arXiv subjects

Zhi-Tian Zou

Publications and source records attributed to Zhi-Tian Zou.

At least 55 records · Page 3Linked to original sources

arXiv2017

Study of $B_c \to DS$ Decays in PQCD Approach

Within the framework of perturbative QCD approach based on $k_T$ factorization, we studied 40 $B_c \to DS$ decay modes in the leading order and leading power, where "S" stands for the light scalar meson. Under two different scenarios (S1 and S2) for the description of scalar mesons, we explored the branching fractions and related CP asymmetries. As a heavy meson consisting of two heavy quarks with different flavor, the light-cone distribution amplitude of $B_c$ meson has not been well defined, so the $δ$-function is adopted. The contributions of emission diagrams are suppressed by the vector decay constants and CKM elements, the contributions of annihilation are dominant. After the calculation, we found some branching fractions are in the range of $[10^{-5}, 10^{-4}]$, which could be measured in the current LHCb experiment, and other decays with smaller branching fractions will be tested at the high-energy colliders in future. Furthermore, some decay modes have large CP asymmetries, but they are unmeasurable currently due to the small branching fractions.

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arXiv2017

Nonleptonic charmless decays of $B_c\to TP, TV$ in the perturbative QCD approach

Two-body charmless hadronic $B_c$ decays involving a light $1^3\!P_2$-tensor($T$) meson are investigated for the first time within the framework of perturbative QCD(pQCD) at leading order, in which the other meson is the lightest pseudoscalar($P$) or vector($V$) state. The concerned processes can only occur through the pure weak annihilation topology in the standard model. We predict the CP-averaged branching ratios and polarization fractions of those considered decays in Cabibbo-Kobayashi-Maskawa(CKM) favored and suppressed modes. Phenomenologically, several modes$-$such as the $B_c \to K_2^*(1430) K$ and the CKM-favored $B_c \to TV-$have large decay rates of $10^{-6}$, which are expected to be detected at Large Hadron Collider experiments in the near future. Moreover, all of the $B_c \to TV$ modes are governed by the longitudinal amplitudes in the pQCD calculations and the corresponding fractions vary around $78\%$-$98\%$. A confirmation of these results could prove the reliability of the pQCD approach used here and further shed some light on the annihilation decay mechanism.

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arXiv2017

Cabibbo-Kobayashi-Maskawa-favored $B$ decays to a scalar meson and a $D$ meson

Within the perturbative QCD approach, we investigated the Cabibbo-Kobayashi-Maskawa-favored $B \to \overline{D} S$ ("$S$" denoting the scalar meson) decays on the basis of the two-quark picture. Supposing the scalar mesons are the ground states or the first excited states, we calculated the the branching ratios of 72 decay modes. Most of the branching ratios are in the range $10^{-4}$ to $10^{-7}$, which can be tested in the ongoing LHCb experiment and the forthcoming Belle-II experiment. Some decays, such as $B^+ \to \overline{D}^{(*)0} a_0^+(980/1450)$ and $B^+ \to D^{(*)-} a_0^+(980/1450)$, could be used to probe the inner structure and the character of the scalar mesons, if the experiments are available. In addition, the ratios between the $Br(B^0\to \overline{D}^{(*)0}σ)$ and $Br(B^0\to \overline{D}^{(*)0}f_0(980))$ provide a potential way to determine the mixing angle between $σ$ and $f_0(980)$. Moreover, since in the standard model these decays occur only through tree operators and have no $CP$ asymmetries, any deviation will be signal of the new physics beyond the standard model.

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arXiv2017

Doubly-Heavy Baryon Weak Decays: $Ξ_{bc}^{0}\to pK^{-}$ and $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$

Doubly-heavy baryons, with two heavy and one light quarks, are expected to exist in QCD and their masses have been predicted in the quark model. However their existence is not well established so far in experiment. In this work, we explore the possibility of searching for $Ξ_{bc}$ and $Ξ_{cc}^{+}$ in the $W$-exchange processes, $Ξ_{bc}^{0}\to pK^{-}$ and $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$. On the basis of perturbative calculations, we estimate the branching ratio of the first decay as ${\cal BR}(Ξ_{bc}^0\to p^+ K^-)\approx3.21\times {\cal R}^2_f \times {\cal R}_τ\times 10^{-7}$, where ${\cal R}_f$ (${\cal R}_τ$) are the ratios of the decay constants (lifetimes) of $Ξ_{bc}^{0}$ and $Λ_b^{0}$. The branching ratio of $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$ is related to that of $Λ_c^+\to Δ^{++} K^-$, and thereby a conjectured topology analysis leads to the range for the branching ratio as: ${\cal BR}(Ξ_{cc}^+\to Σ_{c}^{++}(2520) K^-)\in \left[0.36\%,1.80\%\right]$. The decay $Ξ_{cc}^+\to Σ_{c}^{++}(2520) K^-$ would be reconstructed in the $ Λ_{c}^{+}K^{-}π^{+}$ final state which is easy to access even at a hadron collider. Based on the two facts that abundant heavy quarks can be produced at a hadron collider like LHC, and the branching ratios of $Ξ_{bc}^{0}\to pK^{-}$ and $Ξ_{cc}^{+}\to Σ_{c}^{++}(2520)K^{-}$ are sizable, we urge our experimental colleagues to perform a search at LHCb. This will presumably lead to the discovery of the $Ξ_{bc}$ and $Ξ_{cc}^{+}$ , and precision measurements of the branching ratios in the future are helpful to investigate their decay mechanism.

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arXiv2016

Nonleptonic decays of $B \to ( f_1(1285),f_1(1420) ) V$ in the perturbative QCD approach

We investigate the branching ratios, the polarization fractions, the direct CP-violating asymmetries, and the relative phases in 20 nonleptonic decay modes of $B \to f_1 V$ within the framework of perturbative QCD approach at leading order with $f_1$ including two $^3\!P_1$-axial-vector states $f_1(1285)$ and $f_1(1420)$. Here, $B$ denotes $B^+$, $B^0$, and $B_s^0$ mesons and $V$ stands for the lightest vector mesons $ρ$, $K^*$, $ω$, and $ϕ$ , respectively. The $B_s^0 \to f_1 V$ decays are studied theoretically for the first time in the literature. Together with the angle $ϕ_{f_1} \approx (24^{+3.2}_{-2.7})^\circ$ extracted from the measurement through $B_{d/s} \to J/ψf_1(1285)$ modes for the $f_1(1285)-f_1(1420)$ mixing system, it is of great interest to find phenomenologically some modes such as the tree-dominated $B^+ \to f_1 ρ^+$ and the penguin-dominated $B^{+,0} \to f_1 K^{*+,0}, B_s^0 \to f_1 ϕ$ with large branching ratios around ${\cal O}(10^{-6})$ or even ${\cal O}(10^{-5})$, which are expected measurable at the LHCb and/or the Belle-II experiments in the near future. The good agreement [sharp contrast] of branching ratios and decay pattern for $B^+ \to f_1 ρ^+, B^{+,0} \to f_1(1285) K^{*+,0} [B^{+,0} \to f_1(1420) K^{*+,0}]$ decays between QCD factorization and perturbative QCD factorization predictions can help us to distinguish these two rather different factorization approaches via precision measurements, which would also be helpful for us to explore the annihilation decay mechanism through its important roles for the considered $B \to f_1 V$ decays.

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arXiv2016

Two-body charmed B(Bs) decays involving a light scalar meson

Based on the assumption of two-quark structure for the light scalar mesons, within the framework of perturbative QCD approach, we investigate the $B_{q}\to D_{(s)}^{(*)} S(q=u,d,s)$ decays induced by $b\to u $ transition, where $S$ denotes a light scalar meson. Under two different scenarios, we calculate the branching ratios of 96 decay modes totally, which are in the range of $10^{-5}$ to $10^{-8}$. The comparison between our predictions and the experimental data will allow us to probe the inner structure of the scalar mesons. In the standard model, since all decays can only occur through tree operators, there are no $CP$ asymmetries. From our calculations, it has been shown that the annihilation type diagrams, especially the nonfactorizable annihilation diagrams, play important roles in the decay amplitudes, especially for these color-suppressed and pure annihilation type decay modes. We also find that the branching ratios of color-allowed type decays are sensitive to the different scenarios, so the measurements of them will be ideal places to differentiate the different scenarios. It can be found that the ratios between $Br(B^0\to D^{(*)0}σ)$ and $Br(B^0\to D^{(*)0}f_0)$, and between $Br(B^+\to D^{(*)+}σ)$ and $Br(B^{+}\to D^{(*)+}f_0)$ can be used to determine the mixing angle of $σ$ and $f_0$.

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arXiv2015

Constrain the UT angle $γ$ by CP violation parameters in $B^0 \to π^+ π^-$

We calculate the tree and penguin amplitudes in the $B^0\toπ^+π^-$ decay channel employing the perturbative QCD factorization approach. Using the amplitudes as input with the theoretical uncertainties sufficiently considered, we constrain the UT angle $γ$ to $53^\circ\leqγ\leq70^\circ$, from the measurements of the CP violation parameters $C_{π^+π^-}$ and $S_{π^+π^-}$ in $B^0\toπ^+π^-$. The U-spin breaking effect between $B^0\toπ^+π^-$ and $B_s^0\to K^+K^-$ is estimated to be around 30\%.

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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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arXiv2015

S-wave ground state charmonium decays of $B_c$ mesons in the perturbative QCD approach

We make a systematic investigation on the two-body nonleptonic decays $B_c\rightarrow J/Ψ(η_c),M$ by employing the perturbative QCD approach based on $k_T$ factorization, where $M$ is a light pseudoscalar or vector or a heavy charmed meson. We predict the branching ratios and direct CP asymmetries of these $B_c$ decays and also the transverse polarization fractions of $B_c\rightarrow J/ΨV,J/ψD^{*}_{(s)}$ decays. It is found that these decays have a large branching ratios of the order of $10^{-4} - 10^{-2}$ and could be measured by the future LHC-b experiment. Our predictions for the ratios of branching fractions $\frac{\mathcal {BR}(B_c^+\rightarrow J/ΨD_s^+)} {\mathcal {BR}(B_c^+\rightarrow J/Ψπ^+)}$ ,$\frac{\mathcal {BR}(B_c^+\rightarrow J/ΨD_s^{*+})} {\mathcal {BR}(B_c^+\rightarrow J/ΨD_s^+)}$ and $\frac{\mathcal {BR}(B_c^+\rightarrow J/ΨK^+)} {\mathcal {BR}(B_c^+\rightarrow J/Ψπ^+)}$ are in good agreement with the data. A large transverse polarization fraction which can reach $48\%$ is predicted in $B_c^+\rightarrow J/ΨD_s^{*+}$ decay, which is consistent with the data. We find a possible direct CP violation in $B_c\rightarrow J/ψD^{*}$ decays, which are helpful to test the CP violating effects in $B_c$ decays.

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arXiv2014

Charmless hadronic $B \to (f_1(1285),f_1(1420)) P$ decays in the perturbative QCD approach

We study 20 charmless hadronic $B \to f_1 P$ decays in the perturbative QCD(pQCD) formalism with $f_1$ representing axial-vector mesons $f_1(1285)$ and $f_1(1420)$ that result from a mixing of quark-flavor $f_{1q}$ and $f_{1s}$ states with the angle $ϕ_{f_1}$. The estimations of branching ratios and CP asymmetries of the considered $B \to f_1 P$ decays are presented in the pQCD approach with $ϕ_{f_1} \sim 24^\circ$ from recently measured $B_{d/s} \to J/ψf_1(1285)$ decays. It is found that (a) the tree(penguin) dominant $B^+ \to f_1 π^+(K^+)$ decays with large branching ratios[${\cal O}(10^{-6})$] and large direct CP violations(around 14% $\sim$ 28% in magnitude) simultaneously are believed to be clearly measurable at the LHCb and Belle II experiments; (b) the $B_d \to f_1 K_S^0$ and $B_s \to f_1 (η, η^{\prime})$ decays with nearly pure penguin contributions and safely negligible tree pollution also have large decay rates in the order of $10^{-6} \sim 10^{-5}$, which can be confronted with the experimental measurements in the near future; (c) as the alternative channels, the $B^+ \to f_1 (π^+, K^+)$ and $B_d \to f_1 K_S^0$ decays have the supplementary power in providing more effective constraints on the Cabibbo-Kobayashi-Maskawa weak phases $α$, $γ$, and $β$ correspondingly, which are explicitly analyzed through the large decay rates and the direct and mixing-induced CP asymmetries in the pQCD approach and are expected to be stringently examined by the measurements with high precision. The complete abstraction can be found in the paper.

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arXiv2014

Penguin-dominated $B \to ϕK_1(1270)$ and $ϕK_1(1400)$ decays in the perturbative QCD approach

We investigate the CP-averaged branching ratios, the polarization fractions, the relative phases, and the CP-violating asymmetries of the penguin-dominated $B \to ϕK_1(1270) $ and $ ϕK_1(1400)$ decays in the perturbative QCD(pQCD) approach, where $K_1(1270)$ and $K_1(1400)$ are believed to be the mixtures of two distinct types of axial-vector $K_{1A}(^3P_1)$ and $K_{1B}(^1P_1)$ states with different behavior, however, their mixing angle $θ_{K_1}$ is still a hot and controversial topic presently. By numerical evaluations with two different mixing angles $θ_{K_1} \sim 33^\circ$ and $58^\circ$ and phenomenological analysis, we find that: (a) the pQCD predictions for the branching ratio, the longitudinal polarization fraction and the direct CP violation of $B^\pm \to ϕK_1(1270)^\pm$ decay with the smaller angle $33^\circ$ are in good agreement with the currently available data; (b) though the central values significantly exceed the available upper limit, both pQCD predictions of $Br(B^\pm \to ϕK_1(1400)^\pm)$ with two different mixing angles are consistent with that obtained in QCD factorization and with the preliminary data in 2$σ$ errors. These results and other relevant predictions for the considered decays will be further tested by the LHCb and the forthcoming Super-B experiments; (c) the weak annihilation contributions can play an important role in $B \to ϕK_1(1270)$ and $ϕK_1(1400)$ decays; (d) these pQCD predictions combined with the future precision measurements can examine the reliability of the factorization approach employed here, but also explore the complicated QCD dynamics and mixing angle $θ_{K_1}$ of the axial-vector $K_1(1270)$ and $K_1(1400)$ system.

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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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arXiv2014

Perturbative QCD study of $B_s$ decays to a pseudoscalar meson and a tensor meson

We study two-body hadronic $B_s\to PT$ decays, with $P (T)$ being a light pseudoscalar (tensor) meson, in the perturbative QCD approach. The CP-averaged branching ratios and the direct CP asymmetries of the $ΔS=0$ modes are predicted, where $ΔS$ is the difference between the strange numbers of final and initial states. We also define and calculate experimental observables for the $ΔS=1$ modes under the $B_s^0-\bar{B}_s^0$ mixing, including CP averaged branching ratios, time-integrated CP asymmetries, and the CP observables $C_{f}$, $D_{f}$ and $S_{f}$. Results are compared to the $B_s\to PV$ ones in the literature, and to the $B\to PT$ ones, which indicate considerable U-spin symmetry breaking. Our work provides theoretical predictions for the $B_s\to PT$ decays for the first time, some of which will be potentially measurable at future experiments.

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arXiv2013

Branching Ratios and CP Violations of B \to K_0^(1430) K^ Decays in the pQCD Approach

We investigate $B \to K_0^*(1430) K^*$ decays in the perturbative QCD(pQCD) factorization approach, where $B$ denotes $B_u$, $B_d$ and $B_s$ meson respectively, and the scalar $K_0^*(1430)$ is considered as a meson based on the model of conventional two-quark structure. With the light-cone distribution amplitude of $K_0^*(1430)$ defined in two scenarios, namely Scenario 1 and Scenario 2, we make the first estimation for the branching ratios and CP-violating asymmetries for those concerned decay modes in the pQCD factorization approach. For all considered $B \to K_0^*(1430) K^*$ decays in this paper, only one preliminary upper limit on the branching ratio of $B^0 \to {K_0^*(1430)}^0 \bar{K}^{*0}$ measured at 90% C.L. by Belle Collaboration is available now. It is therefore of great interest to examine the predicted physical quantities at two $B$ factories, Large Hadron Collider experiments, and forthcoming Super-$B$ facility, then test the reliability of the pQCD approach employed to study the considered decay modes involving a $p$-wave scalar meson as one of the final state mesons. Furthermore, these pQCD predictions combined with the future precision measurements are also helpful to explore the complicated QCD dynamics involved in the light scalars.

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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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arXiv2013

Pure annihilation type $ D\to PP(V)$ decays in the perturbative QCD approach

The annihilation type diagrams are difficult to calculate in any kind of models or method. Encouraged by the the successful calculation of pure annihilation type B decays in the perturbative QCD factorization approach, we calculate the pure annihilation type $D\to PP(V)$ decays in the perturbative QCD approach based on the $k_T$ factorization. Although the expansion parameter $1/m_D$ is not very small, our leading order numerical results agree with the existing experiment data for most channels. We expect the more accurate observation from experiments, which can help us learn about the dynamics of $D$ meson weak decays.

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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

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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