. Compared with form factors of $B$ to ordinary scalar mesons, the $B$-to-glueball form factors have the same power in the expansion of $1/m_B$. Taking into account the leading twist light-cone distribution amplitude, we find that they are numerically smaller than those form factors of $B$ to ordinary scalar mesons. Semileptonic $B\to Gl\barν$, $B\to Gl^+l^-$ and $B_s\to Gl^+l^-$ decays are subsequently investigated. We also analyze the production rates of scalar mesons in semileptonic $B$ decays in the presence of mixing between scalar $\bar qq$ and glueball states. The glueball production in $B_c$ meson decays is also investigated and the LHCb experiment may discover this channel. The sizable branching fraction in $B_c\to (π^+π^-)l^-\barν$, $B_c\to (K^+K^-)l^-\barν$ or $B_c\to (π^+π^-π^+π^-)l^-\barν$ could be a clear signal for a scalar glueball state.

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arXiv2010

Study light scalar meson property from heavy meson decays

In the SU(3) symmetry limit, the ratio $R\equiv\frac{{\cal B}(D^+\to f_0l^+ν)+ {\cal B}(D^+\to σl^+ν)}{{\cal B}(D^+\to a_0^0l^+ν)}$ is equal to 1 if the scalar mesons are $\bar qq$ states, while it is 3 if these mesons are tentraquark states. This ratio provides a model-independent way to distinguish the descriptions for light scalar mesons . It also applies to the $B^-\to Sl^-\barν$ and $\bar B^0\to J/ψ(η_c) S$ decays. The SU(3) symmetry breaking effect is found to be under control, which will not spoil our method. The branching fractions of the $D^+\to S l^+ν$, $B^-\to S l^-\barν$ and $\bar B^0\to J/ψ(η_c) S$ decays roughly have the order $10^{-4}$, $10^{-5}$ and $10^{-6}$, respectively. The B factory experiments and ongoing BEPC-II experiments are able to measure these channels and accordingly to provide the detailed information of the scalar meson inner structure.

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arXiv2009

The pure annihilation type B_c to M_2 M_3 decays in the perturbative QCD approach

In the standard model the two-body charmless hadronic $B_c$ meson decays can occur via annihilation diagrams only. In this work, we studied the $B_c \to PP, PV/VP,VV$ decays by employing the perturbative QCD (pQCD) factorization approach. From our calculations, we find that (a) the pQCD predictions for the branching ratios of the considered $B_c$ decays are in the range of $10^{-6}$ to $10^{-8}$; (b) for $B_c \to PV/VP, VV$ decays, the branching ratios of $ΔS= 0$ decays are much larger than those of $ΔS =1$ ones because the different Cabibbo-Kobayashi-Maskawa(CKM) factors are involved; (c) analogous to $B \to K η^{(\prime)}$ decays, we find $Br(B_c \to K^+ η^\prime) \sim 10 \times Br(B_c \to K^+ η)$, which can be understood by the destructive and constructive interference between the $η_q$ and $η_s$ contribution to the $B_c \to K^+ η$ and $B_c \to K^+ η^\prime$ decay; (d) the longitudinal polarization fractions of $B_c \to VV$ decays are in the range of $86%-95%$ and play the dominant role; and (e) there is no CP-violating asymmetries for the considered $B_c$ decays because only one type tree operators involved.

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