arXiv subjects

Cai-Dian Lu

Publications and source records attributed to Cai-Dian Lu.

At least 19 recordsLinked to original sources

arXiv2023

Analysis of three-body charmless $B$-meson decays under the factorization-assisted topological-amplitude approach

We analyze quasi-two-body charmless $B$ decays $B_{(s)} \to P_1 V \to P_1 P_2 P_3$ with $V$ representing a vector resonant, and $P_{1,2,3}$ as a light pseudo-scalar meson, pion, kaon or $η^{(\prime)}$. The intermediate processes $B_{(s)} \to P_1 V $ are calculated in the factorization-assisted topological-amplitude approach and the vector resonant effects are described by the Breit-Wigner propagator, which successively decay to $P_1 P_2$ via strong interaction. Taking into account of all vector resonances in ground state, $ρ, K^*, ω, ϕ$, we present the related branching fractions, and calculate the virtual effects for $B_{(s)} \to π, K (ρ,ω\to) KK$. We also predict direct $\it{CP}$ asymmetries of three body B decay modes with $ρ, K^*$ resonances as intermediate states. Our predicted branching fractions of decay modes dominated by the color-favored tree diagram or the color-favored penguin diagram are consistent with the perturbative QCD approach's predictions as well as QCD factorization approach. While for those nonperturbative contribution dominated decay modes, the branching ratios in this work are in better agreement with current experimental data than the PQCD predictions and the QCD factorization results due to their shortage of the nonperturbative contributions or $1/m_b$ power corrections. Many of the decays channels, especially for direct $\it{CP}$ asymmetries, are waiting for the future experiments.

hep-ph↗

arXiv2022

First Lattice QCD determination of semileptonic decays of charmed-strange baryons $Ξ_c$

While the standard model is the most successfully theory to describe all interactions and constituents in elementary particle physics, it has been constantly examined for over four decades. Weak decays of charm quarks can measure the coupling strength of quarks in different families and serve as an ideal probe for CP violation. As the lowest charm-strange baryons with three different flavors, $Ξ_c$ baryons (made of $csu$ or $csd$) have been extensively studied in experiments at the large hadron collider and in electron-positron collision. However the lack of reliable knowledge in theory becomes the unavoidable obstacle in the way. In this work, we use the state-of-the-art Lattice QCD techniques, and generate 2+1 clover fermion ensembles with two lattice spacings, $a=(0.108{\rm fm},0.080{\rm fm})$. We then present the first {\it ab-initio} lattice QCD determination of form factors governing $Ξ_{c}\to Ξ\ell^+ν_{\ell}$, analogous with the notable $β$-decay of nuclei. Our theoretical results for decay widths are consistent with and about two times more precise than the latest measurements by ALICE and Belle collaborations. Together with experimental measurements, we independently determine the quark-mixing matrix element $|V_{cs}|$, which is found in good agreement with other determinations.

hep-lat↗

arXiv2021

Global Analysis of hadronic two-body B decays in the perturbative QCD approach

Based on the flavor structure of four-quark effective operators, we develop an automatic computation program to calculate hadronic two-body $B$ meson decay amplitudes, and apply it to their global analysis in the perturbative QCD (PQCD) approach. Fitting the PQCD factorization formulas for $B\to PP,VP$ decays at leading order in the strong coupling $α_s$ to measured branching ratios and direct CP asymmetries, we determine the Gegenbauer moments in light meson light-cone distribution amplitudes (LCDAs). It is found that most of the fitted Gegenbauer moments of the twist-2 and twist-3 LCDAs for the pseudoscalar meson $P$ ($P=π$, $K$) and vector meson $V$ ($V=ρ$, $K^*$) agree with those derived in QCD sum rules. The shape parameter for the $B_s$ meson distribution amplitude and the weak phase $ϕ_3(γ)=(75.1\pm2.9)^\circ$ consistent with the value in Particle Data Group are also obtained. It is straightforward to extend our analysis to higher orders and higher powers in the PQCD approach, and to the global determination of LCDAs for other hadrons.

hep-ph↗

arXiv2019

Extraction of the CKM phase $γ$ from charmless two-body B meson decays

Utilizing all the experimental measured charmless $B \to PP$, $PV$ decay modes, where $P(V)$ denotes a light pseudoscalar (vector) meson, we extract the CKM angle $γ$ by global fit. All the unknown hadronic parameters are fitted with $γ$ together from experimental data, so as to make the approach least model dependent. The different contributions for various decay modes are classified by topological weak Feynman diagram amplitudes, which are to be determined by the global fit. To improve the precision of this approach, we consider flavor SU(3) breaking effects of topological diagram amplitudes among different decay modes by including the form factors and decay constants. The fitted result for CKM angle $γ$ is $(69.8 \pm 2.1 \pm 0.9) ^{\degree}$. It is consistent with the current world average with a better precision.

hep-ph↗

arXiv2019

Sensitivity study of anomalous HZZ couplings at future Higgs factory

We study the sensitivity of constraining the model independent Higgs-Z-Z coupling under effective theory up to dimension-6 operators at the future Higgs factory. Utilizing the current conceptual design parameters of the Circular Electron Positron Collider, we give the experimental limits for the model independent operators by the total Higgsstrahlung cross section and angular distribution of Z boson decay in the Higgs factory. Especially, we give very small sensitivity limit for the CP violation parameter $\tilde g$, which will be a clear window to test the Standard Model and look for New Physics signal.

hep-ex↗

arXiv2018

Footprints of New Physics in $b\to cτν$ Transitions

In this work, we perform a combined analysis of the $R(D)$, $R(D^*)$, and $R(J/ψ)$ anomalies in a model-independent manner based on the general framework of the four-fermion effective field theory, paying special attention to the use of the hadronic form factors. For the $B\to D(D^*)$ transition form factors, we use the HQET parametrization that includes the higher order corrections of $\mathcal{O}(α_s,Λ_{\mathrm{QCD}}/m_{b,c})$ and was determined recently from a fit to lattice QCD and light-cone sum rule results in complementary kinematical regions of the momentum transfer. For the $B_c\to J/ψ(η_c)$ transitions, we use the form factors calculated in the covariant light-front quark model, which are found to be well consistent with the preliminary lattice results. With this particular treatment of hadronic matrix elements, in our analysis the two classes of vector operators are shown to be the most favored single new physics (NP) operators by the current experimental constraints within $2σ$ and the LEP1 data on $Br(B_c\to τν)$ as well as the minimum $χ^2$ fit, while the tensor operator is also allowed but severely constrained, and the scalar ones are excluded. Using the favored ranges and fitted values of the Wilson coefficients of the single NP operators, we also give a prognosis for the physical observables such as the ratios of decay rates ($R(D(D^*)), R(J/ψ(η_c))$) and other polarized observables as well as the $q^2$ distributions.

hep-ph↗

arXiv2018

Recent Anomalies in B Physics

$B$ physics plays important roles in searching for the new physics (NP) beyond the standard model (SM). Recently, some deviations between experimental data and SM predictions were reported, namely $R(D^{(*)})$, $P_5^\prime$ and $R_{K^{(*)}}$ anomalies. If these anomalies were further confirmed in future, they would be unambiguous hints of NP. Theoretically, in order to explain these anomalies, a large number of models have been proposed, such as models including leptoquark or $Z^\prime$. However, these new particles have not been discovered directly in LHC. Moreover, the models should pass the examination of $B_s\to μ^+μ^-$ and $B_s^0-\bar B_s^0$ mixing. In future, the analysis of data taken during the ongoing Run 2 of the LHC and the forthcoming Belle-II will present new insight both into the observables of interest and into new strategies to control uncertainties. Theoretically, the existed models should be further tested; and more NP models are welcomed to explain these anomalies simultaneously without affecting other measurements consistent with SM.

hep-ph↗

arXiv2018

Search for doubly heavy baryon via weak decays

Using the factorization approach and taking into account the final state interaction, we calculate the two body non-leptonic decays of doubly heavy baryons. After comparing the semi-leptonic decays and all possible hadronic decay channels, we found some channels with large branching ratios. Taking the detection efficiency into consideration, we suggest $Ξ_{cc}^{++}$ as the first search goal and $Ξ_{cc}^{++}\to Λ_c^+K^-π^+π^+$ and $Ξ_{cc}^{++}\toΞ_{c}^{+}π^{+}$ as the golden discovery channels with $Λ_c^+$ reconstructed by $pK^-π^+$ and $Ξ_{c}^+ \to p K^- π^+$, respectively.

hep-ph↗

arXiv2018

Lepton Flavor Violating Decays of $B$ and $K$ Mesons in Models with Extended Gauge Group

Lepton Flavor Violating (LFV) decays are forbidden in the Standard Model (SM) and to explore them one has to go beyond it. The flavor changing neutral current induced Lepton Flavor Conserving and LFV decays of $K$ and $B$ mesons are discussed in the gauge group $G = SU(2)_L\times U(1)_{Y_1}\times SU(2)_X$. The lepto-quark $X^{\pm 2/3}_μ$ corresponding to gauge group $ SU(2)_X$ allows the quark-lepton transitions and hence giving a framework to construct the effective Lagrangian for the LFV decays. The mass of lepto-quark $m_{X}$ provides a scale at which the gauge group $G$ is broken to the SM gauge group. Using the most stringent experimental limit $\mathcal{B}(K^{0}_{L}\to μ^{\mp}e^{\pm}) < 1.7 \times 10^{-12}$, the upper bound on the effective coupling constant $(\frac{G_{X}}{G_F})^2 < 1.1 \times 10^{-10}$ is obtained for certain pairing of lepton and quark generations in the representation $(2, \bar{2})$ of the group $G$. Later, the effective Lagrangian for the LFV meson decays for the gauge group $G = \left[SU(2)_{L}\times SU(2)_{R}\times U(1)_{Y_1^{\prime}}\right]\times SU(2)_{X}$ is constructed. Using $\mathcal{B}(K^{-} \to π^{-}ν\barν) = (1.7 \pm 1.1)\times 10^{-10}$, the bound on the ratio of effective couplings is obtained to be $\left(\frac{G_{X}}{G_{F}}\right)^2 < 10^{-10}$. A number of decay modes are discussed which provide a promising area to test this model in the current and future particle physics experiments.

hep-ph↗

arXiv2017

Global Analysis of Charmless $B$ Decays into Two Vector Mesons in Soft-Collinear Effective Theory

Under the framework of soft-collinear effective theory, we analyze the charmless $B\to VV$ decays in a global way at leading power in $1/m_b$ and leading order in $α_s$ with $V$ denoting a light vector meson. In the flavor SU(3) symmetry, decay amplitudes for the 28 decay modes are expressed in terms of 8 nonperturbative parameters. With 35 experimental results, we fit these 8 nonperturbative parameters. Annihilation contributions are neglected due to power suppression in the $m_b\to \infty$ limit, so we include in the fit the nonperturbative charm penguins, which will play an important role in understanding the direct CP asymmetries. Charming penguins are also responsible for the large transverse polarizations of penguin-dominated and color-suppressed decays. With the best fitted parameters, we calculate all possible physical observables of 28 decay modes, including branching fractions, direct CP asymmetries, and the complete set of polarization observables. Most of our results are compatible with the present experimental data when available, while the others can be examined on the ongoing LHCb experiment and the forthcoming Belle-II experiment. Moreover, the agreements and differences with results in QCD factorization and perturbative QCD approach are also discussed. A few observables are suggested to discriminate these different approaches.

hep-ph↗

arXiv2017

Charmless Two-Body B Meson Decays In Factorization Assisted Topological Amplitude Approach

We analyze charmless two-body non-leptonic $B$ decays under the framework of factorization assisted topological amplitude approach. Unlike the conventional flavor diagram approach, we consider flavor $SU(3)$ breaking effect assisted by factorization hypothesis for topological diagram amplitudes of different decay modes, by factorizing out the corresponding decay constants and form factors. The non-perturbative parameters of topology diagram magnitudes $χ$ and strong phase $ϕ$ are universal that can be extracted by $χ^2$ fit from current abundant experimental data of charmless $B$ decays. The number of free parameters and the $χ^2$ per degree of freedom are both reduced comparing with previous analysis. With these best fitted parameters, we predict branching fractions and $CP$ asymmetry parameters of nearly 100 $B_{u,d}$ and $B_s$ decay modes. The long-standing $ππ$ and $πK$-$CP$ puzzles are solved simultaneously.

hep-ph↗

arXiv2017

Spectra of heavy-light mesons in a relativistic model

The spectra and wave functions of heavy-light mesons are calculated within a relativistic quark model, which is based on a heavy-quark expansion of the instantaneous Bethe-Salpeter equation by applying the Foldy-Wouthuysen transformation. The kernel we choose is the standard combination of linear scalar and Coulombic vector. The effective Hamiltonian for heavy-light quark-antiquark system is calculated up to order $1/m_Q^2$. Our results are in good agreement with available experimental data except for the anomalous $D_{s0}^*(2317)$ and $D_{s1}(2460)$ states. The newly observed heavy-light meson states can be accommodated successfully in the relativistic quark model with their assignments presented. The $D_{sJ}^*(2860)$ can be interpreted as the $|1^{3/2}D_1\rangle$ and $|1^{5/2}D_3\rangle$ states being members of the 1D family with $J^P=1^-$ and $3^-$.

hep-ph↗

arXiv2017

Charmless $B_{(s)}\to VV$ Decays in Factorization-Assisted Topological-Amplitude Approach

Within the factorization-assisted topological-amplitude approach, we studied the 33 charmless $B_{(s)} \to VV$ decays, where $V$ stands for a light vector meson. According to the flavor flows, the amplitude of each process can be decomposed into 8 different topologies. In contrast to the conventional flavor diagrammatic approach, we further factorize each topological amplitude into decay constant, form factors and unknown universal parameters. By $χ^2$ fitting 46 experimental observables, we extracted 10 theoretical parameters with $χ^2$ per degree of freedom around 2. Using the fitted parameters, we calculated the branching fractions, polarization fractions, CP asymmetries and relative phases between polarization amplitudes of each decay mode. The decay channels dominated by tree diagram have large branching fractions and large longitudinal polarization fraction. The branching fractions and longitudinal polarization fractions of color-suppressed decays become smaller. Current experimental data of large transverse polarization fractions in the penguin dominant decay channels can be explained by only one transverse amplitude of penguin annihilation diagram. Our predictions of those not yet measured channels can be tested in the ongoing LHCb experiment and the Belle-II experiment in future.

hep-ph↗

arXiv2016

Two-body Charmed $B$ Meson Decays In Factorization Assisted Topological Amplitude Approach

We analyze the two-body charmed $B$ meson decays $B_{u,d,s} \to D^{(*)}P(V)$ in the factorization assisted topological amplitude approach, where $P(V)$ denoting a light pseudoscalar (vector) meson. Different from the conventional topological diagram approach, flavor $SU(3)$ symmetry breaking effects are taken into account. Therefore only four universal nonperturbative parameters are introduced to describe the contribution from non-factorization diagrams for all the decay channels. The number of free parameters and the $χ^2$ per degree of freedom are both significantly reduced comparing with the conventional topological diagram approach. With the 4 fitted parameters, we predict the branching fractions of 120 decay modes induced by both $b\to c$ and $b\to u$ transitions, which are well consistent with the measured data or to be tested on the future experiments. We also investigated the relative size of different topological diagrams, isospin violation, flavor $SU(3)$ symmetry breaking effects, compared with previous approaches.

hep-ph↗

arXiv2015

Analysis of Two-body Charmed $B$ Meson Decays in Factorization-Assisted Topological-Amplitude Approach

Within the factorization-assisted topological-amplitude approach, we study the two-body charmed $B$ meson decays $B_{u,d,s} \to D^{(*)}M$, with $M$ denoting a light pseudoscalar (or vector) meson. The meson decay constants and transition form factors are factorized out from the hadronic matrix element of topological diagrams. Therefore the effect of SU(3) symmetry breaking is retained, which is different from the conventional topological diagram approach. The number of free nonperturbative parameters to be fitted from experimental data is also much less. Only four universal nonperturbative parameters $χ^C$, $ϕ^C$, $χ^E$ and $ϕ^E$ are introduced to describe the contribution of the color suppressed tree and $W$-exchanged diagrams for all the decay channels. With the fitted parameters from 31 decay modes induced by $b\to c$ transition, we then predict the branching fractions of 120 decay modes induced by both $b\to c$ and $b\to u$ transitions. Our results are well consistent with the measured data or to be tested in the LHCb and Belle-II experiments in the future. Besides, the SU(3) symmetry breaking, isospin violation and $CP$ asymmetry are also investigated.

hep-ph↗

arXiv2015

The $B_c\rightarrow ψ(2S)π$, $η_c(2S)π$ decays in the perturbative QCD approach

Nonleptonic two body $B_c$ decays including radially excited $ψ(2S)$ or $η_c(2S)$ mesons in the final state are studied using the perturbative QCD approach based on $k_T$ factorization. The charmonium distribution amplitudes are extracted from the $n = 2, l = 0$ Schr$\ddot{o}$dinger states for the harmonic oscillator potential. Utilizing these distribution amplitudes, we calculate the numerical results of the $B_c\rightarrow ψ(2S),η_c(2S)$ transition form factors and branching fractions of $B_c\rightarrow ψ(2S)π, η_c(2S)π$ decays. The ratio between two decay modes $B_c\rightarrow ψ(2S)π$ and $B_c\rightarrow J/ψπ$ is compatible with the experimental data within uncertainties, which indicate that the harmonic oscillator wave functions for $ψ(2S)$ and $η_c(2S)$ work well. It is found that the branching fraction of $B_c\rightarrow η_c(2S)π$, which is dominated by the twist-3 charmonium distribution amplitude, can reach the order of $10^{-3}$. We hope it can be measured soon in the LHCb experiment.

hep-ph↗

arXiv2015

Pure Annihilation Type $B \to K_0^{\pm}(1430)K^{()\mp}$ Decays in the Family Non-universal $Z^\prime$ Model

By assuming that the scalar meson $K_0^*(1430)$ belongs to the first excited states or the lowest lying ground states, we study the pure annihilation-type decays $B \to K_0^{*\pm}(1430)K^{(*)\mp}$ in the QCD factorization approach. Within the standard model, the branching fractions are at the order of $10^{-8}-10^{-7}$, which is possible to be measured in the ongoing LHCb experiment or forthcoming Belle-II experiment. We also study these decays in the family non-universal $Z^\prime$ model. The results show that if $m_{Z^\prime}\approx 600\mathrm{GeV}$ ($ζ=0.02$), both the branching fractions and $CP$ asymmetries of $\overline B^0\to K_0^{*+}(1430)K^-$ could be changed remarkably, which provides us a place for probing the effect of new physics. These results could be used to constrain the parameters of $Z^\prime$ model.

hep-ph↗

arXiv2015

Study of $B \to K_0^(1430)K^{()}$ decays in QCD Factorization Approach

Within the QCD factorization approach, we calculate the branching fractions and $CP$ asymmetry parameters of 12 $B \to K_0^*(1430)K^{(*)}$ decay modes under the assumption that the scalar meson $K_0^*(1430)$ is the first excited state or the lowest lying ground state in the quark model. We find that the decay modes with the scalar meson emitted, have large branching fractions due to the enhancement of large chiral factor $r_χ^{K_0^*}$. The branching fractions of decays with the vector meson emitted, become much smaller owing to the smaller factor $r_χ^{K^*}$. Moreover, the annihilation type diagram will induce large uncertainties because of the extra free parameter dealing with the endpoint singularity. For the pure annihilation type decays, our predictions are smaller than that from PQCD approach by 2-3 orders of magnitudes. These results will be tested by the ongoing LHCb experiment, forthcoming Belle-II experiment and the proposing circular electron-positron collider.

hep-ph↗