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Zhi-Tian Zou

Publications and source records attributed to Zhi-Tian Zou.

At least 19 recordsLinked to original sources

Large CP violation in $Λ_b\rightarrow ΛD$ decays and extraction of the Cabibbo-Kobayashi-Maskawa angle $γ$

Motivated by the first observation of CP violation in $b$-baryon decays, the search for baryonic decays exhibiting large CP violation will be a primary focus in the coming years. We propose that significant CP-violating effects exist in the decay $Λ_b \to ΛD$, where $D$ denotes a CP eigenstate of the $D^0 - \bar{D}^0$ system. The predicted CP asymmetries for both the CP-even and CP-odd modes can reach magnitudes as large as $50\%$, making these decays promising targets for measurement at the LHCb experiment. Additionally, we predict for the first time several nonzero CP-violating observables associated with angular distribution parameters, providing valuable complementary information in the search for CP violation in baryon decays. Furthermore, we propose a novel strategy to extract the CKM angle $γ$ by combining data on angular distribution parameters and decay rates from the relevant channels. We emphasize that $Λ_b \rightarrow ΛD$ decays are among the most promising candidates for determining $γ$ in the baryon sector. Our findings may offer new insights for future theoretical and experimental investigations.

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Revisiting $\bar B^0 \rightarrow Λ_c^+ \bar p$ decay with higher twist corrections

We investigate the single-charmed baryonic decays $\bar B^0 \to Λ_c^+ \bar p$ and $\bar B^0 \to \barΛ_c^- p$, which receive contributions from both $W$-emission and $W$-exchange topologies, within the framework of perturbative QCD (PQCD). Higher-power corrections associated with the hadronic light-cone distribution amplitudes (LCDAs) of both the initial- and final-state hadrons are systematically taken into account. We find that these higher-twist contributions play an important role in baryonic $B$ decays and cannot be neglected. A sizable destructive interference between the $W$-emission and $W$-exchange amplitudes is observed, which significantly reduces the predicted branching fraction of $\bar B^0 \to Λ_c^+ \bar p$ and leads to improved agreement with experimental measurements. The doubly Cabibbo-suppressed decay $\bar B^0 \to \barΛ_c^- p$ is studied for the first time. Its branching fraction is predicted to be of order $10^{-8}$, placing it within the reach of future high-luminosity experiments. We further present the first theoretical predictions for the decay asymmetry parameters of both channels, which provide additional observables for testing the underlying decay dynamics and can be confronted with future experimental data.

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Semileptonic neutral current decays of $Ξ_b$ with dileptons or dineutrinos in the final state

We perform a detailed analysis of semileptonic $Ξ_b$ decays mediated by flavor-changing neutral currents ($b\to s$ and $b\to d$) with dilepton or dineutrino final states within the perturbative QCD framework. All independent form factors including vector, axial-vector, tensor, and pseudotensor currents are calculated and are used to analyze the decay branching fractions and angular distributions. Our numerical results for the branching fractions of $Ξ_b\to Ξ\ell^+\ell^-$ decays suggest they are within measurable reach for the LHCb experiment in the near future. Furthermore, we show that a measurement of the ratio $\mathcal{B}(Ξ_b^-\to Σ^- μ^+μ^-) / \mathcal{B}(Ξ_b^-\to Ξ^- μ^+μ^-)$ will allow for an independent determination of $|V_{td}/V_{ts}|$. For the case of unpolarized $Ξ_b$ baryons, we derive several angular observables, which can provide new and complementary constraints on Wilson coefficients in semileptonic FCNC transitions compared to those from mesonic decays. Finally, we present a combined analysis of dilepton and dineutrino channels, comparing various observables in detail. Our results offer further insights into the long-standing anomalies observed in $B$ meson decays.

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Quasi-two-body decays $B^+\to D_s^+ (R\to) K^+K^-$ in the perturbative QCD approach

A search for the decay $B^+\to D_s^+ K^+K^-$ has been reported by the LHCb Collaboration using $pp$ collision data corresponding to an integrated luminosity of $4.8\,\mathrm{fb}^{-1}$, collected at center-of-mass energies of 7, 8, and 13~TeV, in which no amplitude analysis of the $K^+K^-$ subsystem was performed. In this work, we study the resonant contributions to the decay $B^+\to D_s^+ K^+K^-$ within the perturbative QCD (PQCD) factorization framework. Contributions from the $S$-wave resonances $f_0(980)$, $f_0(1370)$, and $f_0(1500)$, the $P$-wave resonance $ϕ(1020)$, and the $D$-wave resonances $f_2(1270)$ and $f_2(1525)$ are taken into account. By introducing the corresponding two-meson distribution amplitudes for the $K^+K^-$ system, we perform a complete perturbative analysis of the quasi-two-body decays $B^+\to D_s^+(R\to)K^+K^-$, where $R$ denotes an intermediate resonance, and present the first PQCD predictions for the associated branching fractions. Using the narrow-width approximation, we further extract the branching fractions of the corresponding two-body decays $B^+\to D_s^+R$. Our results are consistent with the available experimental measurements and previous theoretical studies. Finally, we find that direct CP asymmetries vanish for these quasi-two-body decays within the Standard Model, so that any experimentally observed nonzero CP asymmetry would constitute a clear signal of physics beyond the Standard Model.

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Cabibbo-suppressed charged-current semileptonic decays of $Ξ_b$ baryons

We present the first perturbative QCD calculations of the $Ξ_b \to (Λ, Σ)$ transition form factors at leading order in $α_s$, which govern the Cabibbo-suppressed semileptonic decays $Ξ_b \to (Λ, Σ)\ell ν_\ell$ with $\ell = e, μ, τ$. Using these form factors, we evaluate differential and integrated branching fractions and angular observables within the helicity formalism. The branching ratios are predicted to be of order $10^{-4}$ for $Σ$ final states and $10^{-5}$ for $Λ$ final states, making them accessible to ongoing experiments such as LHCb. Ratios of decay rates between $τ$ and $e$ channels are also provided, offering new probes of lepton-flavor universality. Lepton-mass effects are found to significantly impact the integrated angular observables. Furthermore, a combined analysis of $b \to u$ and $b \to c$ transitions in $Ξ_b$ decays yields sub-percent precision for the ratios $\mathcal{R}_\ell(Σ/Ξ_c)$, enabling an independent determination of $|V_{ub}/V_{cb}|$ once the relevant decay-rate measurements become available.

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Branching ratios and CP asymmetries of $B^0 \to η_c f_0$ in the improved perturbative QCD formalism

Motivated by the idea of fragmented scalar glueball, we investigate the decays $B^0 \to η_c f_0$ within the improved perturbative QCD (iPQCD) framework by including the known next-to-leading order corrections. Here, $B^0$ and $f_0$ denote the neutral $B_{d,s}^0$ mesons and the light scalar mesons $f_0(500, 980, 1370, 1500)$ under the $q\bar q$ assignment. The CP-averaged branching ratios (BRs) and the CP asymmetries of $B^0 \to η_c f_0$ are evaluated with the $f_0(500)[f_0(1370)]-f_0(980)[f_0(1500)]$ mixing in quark-flavor basis. For effective comparisons with the near-future measurements, we further derive the $B^0 \to η_c f_0 (\to π^+ π^-/K^+ K^-)$ BRs under the narrow-width approximation. ${\rm BR}(B_s^0 \to η_c f_0(980) (\to π^+ π^-))= (2.87^{+1.38}_{-1.29}) \times 10^{-4}$ and ${\rm BR}(B_d^0 \to η_c f_0(500)(\to π^+π^-))/{\rm BR}(B_s^0 \to η_c f_0(980)(\to π^+π^-)) = (12^{+8}_{-7})\%$ obtained in the iPQCD formalism agree with the available measurements and/or predictions within uncertainties. Large BRs of $B_s^0 \to η_c f_0(1500) (\to π^+ π^-/K^+ K^-)$ and large direct CP asymmetries of $B^0 \to η_c f_0(1370, 1500)$ are accessible in the LHCb and Belle-II experiments. The experimental tests of these iPQCD predictions would help us to understand the nature of these light scalars more deeply and provide evidences to decipher $f_0(1500)$ as a primary or fragmented scalar glueball potentially.

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Correlated PQCD Analysis of the Semileptonic Decays $\overline{B}^0 \to D^{(*)+}\ell^-\barν_\ell$ and the Nonleptonic Decays $ \overline{B}^0 \to D^{(*)+}π^-$

We present a unified analysis of $\overline{B}^0 \to D^{(*)+}\ell^-\barν_\ell$ and $\overline{B}^0 \to D^{(*)+}π^-$ decays using the perturbative QCD (PQCD) approach. The $B \to D^{(*)}$ transition form factors are calculated at low $q^2$ and extrapolated to the high-$q^2$ region using the latest lattice QCD results via a model-independent $z$-expansion. This hybrid method provides a precise form factor description across the full kinematic range. We then predict the branching fractions and the lepton flavor universality ratios $R(D) = 0.336^{+0.014}_{-0.013}$ and $R(D^*) = 0.271^{+0.010}_{-0.010}$, which are consistent with the latest experimental averages. Furthermore, we perform a correlated study of the nonleptonic $ \overline{B}^0 \to D^{(*)+}π^-$ decays, calculating both factorizable and nonfactorizable amplitudes. To reduce hadronic uncertainties, we introduce and calculate the differential ratio $R^{(*)}_{π/\ell}(q^2)$, defined between nonleptonic and semileptonic decay rates, providing a sensitive test of factorization and possible new physics effects. The predictions presented here can be directly tested in ongoing Belle II and LHCb experiments.

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Investigation of $Λ_{b}\to Λ_{c} \ell^-\overlineν_\ell$ Decays in Perturbative QCD Approach

We investigate the semileptonic decays $Λ_{b} \to Λ_{c} \ell^- \barν_\ell$ (with $\ell = e, μ, τ$) within the framework of perturbative QCD (pQCD). The six independent $Λ_b \to Λ_c$ transition form factors are first calculated in the low-$q^2$ region using the $k_T$ factorization approach. These are then extrapolated to the full physical $q^2$ range via the model-independent $z$-expansion, incorporating recent lattice QCD results at high $q^2$. Based on the obtained form factors, we compute the branching fractions of $Λ_b \to Λ_c \ell^- \barν_\ell$ decays. Our prediction for the lepton flavor universality ratio, $\mathcal{R}_{Λ_c} = 0.29^{+0.12}_{-0.11}$, is slightly larger than the latest experimental measurement. In addition, we analyze several angular observables, including forward-backward asymmetries, lepton-side convexity parameters, and polarization asymmetries. These results offer valuable theoretical input for current and future experimental investigations of semileptonic heavy-to-heavy baryon transitions.

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Semileptonic baryon decays $Ξ_b\rightarrow Ξ_c \ell^- \barν_\ell $ in perturbative QCD

We perform a detailed analysis of the semileptonic $Ξ_b\rightarrow Ξ_c \ell^- \barν_\ell$ decays within the perturbative QCD framework. In our study, the $Ξ_b\rightarrow Ξ_c$ transition form factors are calculated using several popular models for baryonic light-cone distribution amplitudes. These form factors are then employed to analyze a range of observable quantities for the semileptonic processes via the helicity formalism. Our work presents predictions for the branching fractions of these decays for both the $τ$ and $e$ channels. Notably, the obtained lepton flavor universality ratio, $\mathcal{R}_{Ξ_c}\approx 0.3$, may offer new insights into the $\mathcal{R}^{(*)}$ puzzle. Furthermore, we investigate various angular observables, such as forward-backward asymmetries, lepton-side convexity parameters, and polarization asymmetries, which provide complementary information regarding potential new physics in $b$-baryonic semileptonic transitions. The numerical results for these angular observables are presented as both functions of $q^2$ and as averaged values. We observe that the lepton mass plays a significant role in shaping the angular distributions, affecting most of the observables under consideration. These results are expected to be valuable for both current and future experimental investigations of semileptonic heavy-to-heavy baryon decays.

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Enhanced Quark-Loop Contribution to Pure Annihilation Nonleptonic B-meson decays in PQCD approach

In this study, we conduct an enhanced investigation of pure annihilation-type charmless hadronic B-decays within the framework of the PQCD approach. Specifically, we account for the quark-loop enhanced contribution to various decay processes at the next-to-leading order(NLO) in the strong coupling constant $α_s$. The NLO amplitudes possess large imaginary parts that have signs opposite to those of the leading-order amplitudes. This cancellation effect implies that the NLO contribution does not significantly influence the branching ratios of the processes under consideration. However, the NLO effect explored in this work constitutes an important source of the strong phases in the weak - annihilation non-leptonic $\bar B_q$-meson decay amplitudes. As a result, it can have a substantial impact on CP - violating observables such as the direct CP asymmetry ${\cal A}_{\rm CP}^{\rm dir}$ and mixing induced CP asymmetry ${\cal A}_{\rm CP}^{\rm mix}$. The numerical result evidently revealed that NLO QCD correction significantly enhances both ${\cal A}_{\rm CP}^{\rm dir}$ and ${\cal A}_{\rm CP}^{\rm mix}$ of the pure annihilation type B decay processes.

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Systematic Analysis of $B_s \to SP$ Decays in Perturbative QCD Approach

Within the perturbative QCD (PQCD) framework, we present a systematic investigation of charmless $B_s \to SP$ decays, where $S$ and $P$ denote scalar and pseudoscalar mesons, respectively. By employing two distinct structural scenarios for scalar mesons, we calculate the branching fractions and direct $CP$ asymmetries for these processes. Our results reveal branching fractions ranging from $10^{-7}$ to $10^{-5}$, values that are well within the measurable range of current experiments. A striking contrast emerges between penguin- and tree-dominated decays: while penguin-dominated processes yield larger branching fractions, tree-dominated decays exhibit significantly enhanced direct $CP$ asymmetries. In particular, the decays $B_s \to f_0(1370) η$ and $B_s \to a_0(1450) K$ demonstrate marked sensitivity to the choice of scalar meson scenario, offering critical constraints for identifying the optimal model once experimental data are available. Furthermore, we calculate the branching fractions of $B_s \to f_0(980)(σ)P$ decays in two distinct ranges of the mixing angle of $f_0(980)-σ$. The dependencies of both branching fractions and $CP$ asymmetries on this mixing angle are rigorously analyzed, establishing a framework essential for determining its value with future experimental results. These findings provide a robust theoretical foundation for advancing the understanding of nonleptonic $B_s$decays in QCD-based formalisms, as well as the nature of scalar mesons.

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Quasi-Two-Body $B\to P (K^+K^-, π^+π^-)$ Decays with $f_0(980)$ Resonance

In this study, we investigate the $CP$-averaged branching fractions and direct $CP$ asymmetries in the quasi-two-body decays $B\to P (f_0(980) \to )(K^+K^-, π^+π^-)$ within the framework of perturbative QCD approach, where $P$ denotes light pseudoscalar mesons ($π$,$K$). The timelike form factor $F_{S}(ω)$, characterizing final-state interactions between collinear particles in the resonant region, is modeled through the revised relativistic Breit-Wigner formalism for the $S$-wave $f_0(980)$ resonance. Within the Gegenbauer moments of the $S$-wave two-meson distribution amplitudes constrained by current data, we predict the branching fractions of $B\to P (f_0(980) \to )(K^+K^-, π^+π^-)$ to lie in the range of $10^{-8}$ to $10^{-6}$. Our calculations reveal that our theoretical results for some decay modes exhibit satisfactory agreement with existing measurements from the BaBar and Belle collaborations. Furthermore, we extract the corresponding branching fractions of $B \to P f_0(980)$ decays from the quasi-two-body counterparts $B\to P (f_0(980) \to )π^+π^-$ rather than $B\to P (f_0(980) \to )K^+K^-$. All predictions are awaiting experimental verification in current and upcoming collider experiments.

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Higher twist corrections to doubly-charmed baryonic $B$ decays

Baryonic two-body $B$ mesons decays have been measured experimentally for some time, which provides an excellent ground for studying the QCD of baryonic $B$ decays. In this work, we investigate the two-body doubly-charmed baryonic $B$ decays in the perturbative QCD (PQCD) approach including higher twist contributions to the light-cone distribution amplitudes (LCDAs). The charmed baryon LCDAs are included up to the twist four and the effect of the subleading component of the $B$ meson LCDAs is studied for details. With the inclusion of these higher-power contributions, the PQCD results on rates can explain the current experimental data well. Moreover, we note that the SU(3) symmetry breaking is important in the concerned processes and play an essential role in understanding the measurements of $\mathcal{B}(\overline{B}^0\to Λ_c^+\overline Λ_c^-)$ and $ \mathcal{B}({B}^-\toΞ_c^0\overline Λ_c^-)$. We also evaluate the angular asymmetries for the first time, which have neither been measured experimentally nor calculated theoretically. All these predictions can be tested in future.

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Study of the $B^{+}\toπ^{+}\left(π^{+}π^{-}\right)$ decay in PQCD Approach

Based on the fitting results of the LHCb collaboration on the contributions of various intermediate resonances to the $B^{+}\toπ^{+}π^{+}π^{-}$ decay, we make systematically calculate the branching fractions and localized $CP$ asymmetries of the quasi-two-body $B^{+}\to π^{+} \left( ρ(770), ω(782), ρ(1450), f_{2}\left(1270\right)\to\right)π^{+}π^{-}$ decays within the perturbative QCD (PQCD) approach. Our theoretical predictions for the branching fractions agree well with the data within the errors. In order to further test the framework of the three-body $B$ decays in PQCD and the wave functions of $ππ$ pair, we also calculate the branching fractions of the corresponding two-body $B^{+}\toπ^{+}ρ(770)$, $B^{+}\toπ^{+}ω(782)$ and $B^{+}\toπ^{+}f_{2}\left(1270\right)$ decays under the narrow-width-approximation, which are in consistence with the experimental data. The direct $CP$ asymmetries of $B^{+}\toπ^{+}(ρ(770/1450)\to) π^{+}π^{-}$ decays are found to be very small because these decay modes are tree-dominated. However, due to the large penguin contributions from the chiral enhanced annihilation diagrams, $B^{+}\toπ^{+} (f_{2}\left(1270\right)\to )π^{+}π^{-}$ decay has a large direct $CP$ asymmetry, which is also discovered by LHCb collaboration. A relatively large $CP$ asymmetry is also expected in the $B^+\toπ^+ (ω\to)π^+π^-$ decay occurring via $ρ-ω$ mixing, which would be measured LHCb and Belle-II experiments in future.

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Charmonium decays of beauty baryons in the perturbative QCD approach

Motivated by recent advances in experimental measurements of heavy baryon decays, the charmonium decays of single $b$-baryon are investigated systematically in the framework of perturbative QCD approach. We calculate the decay branching ratios and helicity amplitudes as well as many pertinent decay asymmetry parameters that characterize the angular decay distributions. In particular, we estimate the fragmentation fractions of $b$ quark to $b$-baryons based on the current world averages of the branching ratio multiplied by fragmentation fraction. Some of the featured results are compared with the predictions of other approaches and experimental data. We also evaluate the branching ratios and angular asymmetries of the $Σ_b$ and $Ξ'_b$ decay modes, which have neither been measured experimentally nor calculated theoretically. Our results could be helpful for a future experimental search for them and provide deeper insights in the understanding of the dynamics of heavy-flavor weak decay processes.

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The $B^0 \to J/ψf_0(1370,1500,1710)$ decays: an opportunity for scalar glueball hunting

The scalars $f_0$ closest to 1.5 GeV contain the mesons $f_0(1370)$, $f_0(1500)$ and $f_0(1710)$, and the latter two ones are usually viewed as the potential candidates for the scalar glueballs. In this work, by including the important contributions from the vertex corrections, we study the decays $B^0 \to J/ψf_0$ within the improved perturbative QCD approach and analyze the possible scalar glueball hunting. Together with the two mixing models, namely, $f_0(1500) (f_0(1710))$ being the primary scalar glueball in model I (II), and two classification scenarios, namely, $f_0$ being the $q\bar q$ excited (ground) states in scenario 1 (2), the branching fractions associated with their ratios for $B^0 \to J/ψf_0$ are evaluated comprehensively. The predictions with still large uncertainties in the considered two mixing models are roughly consistent with currently limited data, which indicates that both more rich data and more precise predictions are urgently demanded to figure out the scalar glueball clearly in the future. Moreover, several interesting ratios between the branching fractions of $B^0 \to J/ψf_0(\to π^+ π^-/K^+ K^-)$ and $B^0 \to J/ψρ^0/ϕ(\to π^+ π^-/ K^+ K^-)$ that could help us to understand the nature of scalar $f_0$ are defined and predicted theoretically. These ratios should be examined in future experiments.

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Study of $B_s \to ϕ(ρ^0, ω)$ Decays in Standard Model and Family Non-universal $Z^\prime$ Model

Within QCD factorization approach, we employ the new results of form factors of $B_s \to ϕ$ and calculate the branching fractions, CP asymmetries (CPAs) and polarization fractions of the decay modes $B_s \to ϕ(ρ^0, ω)$ in both the standard model (SM) and the family non-universal $Z^\prime$ model. We find that in SM the above observables are relate to two parameters $ρ_H$ and $ϕ_H$, which characterize the end-point divergence in the hard spectator-scattering amplitudes. When setting $ρ_H=0.5$ and $ϕ_H\in [-180,180]^\circ$, the theoretical uncertainties are large. By combining the experimental data, our results can be used to constrain these two parameters. Supposing $ρ_H=0$, we study the effects of $Z^\prime$ boson on the concerned observables. With the available branching fraction of $B_s \to ϕρ^0$, the possible ranges of parameter spaces are obtained. Within the allowed parameter spaces, the branching fraction of $B_s \to ϕω$ can be enlarged remarkably. Furthermore, the new introduced weak phase plays important roles in significantly affecting the CPAs and polarization fractions, which are important observables for probing the effects of NP. If these decay modes were measured in the on-going LHC-b and Belle-II experiments in future, the peculiar deviation from SM could provide a signal of the family non-universal $Z^\prime$ model, which can also be used to constrain the mass of $Z^\prime$ boson in turn.

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Phenomenological analysis of the quasi-two-body $B \to D (R\to) K π$ decays in PQCD Approach

The quasi-two-body $B \to D (R\to) K π$ decays are calculated in PQCD approach based on the $k_T$ factorization by introducing the wave functions of $Kπ$ pair associated with the resonances $K^*(892)$, $K_0^*(1430)$ and $K_2^*(1430)$. The results show that most branching fractions are at the order of $10^{-7}$ or even smaller. However, for $B^0\to D^0(K^*\to)Kπ$ decays enhanced by the CKM element $V_{cs}$, their branching fractions are at the order of $10^{-6}$, which are measurable in the current ongoing experiments. Based on the narrow-width-approximation we also extract the branching fractions of the corresponding two-body $B \to D K^*$ decays and the results are in good agreement with previous predictions. Because these decays are only governed by the tree operators, there are no $CP$ asymmetries in these decays in the standard model.

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