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Cai-Dian Lü

Publications and source records attributed to Cai-Dian Lü.

At least 91 records · Page 5Linked to original sources
arXiv2007

Radiative charmless B_{(s)}\to V γand B_{(s)}\to A γdecays in pQCD approach

We study the radiative charmless $B_{(s)}\to V(A)γ$ decays in perturbative QCD (pQCD) approach to the leading order in $α_s$ (here $V$ and $A$ denotes vector mesons and two kinds of axial-vector mesons: $^3P_1$ and $^1P_1$ states, respectively.). Our predictions of branching ratios are consistent with the current available experimental data. We update all $B_{(s)}\to V$ form factors and give the predictions for $B\to A$ form factors using the recent hadronic inputs. In addition to the dominant factorizable spectator diagrams, which is form factor like, we also calculate the so-called ``power suppressed'' annihilation type diagrams, the gluonic penguin, charming penguin, and two photon diagrams. These diagrams give the main contributions to direct CP asymmetries, mixing-induced CP asymmetry variables, the isospin asymmetry and U-spin asymmetry variables. Unlike the branching ratios, these ratios or observables possess higher theoretical precision in our pQCD calculation, since they do not depend on the input hadronic parameters too much. Most of the results still need experimental tests in the on-going and forthcoming experiments.

hep-ph↗
arXiv2007

Study of $K^*_0(1430)$ and $a_0(980)$ from $B\to K^*_0(1430)π$ and $B\to a_0(980)K$ Decays

We use the decay modes $B \to K^*_0(1430) π$ and $B \to a_0(980) K$ to study the scalar mesons $K^*_0(1430)$ and $a_0(980)$ within perturbative QCD framework. For $B \to K^*_0(1430) π$, we perform our calculation in two scenarios of the scalar meson spectrum. The results indicate that scenario II is more favored by experimental data than scenario I. The important contribution from annihilation diagrams can enhance the branching ratios about 50% in scenario I, and about 30% in scenario II. The predicted branching ratio of $B \to a_0(980) K$ in scenario I is also less favored by the experiments. The direct CP asymmetries in $B \to K^*_0(1430) π$ are small, which are consistent with the present experiments.

hep-ph↗
arXiv2007

Twist-3 distribution amplitudes of scalar mesons from QCD sum rules

We study the twist-3 distribution amplitudes for scalar mesons made up of two valence quarks based on QCD sum rules. By choosing the proper correlation functions, we derive the moments of the scalar mesons up to the first two order. Making use of these moments, we then calculate the first two Gegenbauer coefficients for twist-3 distribution amplitudes of scalar mesons. It is found that the second Gegenbauer coefficients of scalar density twist-3 distribution amplitudes for $K^{*}_0$ and $f_0$ mesons are quite close to that for $a_0$, which indicates that the SU(3) symmetry breaking effect is tiny here. However, this effect could not be neglected for the forth Gegenbauer coefficients of scalar twist-3 distribution amplitudes between $a_0$ and $f_0$. Besides, we also observe that the first two Gegenbauer coefficients corresponding to the tensor current twist-3 distribution amplitudes for all the $a_0$, $K^{*}_0$ and $f_0$ are very small. The renormalization group evolution of condensates, quark masses, decay constants and moments are considered in our calculations. As a byproduct, it is found that the masses for isospin I=1, ${1 \over 2}$ scalar mesons are around $1.27 \sim 1.41$ GeV and $1.44 \sim 1.56$ GeV respectively, while the mass for isospin state composed of $\bar{s} s$ is $1.62 \sim 1.73$ GeV.

hep-ph↗
arXiv2006

Role of electromagnetic dipole operator in the electroweak penguin dominated vector meson decays of $B$ meson

The pure annihilation type decays $B^0_d\toϕγ$ and $B_s\toργ$ receive only color suppressed penguin contributions with a very small branching ratio in the standard model. When we include the previously neglected electromagnetic dipole operator, the branching ratios can be enhanced one order magnitude larger than previous study using QCD factorization approach. That is ${\cal BR}(\bar B^0_d\toϕγ)\simeq 1 \times 10^{-11}$ and ${\cal BR}(B_s\toργ) \sim (6-16)\times 10^{-10}$. The new effect can also give a large contribution, of order $10^{-9}$, to transverse polarization of $B\toϕρ$ and $B\to ωϕ$ which is comparable to the longitudinal part. These effects can be detected in the LHCb experiment and the Super-B factories.

hep-ph↗
arXiv2006

Study of W-exchange Mode $D^0 \to ϕ\bar K^0$

We calculate the branching ratio of $D^0 \to ϕ\bar K^0$ decay using the so-called perturbation QCD approach based on $k_T$ factorization. Our result shows this branching ratio is $(8.7 \pm1.4)\times 10^{-3}$, which is consistent with experimental data. We hope the CLEO-C and BES-III can measure it more accurately, which will help us to understand QCD dynamics and $D$ meson weak decays.

hep-ph↗
arXiv2006

Final State Interaction In $B\to KK$ Decays

We study the final state interaction effects in $B\to KK$ decays. We find that the $t$ channel one-particle-exchange diagrams cannot enhance the branching ratios of $\bar{B^0}\to K^0\bar{K^0}$ and $B^-\to K^0K^-$ very sizably. For the pure annihilation process $\bar{B^0}\to K^+K^-$, the obtained branching ratio by final state interaction is at ${\cal{O}}(10^{-8})$.

hep-ph↗
arXiv2006

Study of $B_{s}\to πρ$ decays in the perturbative QCD approach

In this note, we calculate the branching ratio and CP asymmetry parameters of $B_s\toπρ$ in the framework of perturbative QCD approach based on $k_T$ factorization. This decay can occur only via annihilation diagrams in the Standard Model. We find that (a)the charge averaged $Br(B_s\toπ^{+}ρ^{-}+π^{-}ρ^{+})$ is about $(9-12)\times10^{-7}$; $Br(B_s\toπ^{0}ρ^{0}) \simeq 4\times10^{-7}$; and (b) there are sizable CP asymmetries in the processes, which can be tested in the near future Large Hadron Collider beauty experiments (LHC-b) at CERN or BTeV experiments at Fermilab.

hep-ph↗
arXiv2005

Branching ratio and CP violation of $B_{s}\to πK$ decays in the perturbative QCD approach

In the framework of perturbative QCD approach, we calculate the branching ratio and CP asymmetry for $B_{s}^0(\bar{B}_{s}) \to π^{\pm} K^\mp$ and $B_{s}(\bar{B}_{s})\to π^{0}\bar{K}^{0}(K^{0})$ decays. Besides the usual factorizable diagrams, both non-factorizable and annihilation type contributions are taken into account. We find that (a) the branching ratio of $B_{s}^0(\bar{B}_{s}) \to π^{\pm} K^\mp$ is about $(6-10) \times 10^{-6}$; $Br(B_{s}(\bar{B}_{s})\to π^{0}\bar{K}^{0}(K^{0}))$ about $ (1-3) \times 10^{-7}$; and (b) there are large CP asymmetries in the two processes, which can be tested in the near future LHC-b experiments at CERN and BTeV experiments at Fermilab.

hep-ph↗
arXiv2005

Branching Ratio and CP Asymmetry of $B \to πη^{(\prime)}$ Decays in the Perturbative QCD Approach

We calculate the branching ratios and CP-violating asymmetries for $B^0 \to π^0 η^{(\prime)}$ and $B^+\to π^+ η^{(\prime)}$ decays in the perturbative QCD (pQCD) factorization approach here. We not only calculate the usual factorizable contributions, but also evaluate the non-factorizable and annihilation type contributions. Besides the current-current operators, the contributions from the QCD and electroweak penguin operators are also taken into account. The pQCD results for the CP-averaged branching ratios are $Br(B^+ \to π^+ η) \approx 4.1 \times 10^{-6}$, $Br(B^+ \to π^+ η^\prime) \approx 2.4 \times 10^{-6}$, and $Br(B^0 \to π^0 η^{(\prime)}) \approx 0.2 \times 10^{-6}$, which agree very well with the measured values or currently available experimental upper limits. We also predict large CP-violating asymmetries in these decays: $A_{CP}^{dir}(π^\pm \etap)\sim A_{CP}^{dir}(π^0 \etap)\sim -0.35 $, and $A_{CP}^{mix}(π^0 \etap)\sim 0.67$, but with large errors. The pQCD prediction for $A_{CP}^{dir}(π^\pm η)$ ($A_{CP}^{dir}(π^\pm η^\prime))$ has the same (opposite) sign with the primary measured values. Further improvements in both theory and experiments are needed to clarify this discrepancy.

hep-ph↗
arXiv2005

$B^0 \to ϕϕ$ Decay in Perturbative QCD Approach

The rare decay $B^0 \to ϕϕ$ can occur only via penguin annihilation topology in the standard model. We calculate this channel in the perturbative QCD approach. The predicted branching ratio is very small at ($10^{-8}$). We also give the polarization fractions, which shows that the transverse polarization contribution is comparable to the longitudinal one, due to a big transverse contribution from factorizable diagrams. The small branching ratio in SM, makes it sensitive to any new physics contributions.

hep-ph↗
arXiv2003

Constraints on the CKM angle $α$ from the measured CP asymmetries and branching ratios of $B \to π^+ π^-, π^+ π^0$ and $K^0π^+$ decays

In this paper, we draw constraints on the Cabibbo-Kobayashi-Maskawa (CKM) angle $α$ and the strong phase $δ$ from the experimental measurements of $\ssb$, the CP-violating asymmetries and branching ratios of $B \to π^+ π^-, π^+ π^0$ and $K^0 π^+$ decays. In the SM, the measured $\ssb$ leads to an upper limit on $α$: $α\leq 180^\circ-β$. Taking the weighted-average of the newest BaBar and Belle measurements of $\spp$ and $\app$ in $B^0 \to π^+π^-$ decay as the experimental input, we find the allowed range of angle $α$, $76^\circ \leq α\leq 135^\circ$ for $r=|P/T| =0.3 \pm 0.1 $. From the measured CP-averaged branching ratios of $B \to π^+ π^-, π^+ π^0$ and $K^0 π^+$ decays, we found an inequality, $\cosα \cosδ \geq 0.45$. The region of $70^\circ \leq α\leq 110^\circ$ is thus excluded by applying this inequality. The combined constraints on $α$ and $δ$ are $117^\circ \leq α\leq 135^\circ$ and $-160^\circ \leq δ\leq -132^\circ$ if we take $\spp=0.49 \pm 0.27$ and $\app=0.51 \pm 0.19$ as the experimental input. The new lower limit on the angle $α$ is dominated by the measured branching ratios considered in this paper, and is much stronger than those obtained before.

hep-ph↗
arXiv2003

Technicolor corrections on $B_{s,d} \to γγ$ decays in QCD factorization

Within the framework of the Top-color-assisted Technicolor (TC2) model, we calculate the new physics contributions to the branching ratios $\calb(B_{s,d} \to γγ)$ and CP violating asymmetries $\rcpm(B_{s,d} \to γγ)$ in the QCD factorization based on the heavy-quark limit $m_b \gg Λ_{QCD}$. Using the considered parameter space, we find that (a) for both $B_s\to γγ$ and $B_d \to γγ$ decays, the new physics contribution can provide a factor of two to six enhancement to their branching ratios, (b) for the $B_s \to γγ$ decay, its direct CP violation is very small in both the SM and TC2 model, and (c) the CP violating asymmetry $\rcpm(B_d \to γγ)$ is around the ten percent level in both the SM and TC2 model, but the sign of CP asymmetry in the TC2 model is different from that in the SM.

hep-ph↗
arXiv2002

Constraint on the CKM angle alpha from the experimental measurements of CP violation in B_d^0 --> pi^+ pi^- decay

In this paper, we study and try to find the constraint on the CKM angle alpha from the experimental measurements of CP violation in B_d^0 --> pi^+ pi^- decay, as reported very recently by BaBar and Belle Collaborations. After considering uncertainties of the data and the ratio r of penguin over tree amplitude, we found that strong constraint on both the CKM angle alpha and the strong phase delta can be obtained from the measured CP asymmetries S_{pi pi} and A_{pi pi}: (a) the ranges of 87 degrees <= alpha <= 131 degrees and 36 degrees <= delta <= 144 degrees are allowed by 1 sigma of the averaged data for r = 0.31; (b) for Belle's result alone, the limits on alpha and delta are 104 degrees <= alpha <= 139 degrees and 42 degrees <= delta <= 138 degrees for 0.32 <= r <= 0.41; and (c) the angle alpha larger than 90 degrees is preferred.

hep-ph↗
arXiv2001

$B\to πρ$, $πω$ Decays in Perturbative QCD Approach

We calculate the branching ratios and CP asymmetries for $B^0 \to π^+ρ^-$, $B^0 \to ρ^+π^-$, $B^+ \to ρ^+π^0$, $B^+ \to π^+ρ^0$, $B^0 \to π^0ρ^0$, $B^+ \to π^+ω$ and $B^0 \to π^0ω$ decays, in a perturbative QCD approach. In this approach, we calculate non-factorizable and annihilation type contributions, in addition to the usual factorizable contributions. Our result is in agreement with the measured branching ratio of $B^0/\bar B^0 \to π^\pmρ^\mp$, $B^\pm \to π^\pmρ^0$, $π^\pm ω$ by CLEO and BABAR collaboration. We also predict large CP asymmetries in these decays. These channels are useful to determine the CKM angle $ϕ_2$.

hep-ph↗
arXiv1998

$b\to s s \bar d$ Decay in Two Higgs Doublet Models

In the Standard Model, the box-diagram mediated decay $b\to s s \bar d$ is predicted to occur with an extremely small branching ratio of below $10^{-11}$, thus providing a safe testing ground for exposing new physics. We study this process in several Two Higgs Doublet Models and explore their parameter space, indicating where this process becomes observable.

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