arXiv subjects

Cai-Dian Lu

Publications and source records attributed to Cai-Dian Lu.

At least 55 records · Page 3Linked to original sources

arXiv2009

The CKM suppressed $B(B_s) \to \bar D_{(s)}P,\bar D_{(s)}V,\bar D_{(s)}^P, \bar D_{(s)}^V$ decays in perturbative QCD approach

Although the two-body charmed decays $B_{(s)} \to \bar D_{(s)}^{(*)}P$ and $\bar D_{(s)}^{(*)}V$, where $P$($V$) denotes a light pseudoscalar(vector) meson, are CKM suppressed comparing with the $B_{(s)} \to D_{(s)}^{(*)}P$ and $ D_{(s)}^{(*)}V$ decays, they are important in the CKM angle $γ=ϕ_3$ extraction method. We investigated these decays in the perturbative QCD approach to the leading order of $m_D/m_B$ and $Λ_{\rm{QCD}}/m_D$ expansion. We find that the nonfactorizable emission diagrams and the annihilation diagrams are not negligible in many of these channels. The numerical results show that most channels have branching ratios with an order of $10^{-6}$ or $10^{-7}$. The ratio needed for the CKM angle $γ$ extraction is estimated as $r = \frac{|A(B^- \to \bar{D}^0 K^-)|}{|A(B^- \to D^0 K^-)|} = 0.092_{-0.003-0.003}^{+0.012+0.003},$ which is too small for the experiments. Some of the $ B_{(s)}\to \bar D_{(s)}^*V$ decays have a very large transversely polarized contribution that can reach 80%.

hep-ph↗

arXiv2009

The Clean Way to Identify a Scalar Glueball

The existence of a glueball has been a tough work for many years study. Utilizing the well developed QCD theory for $B$ meson decays, we propose a new way to identify whether a scalar glueball existed or not. In the presence of mixing between glueballs and ordinary scalar mesons, we explore the possibility to extract the mixing parameters from semileptonic B decays and nonleptonic B decays. We also point out a clean way to identify a glueball through $B_c$ decays.

hep-ph↗

arXiv2009

Anatomy of the pQCD Approach to the Baryonic Decays $Λ_b \to pπ, p K$

We calculate the CP-averaged branching ratios and CP-violating asymmetries for the two-body charmless hadronic decays $Λ_b \to p π, pK$ in the perturbative QCD (pQCD) approach to lowest order in $α_s$. The baryon distribution amplitudes involved in the factorization formulae are considered to the leading twist accuracy and the distribution amplitudes of the proton are expanded to the next-to-leading conformal spin (i.e., "P" -waves), the moments of which are determined from QCD sum rules. Our work shows that the contributions from the factorizable diagrams in $Λ_b \to p π, pK$ decays are much smaller compared to the non-factorizable diagrams in the conventional pQCD approach. We argue that this reflects the estimates of the $Λ_b \to p$ transition form factors in the $k_T$ factorization approach, which are found typically an order of magnitude smaller than those estimated in the light-cone sum rules and in the non-relativistic quark model. As an alternative, we adopt a hybrid pQCD approach, in which we compute the factorizable contributions with the $Λ_b \to p$ form factors taken from the light cone QCD sum rules. The non-factorizable diagrams are evaluated utilizing the conventional pQCD formalism which is free from the endpoint singularities. The predictions worked out here are confronted with the recently available data from the CDF collaboration on the branching ratios and the direct CP asymmetries for the decays $ Λ_b \to p π$, and $Λ_b \to p K$. The asymmetry parameter $α$ relevant for the anisotropic angular distribution of the emitted proton in the polarized $Λ_b$ baryon decays is also calculated for the two decay modes.

hep-ph↗

arXiv2009

$Λ_b \to p, Λ$ transition form factors from QCD light-cone sum rules

Light-cone sum rules for the $Λ_b \to p, Λ$ transition form factors are derived from the correlation functions expanded by the twist of the distribution amplitudes of $Λ_b$ baryon. In terms of the $Λ_b$ three-quark distribution amplitudes models constrained by the QCD theory, we calculate the form factors at small momentum transfers and compare the results with that estimated in the conventional light-cone sum rules (LCSR) and perturbative QCD approaches. Our results indicate that the two different version of sum rules can lead to the consistent numbers of form factors responsible for $Λ_b \to p$ transition. The $Λ_b \to Λ$ transition form factors from LCSR with the asymptotic $Λ$ baryon distribution amplitudes are found to be almost one order larger than that obtained in the $Λ_b$-baryon LCSR, implying that the pre-asymptotic corrections to the baryonic distribution amplitudes are of great importance. Moreover, SU(3) symmetry breaking effect between the form factors $f_1^{Λ_b \to p}$ and $f_1^{Λ_b \to Λ}$ are computed as $28^{+14}_{-8} %$ in the framework of $Λ_b$-baryon LCSR.

hep-ph↗

arXiv2009

Exclusive $B_s$ decays to the charmed mesons $D_s^+(1968,2317)$ in the standard model

The transition form factors of $\bar B_s^0\to D_{s}^+(2317)$ and $\bar B_s^0\to D_s^+(1968)$ at large recoil region are investigated in the light cone sum rules approach, where the heavy quark effective theory is adopted to describe the form factors at small recoil region. With the form factors obtained, we carry out a detailed analysis on both the semileptonic decays $\bar B_s^0\to D_s^+(1968,2317) l \barν_l$ and nonleptonic decays $B_s \to D_s^+(1968,2317) M$ with $M$ being a light meson or a charmed meson under the factorization approach. Our results show that the branching fraction of $\bar B_s^0\to D_s^+(2317) μ\barν_μ$ is around $2.3 \times 10^{-3}$, which should be detectable with ease at the Tevatron and LHC. It is also found that the branching fractions of $\bar B_s^0\to D_s^+(1968) l \barν_l$ are almost one order larger than those of the corresponding $B_s^0\to D_s^+(2317) l \barν_l$ decays. The consistency of predictions for $B_s \to D_s^+(1968,2317) L$ ($L$ denotes a light meson) in the factorization assumption and $k_T$ factorization also supports the success of color transparency mechanism in the color allowed decay modes. Most two-charmed meson decays of $B_s$ meson possess quite large branching ratios that are accessible in the experiments. These channels are of great importance to explore the hadronic structure of charmed mesons as well as the nonperturbative dynamics of QCD.

hep-ph↗

arXiv2009

$B \to K^{\ast}_0(1430) l^{+} l^{-}$ decays in supersymmetric theories

The weak decays of $B \to K^{\ast}_0(1430) l^{+} l^{-}$ ($l=μ, τ$) are investigated in Minimal Supersymmetric Standard Model (MSSM) and also in Supersymmetric (SUSY) SO(10) Grand Unified Models. Neutral Higgs bosons are the point of main focus in MSSM because they make quite a large contribution in exclusive $B \to X_{s} l^{+} l^{-}$ decays at large $\tanβ$ regions of parameter space of SUSY models, as part of SUSY contributions is proportional to $\tan^{3}β$. The analysis of decay rate, forward-backward asymmetries and lepton polarization asymmetries in $B \to K^{\ast}_0(1430) l^{+} l^{-}$ show that the values of these physical observables are greatly modified by the effects of neutral Higgs bosons. In SUSY SO(10) GUT model, the new physics contribution comes from the operators which are induced by the neutral Higgs boson penguins and also from the operators with chirality opposite to that of the corresponding Standard Model (SM) operators. SUSY SO(10) effects show up only in the decay $B \to K^{\ast}_0 μ^{+} μ^{-}$ where the transverse lepton polarization asymmetries deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries, the longitudinal and normal lepton polarization asymmetries are very mild. The transverse lepton polarization asymmetry is almost zero in SM and in MSSM model, whereas it can reach to -0.3 in SUSY SO(10) GUT model which could be seen at the future colliders; hence this asymmetry observable can be used to discriminate between different SUSY models.

hep-ph↗

arXiv2009

Revisiting B->phi pi Decays in the Standard Model

In the standard model (SM), we re-investigate the rare decay $B\to ϕπ$, which has been viewed as an ideal probe to detect the new physics signals beyond the SM. Contributions in the naive factorization method, the radiative corrections, the long-distance contributions, and the contributions due to the $ω$-$ϕ$ mixing are taken into account. We find that the tiny branching ratio in the naive factorization can be dramatically enhanced by the radiative corrections and the $ω$-$ϕ$ mixing effect, while the long-distance contributions are negligibly small. Assuming the Cabibbo-Kobayashi-Maskawa angle $γ=(58.6\pm 10)^\circ$ and the mixing angle $θ= -(3.0\pm 1.0)^\circ$, we obtain the branching ratios of $B\to ϕπ$ as $ {\rm Br}(B^\pm\to ϕπ^\pm)= (3.2 ^{+0.8-1.2}_{-0.7+1.8}) \times 10^{-8}$ and $ {\rm Br}(B^0 \to ϕπ^0) = (6.8 ^{+0.3-0.7}_{-0.3+1.0}) \times 10^{-9}$. If the future experiment reports a branching ratio of order $10^{-7}$ for $B^-\to ϕπ^-$ decay, it may not be a clear signal for any new physics scenario. In order to discriminate the large new physics contributions and those due to the $ω$-$ϕ$ mixing, we propose to measure the ratio of branching fractions of the charged and neutral B decay channel. We also study the direct CP asymmetries of these two channels, and the results are about $(-8.0^{+0.9+1.5}_{-1.0-0.1})%$ and $(-6.3^{-0.5+2.5}_{+0.7-2.5})%$ for $B^\pm\to ϕπ^\pm$ and $B^0 \to ϕπ^0$, respectively.

hep-ph↗

arXiv2008

FCNC-induced semileptonic decays of $J/ψ$ in the Standard Model

In this work, we calculate the form factors for $J/ψ\to \bar{D}^{(*)0}$ induced by the flavor changing neutral currents (FCNC) in terms of the QCD sum rules. Making use of these form factors, we further calculate the branching fractions of semileptonic decays $J/ψ\to \bar{D}^{(*)0} l ^+ l^-$ ($l=e, μ$). In particular, we formulate the matrix element $ $ with $T_{μν}$ being a tensor current, which was not fully discussed in previous literature. Our analysis indicates that if only the standard model (SM) applies, the production of single charmed mesons at the present electron-positron colliders is too small to be observed even the resonance effects are included, therefore if an anomalous production rates are observed, it would be a hint of new physics beyond SM. Even though the predicted branching ratios are beyond the reach of present facilities which can be seen from a rough order estimate, the more accurate formulation of the three point correlation function derived in this work has theoretical significance and the technique can also be applied to other places. In analog to some complicated theoretical derivations which do not have immediate phenomenological application yet, if the future experiments can provide sufficient luminosity and accuracy, the results would be helpful.

hep-ph↗

arXiv2008

Rare decays of $Λ_b \to Λγ$ and $Λ_b \to Λl^{+} l^{-}$ in universal extra dimension model

The exclusive weak decay of $Λ_b \to Λγ$ and $Λ_b \to Λl^{+} l^{-}$ are investigated in the Applequist-Cheng-Dobrescu model, which is an extension of the standard model in presence of universal extra dimensions. Employing the transition form factors obtained in the light-cone sum rues, we analyze how the invariant mass distribution, forward-backward asymmetry and polarization asymmetry of $Λ$ baryon of these decay modes can be used to constrain the only one additional free parameter with respect to the standard model, namely, the radius $R$ of the extra dimension. Our results indicate that the Kaluza-Klein modes can lead to approximately 25% suppression of the branching ratio of $Λ_b \to Λγ$, however, their contributions can bring about 10% enhancement to the decay rate of $Λ_b \to Λl^{+} l^{-}$. It is shown that the zero-position of forward-backward asymmetry of $Λ_b \to Λμ^{+} μ^{-}$ is sensitive to the compactification parameter $R$ in this scenario, while the measurement of polarizations of $Λ$ baryon in the $Λ_b$ decays is not suitable to provide some valuable information for the universal extra dimension model.

hep-ph↗

arXiv2008

B \to 0^{+}(1^{+}) + missing energy in Unparticle Physics

We examine the effects of an unparticle $\mathcal{U}$ as a possible source of missing energy in the p-wave decays of $B$ meson. The dependence of the differential branching ratio on the $K_{0}^{\ast}(K_{1}) -$% meson's energy is discussed in the presence of scalar and vector unparticle operators and significant deviation from the standard model value is found after addition of these operators. Finally, we have shown the dependence of branching ratio for the above said decays on the parameters of the unparticle stuff like the effective couplings, cutoff scale $Λ_{% \mathcal{U}}$ and the scale dimensions $d_{\mathcal{U}}$.

hep-ph↗

arXiv2008

Charmless Two-body $B(B_s)\to VP$ decays In Soft-Collinear-Effective-Theory

We provide the analysis of charmless two-body $B\to VP$ decays under the framework of the soft-collinear-effective-theory (SCET), where $V(P)$ denotes a light vector (pseudoscalar) meson. Besides the leading power contributions, some power corrections (chiraly enhanced penguins) are also taken into account. Using the current available $B\to PP$ and $B\to VP$ experimental data on branching fractions and CP asymmetry variables, we find two kinds of solutions in $χ^2$ fit for the 16 non-perturbative inputs which are essential in the 87 $B\to PP$ and $B\to VP$ decay channels. Chiraly enhanced penguins can change several charming penguins sizably, since they share the same topology. However, most of the other non-perturbative inputs and predictions on branching ratios and CP asymmetries are not changed too much. With the two sets of inputs, we predict the branching fractions and CP asymmetries of other modes especially $B_s\to VP$ decays. The agreements and differences with results in QCD factorization and perturbative QCD approach are analyzed. We also study the time-dependent CP asymmetries in channels with CP eigenstates in the final states and some other channels such as $\bar B^0/B^0\toπ^\pmρ^\mp$ and $\bar B_s^0/B_s^0\to K^\pm K^{*\mp}$. In the perturbative QCD approach, the $(S-P)(S+P)$ penguins in annihilation diagrams play an important role. Although they have the same topology with charming penguins in SCET, there are many differences between the two objects in weak phases, magnitudes, strong phases and factorization properties.

hep-ph↗

arXiv2008

Exclusive semileptonic decays of $Λ_b \to Λl^{+} l^{-}$ in supersymmetric theories

The weak decays of $Λ_b \to Λl^{+} l^{-}$ ($l=e, μ$) are investigated in Minimal Supersymmetric Standard Model (MSSM) and also in Supersymmetric (SUSY) SO(10) Grand Unified Models. In MSSM the special attention is paid to the Neutral Higgs Bosons (NHBs) as they make quite a large contribution in exclusive $B \to X_{s} l^{+} l^{-}$ decays at large $\tanβ$ regions of parameter space of SUSY models, since part of SUSY contributions is proportional to $\tan^{3}β$. The analysis of decay rate, forward-backward asymmetries, lepton polarization asymmetries and the polarization asymmetries of $Λ$ baryon in $Λ_b \to Λl^{+} l^{-}$ show that the values of these physical observables are greatly modified by the effects of NHBs. In SUSY SO(10) GUT model, the new physics contribution comes from the operators which are induced by the NHBs penguins and also from the operators having chirality opposite to that of the corresponding SM operators. SUSY SO(10) effects show up only in the decay $Λ_b \to Λ+τ^{+} τ^{-}$ where the longitudinal and transverse lepton polarization asymmetries are deviate significantly from the SM value while the effects in the decay rate, forward-backward asymmetries and polarization asymmetries of final state $Λ$ baryon are very mild. The transverse lepton polarization asymmetry in $Λ_b \to Λ+τ^{+} τ^{-}$ is almost zero in SM and in MSSM model. However, it can reach to -0.1 in SUSY SO(10) GUT model and could be seen at the future colliders; hence this asymmetry observable will provide us useful information to probe new physics and discriminate between different models.

hep-ph↗

arXiv2008

Charmless hadronic $B$ and $B_s$ decays in perturbative QCD approach

We review the perturbative QCD approach study of hadronic B decays. Utilizing the constrained parameters in these well measured decay channels, we study most of the possible charmless $B_s \to PP$, $PV$ and $VV$ decay channels in the perturbative QCD approach. In addition to the branching ratios and CP asymmetries, we also give predictions to the polarization fractions of the vector meson final states. The size of SU(3) breaking effect is also discussed. These predictions can be tested by the future LHCb experiment.

hep-ph↗

arXiv2008

Charmless Two-body $B(B_s)\to PP,VP$ decays In Soft-Collinear-Effective-Theory

We analyze the charmless two-body $B\to VP$ decays in the soft-collinear-effective-theory (SCET), where $V(P)$ denotes a light vector (pseudoscalar) meson. Using the current experimental data, we find two solutions in $χ^2$ fit for the 16 non-perturbative inputs responsible for the 87 $B\to PP$ and $B\to VP$ decay channels in SU(3) symmetry. Chirally enhanced penguins can only change several charming penguins sizably, since they share the same topology. The (S-P)(S+P) annihilation penguins in the perturbative QCD approach have the same topology with charming penguins in SCET, which play an important role in direct CP asymmetries.

hep-ph↗

arXiv2008

Rare Decays of Λ_b->Λ+ γand Λ_b ->Λ+ l^{+} l^{-} in the Light-cone Sum Rules

Within the Standard Model, we investigate the weak decays of $Λ_b \to Λ+ γ$ and $Λ_b \to Λ+ l^{+} l^{-}$ with the light-cone sum rules approach. The higher twist distribution amplitudes of $Λ$ baryon to the leading conformal spin are included in the sum rules for transition form factors. Our results indicate that the higher twist distribution amplitudes almost have no influences on the transition form factors retaining the heavy quark spin symmetry, while such corrections can result in significant impacts on the form factors breaking the heavy quark spin symmetry. Two phenomenological models (COZ and FZOZ) for the wave function of $Λ$ baryon are also employed in the sum rules for a comparison, which can give rise to the form factors approximately 5 times larger than that in terms of conformal expansion. Utilizing the form factors calculated in LCSR, we then perform a careful study on the decay rate, polarization asymmetry and forward-backward asymmetry, with respect to the decays of $Λ_b \to Λγ$, $Λl^{+}l^{-}$.

hep-ph↗

arXiv2008

Scalar mesons in weak semileptonic decays of $B_{(s)}$

The transition form factors of $B_{(s)} \to S$, with $S$ denoting a scalar meson, are investigated in the light-cone sum rules approach. The numerical values are approximately twice as large as that estimated in the light-front quark model and QCD sum rules approach. Using these form factors, we present the analysis of the decay rates for $B \to a_0(1450) l \barν_l $, $B \to K^{\ast}_0(1430) l \bar{l}$, $B_s \to K^{\ast}_0(1430) l \barν_l$ and $B_s \to f_0(1500) l \bar{l}$ with $l=e, μ, τ$. The results indicate that magnitudes of $BR(\bar{B}_0 \to a_0(1450) l \barν_l)$ and $BR(B_s \to K^{\ast}_0(1430) l \barν_l)$ can arrive at the order of $10^{-4}$, which can be measured in the future experiments to clarify the inner structure of scalar mesons. It is also observed that $BR(B \to K^{\ast}_0(1430) τ^+ τ^-)$ and $BR(B_s \to f_0(1500) τ^+ τ^-)$ are an order of magnitude smaller than the corresponding channels of $e^+ e^-$ and $μ^+ μ^-$ final states due to the heavily suppressed phase space . Moreover, the longitudinal lepton polarization asymmetry for $B \to K^{\ast}_0(1430) l \bar{l}$ and $B_s \to f_0(1500) l \bar{l}$ are also investigated, whose values are close to -1 for the $e^+ e^-$ and $μ^+ μ^-$ pair except the region close to the end points.

hep-ph↗

arXiv2008

Weak productions of new charmonium in semi-leptonic decays of B_c

We study the weak productions of novel heavy mesons, such as $η_c^{\prime}$, $h_c$, $h_c^{\prime}$, $χ_{c0}^{\prime}$, X(3940), Y(3940), X(3872), and Y(4260), in the semi-leptonic $B_c$ decays. Since there is still no definite answer for the components of X(3940), Y(3940), X(3872), Y(4260) so far, we will assign them as excited charmonium states with the possible quantum numbers constrained by the current experiments. As for the weak transition form factors, we calculate them in the framework of light-cone QCD sum rules approach, which is proved to be a powerful tool to deal with the non-perturbative hadronic matrix element. Our results indicate that different interpretations of X(3940) can result in remarkable discrepancy of the production rate in the $B_c$ decays, which would help to clarify the inner structure of the X(3940) with the forthcoming LHC-b experiments. Besides, the predicted large weak production rates of X(3872) and Y(3940) in $B_c$ decays and the small semi-leptonic decay rate for $B_c \to Y(4260)$ all depend on their quantum number $J^{PC}$ assignments. Moreover, the $S-D$ mixing of various vector charmonium states in the weak decay of $B_c$ is also discussed in this work. The future experimental measurements of these decays will test the inner structures of these particles, according to our predictions here.

hep-ph↗

arXiv2008

Lepton polarization asymmetry and forward backward asymmetry in exclusive B->K_1 tau^(+)tau^(-) decay in universal extra dimension scenario

Decay rate, forward-backward asymmetry and polarization asymmetries of final state leptons in B-> K_{1}tau ^{+}tau ^{-}, where K_{1} is the axial vector meson, are calculated in Standard Model and in the universal extra dimension (UED) model. The sensitivity of the observables on the compactification radius $R$, the only unknown paramter in UED model, is studied. Finally, the helicity fractions of the final state K_{1} are calculated and their dependence on the compactification radius is discussed. This analysis of helicity fraction is briefly extended to B->K^{*}l ^{+}l ^{-}(l =e,mu) and compared with the other approaches exist in the literature

hep-ph↗