Searcharxiv⌕ Search

arXiv subjects

Cai-Dian Lu

Publications and source records attributed to Cai-Dian Lu.

At least 73 records · Page 4Linked to original sources
arXiv2008

Study Pure Annihilation Decays $B_s^0(\bar B_s^0)\to D^{\pm}π^{\mp}$ in PQCD Approach

The rare decays $B_s^0\to D^\pm π^\mp$ and $\bar B_s^0\to D^\mp π^\pm$ can occur only via annihilation type diagrams in the standard model. In this paper, we calculate branching ratios of these decays in perturbative QCD approach ignoring soft final state interaction. From our calculation, we find that their branching ratios are at $\mathcal{O}(10^{-6})$ with large CP asymmetry, which may be measured in LHC-b experiment in future.

hep-ph↗
arXiv2008

Weak decays of $J/ψ$: the non-leptonic case

In our previous study, we calculated the transition from factors of $J/ψ\to D^{(*)}_{(s)}$ using the QCD sum rules. Based on the factorization approximation, the obtained form factors can be applied to evaluate the weak non-leptonic decay rates of $J/ψ\to D^{(*)}_{(s)}+M$, where $M$ stands for a light pseudoscalar or vector meson. We predict that the branching ratio for inclusive non-leptonic two-body weak decays of $J/ψ$ which are realized via the spectator mechanism, can be as large as $1.3 \times 10^{-8}$, in particular, the branching ratio of $J/ψ\to D^{*\pm}_s+ρ^\mp$ can reach $5.3 \times 10^{-9}$. Such values will be marginally accessed by the ability of BESIII which will begin running very soon.

hep-ph↗
arXiv2008

Measuring $D^0-\bar D^0$ mixing in $D^0(\bar D^0)\to f_0(980) K^{*}$ and more

We investigate the $D^0-\bar D^0$ mixing through the doubly Cabibbo suppressed (DCS) channel $D^0\to f_0(980)K^{*0}$ and its charge conjugate channel, in which the $K^{*0}$ meson is reconstructed in both $K^+π^-$ and $K_Sπ^0$ final state. Although the decay $D^0\to f_0(980)K^{*}$ has a small branching ratio, the final state mesons are relatively easy to identify. The $f_0(980)$ meson can be replaced by $π^+π^-$ in which $π^+π^-$ form an $S$-wave state, or a longitudinally polarized vector meson $ρ^0,ω$. All mixing parameters, including the mass difference and decay width difference, can be extracted by studying the time-dependent decay width of these channels. We show that the method is valid in all regions for mixing parameters and it does not depend on the strong phase difference.

hep-ph↗
arXiv2007

Lepton flavor violating processes in unparticle physics

We study the virtual effects of unparticle physics in the lepton flavor violating processes $M^0\to l^+l'^-$ and $e^+e^-\to l^+l'^-$ scattering, where $M^0$ denotes the pseudoscalar mesons: $π^0,K_L, D_0,B_0,B_s^0$ and $l,l'$ denote two different lepton flavors. For the decay of $B^0\to l^+l'^-$, there is no constraint from the current experimental upper bounds on the vector unparticle coupling with leptons. The constraint on the coupling constant between scalar unparticle field and leptons is sensitive to the scaling dimension of the unparticle $d_{\cal U}$. For the scattering process $e^-e^+\to l^-l'^+$, there is only constraint from experiments on the vector unparticle couplings with leptons but no constraint on the scalar unparticle. We study the $\sqrt s$ dependence of the cross section $ \frac{1}σ \frac{dσ}{d\sqrt s}$ of $e^+e^-\to l^-l'^+$ with different values of $d_{\cal U}$. If $d_{\cal U}=1.5$, the cross section is independent on the center mass energy. For $d_{\cal U}>1.5$, the cross section increases with $\sqrt s$.

hep-ph↗
arXiv2007

Charmless non-leptonic B_s decays to PP, PV and VV final states in the pQCD approach

We calculate the CP-averaged branching ratios and CP-violating asymmetries of a number of two-body charmless hadronic decays $\bar{B_s^0} \to PP, PV, VV$ in the perturbative QCD (pQCD) approach to leading order in $α_s$ (here $P$ and $V$ denote light pseudoscalar and vector mesons, respectively). The mixing-induced CP violation parameters are also calculated for these decays. We also predict the polarization fractions of $B_s \to VV$ decays and find that the transverse polarizations are enhanced in some penguin dominated decays such as $\bar{B_s^0} \to K ^{*}\bar{K^{*}}$, $K ^{*}ρ$. Some of the predictions worked out here can already be confronted with the recently available data from the CDF collaboration on the branching ratios for the decays $ \bar{B_s^0} \to K^+π^-$, $ \bar{B_s^0} \to K^+K^-$ and the CP-asymmetry in the decay $ \bar{B_s^0} \to K^+π^-$, and are found to be in agreement within the current errors. A large number of predictions for the branching ratios, CP-asymmetries and vector-meson polarizations in $\bar{B_s^0}$ decays, presented in this paper and compared with the already existing results in other theoretical frameworks, will be put to stringent experimental tests in forthcoming experiments at Fermilab, LHC and Super B-factories.

hep-ph↗
arXiv2007

Heavy-to-light form factors on the light cone

The light cone method provides a convenient non-perturbative tool to study the heavy-to-light form factors. We construct a light cone quark model utilizing the soft collinear effective theory. In the leading order of effective theory, the ten $B$ to light physical form factors are reduced to three universal form factors which can be calculated as overlaps of hadron light front wave functions in the light cone quark model. The numerical results show that the leading contribution is close to the results from other approaches. The $q^2$ dependence of the heavy-to-light form factors are also presented.

hep-ph↗
arXiv2007

QCD in hadronic B decays

The perturbative QCD approach is based on $k_T$ factorization, including the Sudakov form factors so that to avoid the endpoint singularity. In this approach, we calculate the charmless B decays like $B\to ππ$ decays etc. to produce the right number of branching ratios and also CP asymmetry parameters. For final states with at least one charmed meson, like $B\to Dπ$ decays, our results also agree with the experiments.

hep-ph↗
arXiv2007

The study of $B_c^- \to X(3872)π^-(K^-)$ Decays in the Covariant Light-Front Approach

In the covariant light-front quark model, we calculate the form factors of $B_c^-\to J/ψ$ and $B_c^-\to X(3872)$. Since the factorization of the exclusive processes $B_c^- \to J/ψπ^-(K^-)$ and $B_c^- \to X(3872)π^-(K^-)$ can be proved in the soft-collinear effective theory, we can get the branching ratios for these decays easily from the form factors. Taking the uncertainties into account, our results for the branching ratio of $B_c^-\to J/ψπ^-(K^-)$ are consistent with the previous studies. By identifying X(3872) as a $1^{++}$ charmonium state, we obtain ${\cal BR}(B_c^-\to X(3872)π^-)=(1.7^{+0.7+0.1+0.4}_{-0.6-0.2-0.4}) \times 10^{-4}$ and ${\cal BR}(B_c^-\to X(3872)K^-)=(1.3^{+0.5+0.1+0.3}_{-0.5-0.2-0.3})\times 10^{-5}$. If assuming X(3872) as a $1^{--}$ state, the branching ratios will be one order magnitude larger than those of $1^{++}$ state. These results can be easily used to test the charmonium description for this mysterious meson X(3872) at LHCb experiment.

hep-ph↗
arXiv2007

Exclusive processes $e^+e^-\to VP$ in $k_T$ factorization

The exclusive processes $e^+e^-\to VP$, in the region of which the final state meson momentum is much larger than the hadronic scale $Λ_{QCD}$, are studied in the framework of PQCD approach based on the $k_T$ factorization. Including the transverse momentum distribution in the light cone wave functions, our results are consistent with the experimental measurements. According to our results, many processes have large enough cross sections to be detected at $\sqrt s=10.58$ GeV. The $s$ dependence of the cross section has been directly studied and our result indicates that the $1/s^3$ scaling is more favored than $1/s^4$. We also find that the gluonic contribution for the processes involving $η^{(')}$ is tiny.

hep-ph↗
arXiv2007

Diquarks and the Semi-Leptonic Decay of $Λ_{b}$ in the Hybrid Scheme

In this work we use the heavy-quark-light-diquark picture to study the semileptonic decay $Λ_b \to Λ_c+l+\barν_l$ in the so-called hybrid scheme. Namely, we apply the heavy quark effective theory (HQET) for larger $q^2$ (corresponding to small recoil), which is the invariant mass square of $l+\barν$, whereas the perturbative QCD approach for smaller $q^2$ to calculate the form factors. The turning point where we require the form factors derived in the two approaches to be connected, is chosen near $ρ_{cut}=1.1$. It is noted that the kinematic parameter $ρ$ which is usually adopted in the perturbative QCD approach, is in fact exactly the same as the recoil factor $ω=v\cdot v'$ used in HQET where $v$, $v'$ are the four velocities of $Λ_b$ and $Λ_c$ respectively. We find that the final result is not much sensitive to the choice, so that it is relatively reliable. Moreover, we apply a proper numerical program within a small range around $ρ_{cut}$ to make the connection sufficiently smooth and we parameterize the form factor by fitting the curve gained in the hybrid scheme. The expression and involved parameters can be compared with the ones gained by fitting the experimental data. In this scheme the end-point singularities do not appear at all. The calculated value is satisfactorily consistent with the data which is recently measured by the DELPHI collaboration within two standard deviations.

hep-ph↗
arXiv2006

A study on the radiative dileptonic decays $B^0(B_s)\toγ\ell^+\ell^-$

We study the rare radiative dileptonic decays $B^0(B_s)\to γ\ell^+\ell^-$ ($\ell=e,μ$) in the standard model. By using the $B$ meson wave function constrained by non-leptonic decays, the branching ratios turn out to be of the order of $10^{-9}$ for $B_s\toγμ^+μ^-$, $γe^+ e^-$ and $10^{-10}$ for $B^0\toγμ^+μ^-$, $γe^+ e^-$. Based on the study, these decays are accessible at the near future LHC-b experiment, which are useful to determine the $B(B_s)$ wave function.

hep-ph↗
arXiv2006

Study of scalar mesons f_0(980) and f_0(1500) from $B \to f_0(980) K$ and $B \to f_0(1500) K$ Decays

Within perturbative QCD approach based on $k_T$ factorization, we analyze the scalar mesons $f_0(980)$ and $f_0(1500)$ productions in B decays. By identifying $f_0(980)$ as the composition of $\bar ss$ and $\bar nn=(\bar uu+\bar dd)/\sqrt2$, we calculate the exclusive decays $B\to f_0(980) K$. We find that the non-factorization $f_0$-emission diagrams can give larger contribution to the branching ratio, than the previous PQCD calculation. Our new results can explain the current experimental data well. Under the assumption of quarkonium dominance, we study the branching ratio of decays $B\to f_0(1500) K$. The results show that in the two-quark picture of $f_0$ meson the contribution from $\bar s s$ component is at the similar size as that from the $\bar n n$ component. Comparing with the data, our results show the preference of $f_0(1500)$ as a member of the ground state of scalar $\bar qq$ nonet. Similar results can also apply to $f_0(1370)$ and $f_0(1710)$, if these mesons are dominated by the quarkonium content. With more experimental data in future, these studies will help us understand the intrinsic characters of these scalar mesons.

hep-ph↗
arXiv2006

Annihilation Type Radiative Decays of $B$ Meson in Perturbative QCD Approach

With the perturbative QCD approach based on $k_T$ factorization, we study the pure annihilation type radiative decays $B^0 \to ϕγ$ and $B^0\to J/ψγ$. We find that the branching ratio of $B^0 \to ϕγ$ is $(2.7^{+0.3+1.2}_{-0.6-0.6})\times10^{-11}$, which is too small to be measured in the current $B$ factories of BaBar and Belle. The branching ratio of $B^0\to J/ψγ$ is $({4.5^{+0.6+0.7}_{-0.5-0.6}})\times10^{-7}$, which is just at the corner of being observable in the $B$ factories. A larger branching ratio $BR(B_s^0 \to J/ψγ) \simeq 5 \times 10^{-6}$ is also predicted. These decay modes will help us testing the standard model and searching for new physics signals.

hep-ph↗
arXiv2006

Polarization Study in B Decays to Vector Final States

The small longitudinal polarization fractions (50%) of $B \to ϕK^*$ measured by B factories contradict with the naive theoretical counting rules. We review the current theoretical status of the $B\to VV$ decay studies and calculate many of them in the perturbative QCD factorization approach based on $k_T$ factorization. We find that the penguin annihilation and non-factorizable emission diagrams can enhance the transverse polarization fractions. The PQCD results agree with experiments for the measured $B\to ϕK^*$, $B\to ρK^*$ and $B\to ρρ$ channels, and we also predict new results (some different from other approaches) for those not yet measured channels.

hep-ph↗
arXiv2006

Study of $B\to K^* ρ, K^*ω$ Decays with Polarization in Perturbative QCD Approach

The $B \to K^{*}ρ$, $ K^{*}ω$ decays are useful to determine the CKM angle $ϕ_3=γ$. Their polarization fractions are also interesting since the polarization puzzle of the $B\to ϕK^*$ decay. We study these decays in the perturbative QCD approach based on $k_T$ factorization. After calculating of the non-factorizable and annihilation type contributions, in addition to the conventional factorizable contributions, we find that the contributions from the annihilation diagrams are crucial. They give dominant contribution to the strong phases and suppress the longitudinal polarizations. Our results agree with the current existing data. We also predict a sizable direct CP asymmetries in $B^+ \to K^{*+}ρ^0$, $B^0 \to K^{*+}ρ^-$, and $B^+ \to K^{*+}ω$ decays, which can be tested by the oncoming measurements in the B factory experiments.

hep-ph↗
arXiv2006

Branching Ratio and Polarization of $B\toρ(ω)ρ(ω)$ Decays in Perturbative QCD Approach

In this work, we calculated the branching ratios, polarization fractions and CP asymmetry of decay modes $B\toρ(ω)ρ(ω)$ in the Perturbative QCD approach, which is based on $\mathbf{k}_T$ factorization. After calculation, we find the the branching ratios of $B^0 \to ρ^+ ρ^-$, $B^+ \to ρ^+ ρ^0$ and $B^+ \to ρ^+ ω$ are at the order of $10^{-5}$, and their longitudinal polarization fractions are more than 90%. The above results agree with BarBar's measurements. We also predict the branching ratios and polarizations of $B^0 \to ρ^0 ρ^0$, $B^0 \to ρ^0 ω$ and $B^0 \to ωω$, which will be measured in future. We predicted the CP asymmetry of $B^0 \to ρ^+ ρ^-$ and $B^+ \to ρ^+ ρ^0$, which will play important role in determining angle $α$.

hep-ph↗
arXiv2005

Rare decays of B-> J/ψD^(*) and B->η_c D^(*)in pQCD Approach

Motivated by the recent measurement of the upper limit of ${B}^0 \to J/ψD$ branching ratio, which is important in accounting for the soft $J/ψ$ production in B decays, we investigate ${B}^0 \to J/ψD^{(\star)}$ and $η_c D^{(\star)}$ decays in perturbative QCD approach based on $k_T$ factorization. Being pure annihilation (W-exchange) decays, these branching ratios are estimated to be at the order of $10^{-5} \sim 10^{-7}$, which are just at the corner of being observable at the $B$ factories. The measurements of these decay channels may help us to understand the QCD dynamics in the corresponding energy scale, especially the reliability of pQCD approach to these processes.

hep-ph↗