arXiv subjects

Zhen-Jun Xiao

Publications and source records attributed to Zhen-Jun Xiao.

At least 55 records · Page 3Linked to original sources

arXiv2019

Phenomenological studies on the $B_{d,s}^0 \to J/ψf_0(500) [f_0(980)]$ decays

Encouraged by the global agreement between theoretical predictions and experimental measurements for $B \to J/ψV$ decays, we extend that perturbative QCD formalism to $B_{d,s}^0 \to J/ψf_0(500) [f_0(980)]$ decays at the presently known next-to-leading order in the quark-antiquark description of $f_0(500)$ and $f_0(980)$. With the angle $ϕ_f \approx 25^\circ$ of the $f_0(500)-f_0(980)$ mixing in the quark-flavor basis, we find that the branching ratios of the $B_d^0 \to J/ψf_0(500) (\to π^+ π^-)$ and $B_{d,s}^0 \to J/ψf_0(980) (\to π^+ π^-)$ modes generally agree with the current data or the upper limits within uncertainties, except for the seemingly challenging $B_s^0 \to J/ψf_0(500) (\to π^+π^-)$ one. Then, we further explore the relevant observables of the $B_{d,s}^0 \to J/ψf_0(500) [f_0(980)]$ decays, which could provide further constraints on the mixing angle $ϕ_f$ and/or SU(3) flavor symmetry breaking effects. As a byproduct, we predict ${\rm BR}(B_{d}^0 \to J/ψf_0(980)(\to K^+ K^-))=5.8^{+3.1}_{-2.9} \times 10^{-7}$ and ${\rm BR}(B_{s}^0 \to J/ψf_0(980)(\to K^+ K^-)) =4.6^{+2.6}_{-2.3} \times 10^{-5}$. All theoretical predictions await the future examinations with high precision.

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arXiv2019

Quasi-two-body decays $B \to D K^*(892) \to D K π$ in the perturbative QCD approach

We study the quasi-two-body decays $B\to D K^*(892) \to D Kπ$ by employing the perturbative QCD approach. The two-meson distribution amplitudes $Φ_{Kπ}^{\text{$P$-wave}}$ are adopted to describe the final state interactions of the kaon-pion pair in the resonance region. The resonance line shape for the $P$-wave $Kπ$ component $K^*(892)$ in the time-like form factor $F_{Kπ}(s)$ is parameterized by the relativistic Breit-Wigner function. For most considered decay modes, the theoretical predictions for their branching ratios are consistent with currently available experimental measurements within errors. We also disscuss some ratios of the branching fractions of the concerned decay processes. More precise data from LHCb and Belle-II are expected to test our predictions.

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arXiv2019

The next-to-leading order corrections to rho meson electromagnetic form factors in the $k_T$ factorization approach

In this paper we calculate the next-to-leading-order (NLO) corrections to $ρ$-meson electromagnetic form factors by employing the $k_T$ factorization approach. We find that the NLO correction to $F_i (Q^2)(i=LT,TL)$ is around $30\%$ of the leading-order (LO) contributionin the region $Q^2>2GeV^2$. The NLO correction to $F_{LL}(Q^2)$ is close to $20\%$ of the LO one in the region $Q^2>3GeV^2$. The NLO radiative corrections to the electric, magnetic, and quadruple form factors $F_j(Q^2) (j=1,2,3)$ are sizeable in magnitude and agree with those from other approaches.

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arXiv2019

Quasi-two-body decays $B_{(s)}\to K^*(892)h\to Kπh$ in perturbative QCD approach

We extend our recent works on the $P$-wave two-pion resonant contributions to the kaon-pion cases in the hadronic charmless $B$ meson decays by employing the perturbative QCD approach. The concerned decay modes are analysed in the quasi-two-body framework by parameterizing the kaon-pion distribution amplitude $Φ_{K π}^{\rm P}$, which contains the final state interactions between the kaon and pion in the resonant region. The relativistic Breit-Wigner formula for the $P$-wave resonant state $K^*(892)$ is adopted to parameterize the time-like form factor $F_{Kπ}$. We calculate the $CP$-averaged branching ratios and direct $CP$-violating asymmetries of the quasi-two-body decays $B_{(s)}\to K^*(892) h\to Kπh$, with $h=(π, K)$, in this work. It is shown that the agreement of theoretical results with the experimental data can be achieved, through which Gegenbauer moments of the $P$-wave kaon-pion distribution amplitudes are determined. The predictions in this work will be tested by the precise data from the LHCb and the future Belle II experiments.

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arXiv2018

Form factors for semileptonic $B_{c}$ decays into $η^{(')}$ and Glueball

We calculated the form factors of $B_{c}$ transitions into $η^{(')}$ meson and pseudoscalar Glueball, where the $B_{c}$ meson is a bound state of two different heavy flavors and is treated as a nonrelativistic state, while the mesons $η^{(')}$ and Glueball are treated as light-cone objects since their masses are smaller enough compared to the transition momentum scale. The mechanism of two gluon scattering into $η^{(')}$ dominated the form factors of $B_{c}$ decays into $η^{(')}$. We considered the $η-η'-$Glueball mixing effect, and then obtained their influences on the form factors. The form factors of $B_{c}$ transitions into $η^{(')}$ and pseudoscalar Glueball in the maximum momentum recoil point were obtained as follows: $f^η_{0,+}(q^2=0)=1.38^{+0.00}_{-0.02}\times 10^{-3}$,$f^{η'}_{0,+}(q^2=0)=0.89^{+0.11}_{-0.10}\times 10^{-2}$ and $f^{G}_{0,+}(q^2=0)=0.44^{+0.13}_{-0.05}\times 10^{-2}$. Also phenomenological discussions for semileptonic $B_{c}\toη^{(')}+\ell+\barν_\ell$, $B_{c}\to G(0^{-+})+\ell+\barν_\ell$ and $D_{s}\to η+\ell+\barν_\ell$ decays are given.

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arXiv2018

Improved perturbative QCD formalism for $B_c$ meson decays

We derive the $k_T$ resummation for doubly heavy-flavored $B_c$ meson decays by including the charm quark mass effect into the known formula for a heavy-light system. The resultant Sudakov factor is employed in the perutrbative QCD study of the "golden channel" $B_c^+ \to J/ψπ^+$. With a reasonable model for the $B_c$ meson distribution amplitude, which maintains approximate on-shell conditions of both the partonic bottom and charm quarks, it is observed that the imaginary piece of the $B_c \to J/ψ$ transition form factor appears to be power suppressed, and the $B_c^+ \to J/ψπ^+$ branching ratio is not lower than $10^{-3}$. The above improved perutrbative QCD formalism is applicable to $B_c$ meson decays to other charmonia and charmed mesons.

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arXiv2018

The next-to-leading order corrections to $B \to ρ$ transition in the $k_T$ factorization

In this paper, we investigate the factorization hypothesis step by step for the exclusive process $B \to ρ$ at next-to-leading order (NLO) with the collinear factorization approach, and then we extend our results to the $k_T$ factorization frame. We show that the soft divergence from the specific NLO diagrams will cancel each other at the quark level, while the remaining collinear divergence can be absorbed into the NLO wave functions. The full NLO amplitudes can be factorized into two parts: the NLO $B$ and $ρ$ meson wave functions containing the collinear divergence and the leading order (LO) finite hard kernels. We give the general form of the nonlocal hadron matrix for the NLO $B$ and $ρ$ meson wave functions and all results of factorization for different twists' combinations.

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arXiv2018

Quasi-two-body decays $B_{(s)}\to P f_2(1270)\to Pππ$ in the perturbative QCD approach

In this work, we calculate the $CP$-averaged branching ratios and direct $CP$-violating asymmetries of the quasi-two-body decays $B_{(s)}\to P f_2(1270)\to Pππ$ with the two-pion distribution amplitude $Φ_{ππ}^{\rm D}$ by using the perturbative QCD factorization approach, where $P$ represents a light pseudoscalar meson $K, π, η$ and $η^{\prime}$. The relativistic Breit-Wigner formula for the $D$-wave resonance $f_2(1270)$ is adopted to parameterize the timelike form factor $F_π$, which contains the final state interactions between the pions in the resonant regions. The consistency of theoretical results with data can be achieved by determining the Gegenbauer moments of the $D$-wave two-pion distribution amplitudes. The decay rates for the considered decay modes are generally in the order of $10^{-9}$ to $ 10^{-6}$. The integrated direct $CP$ asymmetries for the charged modes agree with the {\it BABAR} and Belle measurements. As a by-product, we extract the branching ratios of $B_{(s)}\to Pf_2(1270)$ from the corresponding quasi-two-body decay modes, which still need experimental tests at the ongoing and forthcoming experiments.

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arXiv2018

Weak decays of $B_c$ into two hadrons under flavor SU(3) symmetry

A large number of $B_c$ meson events have been recorded at the LHCb detector, especially some two-body hadronic decay modes. We analyzed the weak decays of the $B_c$ meson into two hadron states under the flavor SU(3) symmetry. The relations among amplitudes of $B_c$ into $ D+P(V)$, $B+P(V)$, $P(V)+P(V)$, $T_8+\bar T_8$ and $T_{10}+\bar T_{10}$ were investigated systematically, where $P$ ( $V$) denotes a light pseudoscalar (vector) meson and $T_{8,10}$ denotes a light baryon. The $η-η'$ mixing and $ω-ϕ$ mixing effects are also considered for the phenomenological discussions. We obtained the relations among decay widths of different $B_c$ decay channels. These results are helpful to study the two-body decay properties of the $B_c$ meson and test the flavor SU(3) symmetry.

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arXiv2018

Anatomy of $B_s \to VV $ decays and effects of next-to-leading order contributions in the perturbative QCD factorization approach

By employing the perturbative QCD (PQCD) factorization approach, we calculated the branching ratios, CP-violating asymmetries, the longitudinal and transverse polarization fractions and other physical observables of the thirteen charmless hadronic $\bar{B}^0_s \to V V $ decays with the inclusion of all currently known next-to-leading order (NLO) contributions. We focused on the examination of the effects of all those currently known NLO contributions and found that: (a) for the measured decays $\bar{ B}_s^0 \to ϕϕ, K^{*0} ϕ,\bar K^{*0} K^{*0}$ and $ρ^0 ϕ$, the NLO contributions can provide $\sim 20\%$ to $\sim 40\%$ enhancements to the leading order (LO) PQCD predictions of their CP-averaged branching ratios, and consequently the agreement between the PQCD predictions and the measured values are improved effectively after the inclusion of the NLO contributions; (b) for the measured decays, the NLO corrections to the LO PQCD predictions for $(f_L,f_\perp)$ and $(ϕ_{\|},ϕ_{\bot})$ are generally small in size, but the weak penguin annihilation contributions play an important role in understanding the data about their decay rates, $f_L$ and $f_\perp$; (c) the NLO PQCD predictions for above mentioned physical observables do agree with the measured ones and the theoretical predictions from the QCDF, SCET and FAT approaches; (d) for other considered $B_s^0 \to VV$ decays, the NLO PQCD predictions for their decay rates and other physical observables are also basically consistent with the theoretical predictions from other popular approaches, future precision measurements could help us to test or examine these predictions.

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arXiv2018

Rho-pion transition form factors in the $k_T$ factorization formulism revisited

We revisit the evaluations for the spacelike and timelike $ρπ$ transition form factors $F_{ρπ}(Q^2)$ and $G_{ρπ}(Q^2)$ with the inclusion of the the next-to-leading order (NLO) QCD contributions in the framework of the $k_T$ factorization theorem. The infrared divergence is regularized by the transversal momentum carried by external valence quarks, and ultimately absorbed into the meson wave functions. In the region of $ Q^2 \leqslant 2 \, \textrm{GeV}^2 $, where PQCD factorization apporach applicable, the NLO contribution can bring no larger than $ 35\%$ enhancement to the spacelike form factor $F_{ρπ}(Q^2)$. For the timelike form factor derived under the kinematic exchanging symmetry, this contribution is also under control when the momentum transfer squared is large enough. We also prolong our prediction into the small $Q^2$ region by taking the Lattice QCD results into account, and subsequently obtain the coupling $g_{ρπγ} = G_{ρπ}(0)=0.596$.

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arXiv2018

Anatomy of $B_s \to PV $ decays and effects of next-to-leading order contributions in the perturbative QCD factorization approach

In this paper, we will make systematic calculations for the branching ratios and the CP-violating asymmetries of the twenty one $\bar{B}^0_s \to PV $ decays by employing the perturbative QCD (PQCD) factorization approach. Besides the full leading-order (LO) contributions, all currently known next-to-leading order (NLO) contributions are taken into account. We found numerically that: (a) the NLO contributions can provide $\sim 40\%$ enhancement to the LO PQCD predictions for ${\cal B}(\bar{B}_s^0 \to K^0 \bar{K}^{*0})$ and $ {\cal B}(\bar{B}_s^0 \to K^{\pm}K^{*\mp})$, or a $\sim 37\% $ reduction to $ \calb(\bar{B}_s^0 \to π^{-} K^{*+})$, and we confirmed that the inclusion of the known NLO contributions can improve significantly the agreement between the theory and those currently available experimental measurements, (b) the total effects on the PQCD predictions for the relevant $B\to P$ transition form factors after the inclusion of the NLO twist-2 and twist-3 contributions is generally small in magnitude: less than $ 10\%$ enhancement respect to the leading order result, (c) for the "tree" dominated decay $\bar B_s^0\to K^+ ρ^- $ and the "color-suppressed-tree" decay $\bar B_s^0\to π^0 K^{*0}$, the big difference between the PQCD predictions for their branching ratios are induced by different topological structure and by interference effects among the decay amplitude ${\cal A}_{T,C}$ and ${\cal A}_P$: constructive for the first decay but destructive for the second one, and (d) for $\bar{B}_s^0 \to V(η, \etar)$ decays, the complex pattern of the PQCD predictions for their branching ratios can be understood by rather different topological structures and the interference effects between the decay amplitude $\cala(Vη_q)$ and $\cala(Vη_s)$ due to the $η-\etar$ mixing.

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arXiv2017

Quasi-two-body decays $B_c \to D_{(s)} [ρ(770),ρ(1450),ρ(1700) \to ] ππ$ in the perturbative QCD factorization approach

In this paper, we studied the quasi-two-body $B_c \to D_{(s)} [ ρ(770),ρ(1450),ρ(1700) \to ] ππ$ decays by employing the perturbative QCD (PQCD) factorization approach. The two-pion distribution amplitudes $Φ_{ππ}$ are applied to include the final-state interactions between the pion pair, while the time-like form factors $F_π(w^2)$ associated with the $P$-wave resonant states $ρ(770)$, $ρ(1450)$ and $ρ(1700)$ are extracted from the experimental data of the $e^+e^-$ annihilation. We found that: (a) the PQCD predictions for the branching ratios of the quasi-two-body $B_c \to D_{(s)} [ρ(770), ρ(1450), ρ(1700) \to ] ππ$ decays are in the order of $10^{-9}$ to $ 10^{-5}$ and the direct $CP$ violations around $(10-40)\%$ in magnitude; (b) the two sets of the large hierarchy $R_{1a,1b,1c}$ and $R_{2a,2b,2c}$ for the ratios of the branching ratios of the considered decays are defined and can be understood in the PQCD factorization approach, while the self-consistency between the quasi-two-body and two-body framework for $B_{c} \to D_{(s)} [ρ(770) \to ] ππ$ and $B_{c} \to D_{(s)} ρ(770)$ decays are confirmed by our numerical results; (c) taking currently known ${\cal B}(ρ(1450)\toππ)$ and ${\cal B}(ρ(1700) \to ππ)$ as input, we extracted the theoretical predictions for ${\cal B}(B_{c} \to D ρ(1450)) $ and ${\cal B}(B_{c} \to D ρ(1700))$ from the PQCD predictions for the decay rates of the quasi-two-body decays $B_{c} \to D [ρ(1450), ρ(1700) \to ] ππ$. All the PQCD predictions will be tested in the future experiments.

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arXiv2017

Quasi-two-body decays $B_{(s)} \to D (ρ(1450),ρ(1700)) \to D ππ$ in the perturbative QCD factorization approach

By employing a framework for the quasi-two-body decays in the perturbative QCD (PQCD) factorization approach, we calculate the branching ratios of the decays $B_{(s)} \to D (ρ(1450),ρ(1700))\to D ππ$ with $D=(D_{(s)}, \bar{D}_{(s)})$. The pion vector form factor $F_π$, acquired from a {\it BABAR} Collaboration analysis of $e^+ e^- \to π^+ π^-(γ)$ data, is involved in the two-pion distribution amplitudes $Φ^{I=1}_{ππ}$. The PQCD predictions for the branching ratios of the considered quasi-two-body decays are in the range of $10^{-10} \sim 10^{-4}$. The PQCD predictions for ${\cal B}(B^0\to \bar{D}^0 (ρ^0(1450),ρ^0(1700)) \to \bar{D}^0 π^+π^-)$ agree well with the measured values as reported by LHCb if one takes still large theoretical errors into account. Unlike the traditional way of the PQCD approach, one can extract the decay rates for the two-body decays $B_{(s)} \to D (ρ(1450),ρ(1700))$ from the results of the corresponding quasi-two-body decays. The PQCD predictions for ${\cal B}(B_{(s)} \to D ρ(1450))$ and ${\cal B}(B_{(s)} \to D ρ(770))$ are similar in magnitude: an interesting relation to be tested by future experimental measurements.

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arXiv2017

Quasi-two-body decays $B \to η_c {(1S ,2S)}\;[ρ(770),ρ(1450),ρ(1700) \to ]\; ππ$ in the perturbative QCD approach

In this paper, we calculated the branching ratios of the quasi-two-body decays $B \to η_c (1S ,2S)$ $[ρ(770), ρ(1450),ρ(1700)\to ] ππ$ by employing the perturbative QCD (PQCD) approach. The contributions from the $P$-wave resonances $ρ(770)$, $ρ(1450)$ and $ρ(1700)$ were taken into account. The two-pion distribution amplitude $Φ_{ππ}^{\rm P}$ is parameterized by the vector current time-like form factor $F_π$ to study the considered decay modes. We found that (a) the PQCD predictions for the branching ratios of the considered quasi-two-body decays are in the order of $10^{-7} \sim 10^{-6}$, while the two-body decay rates ${\cal B}(B \to η_c{(1S,2S)} (ρ(1450),ρ(1700)))$ are extracted from those for the corresponding quasi-two-body decays; (b) the whole pattern of the pion form factor-squared $|F_π|^2$ measured by the BABAR Collaboration could be understood based on our theoretical results; (c) the general expectation based on the similarity between $B \to η_c ππ$ and $B \to J/ψππ$ decays are confirmed: $R_2(η_c)\approx 0.45$ is consistent with the measured $R_2(J/ψ)\approx 0.56\pm 0.09$ within errors; and (d) new ratios $R_3(η_c(1S))$ and $R_4(η_c(2S))$ among the branching ratios of the considered decay modes are defined and could be tested by future experiments.

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arXiv2017

Hadronic decays of $B \to a_1(1260) b_1(1235)$ in the perturbative QCD approach

We calculate the branching ratios and polarization fractions of the $B \to a_1 b_1$ decays in the perturbative QCD(pQCD) approach at leading order, where $a_1$($b_1$) stands for the axial-vector $a_1(1260)[b_1(1235)]$ state. By combining the phenomenological analyses with the perturbative calculations, we find the following results: (a) the large decay rates around $10^{-5}$ to $10^{-6}$ of the $B \to a_1 b_1$ decays dominated by the longitudinal polarization(except for the $B^+ \to b_1^+ a_1^0$ mode) are predicted and basically consistent with those in the QCD factorization(QCDF) within errors, which are expected to be tested by the Large Hadron Collider and Belle-II experiments. The large $B^0 \to a_1^0 b_1^0$ branching ratio could provide hints to help explore the mechanism of the color-suppressed decays. (b) the rather different QCD behaviors between the $a_1$ and $b_1$ mesons result in the destructive(constructive) contributions in the nonfactorizable spectator diagrams with $a_1(b_1)$ emission. Therefore, an interesting pattern of the branching ratios appears for the color-suppressed $B^0 \to a_1^0 a_1^0, a_1^0 b_1^0,$ and $b_1^0 b_1^0$ modes in the pQCD approach, $Br(B^0 \to b_1^0 b_1^0) > Br(B^0 \to a_1^0 b_1^0) \gtrsim Br(B^0 \to a_1^0 a_1^0)$, which is different from $Br(B^0 \to b_1^0 b_1^0) \sim Br(B^0 \to a_1^0 b_1^0) \gtrsim Br(B^0 \to a_1^0 a_1^0)$ in the QCDF and would be verified at future experiments. (c) the large naive factorization breaking effects are observed in these $B \to a_1 b_1$ decays. Specifically, the large nonfactorizable spectator(weak annihilation) amplitudes contribute to the $B^0 \to b_1^+ a_1^-(B^+ \to a_1^+ b_1^0\; {\rm and}\; B^+ \to b_1^+ a_1^0)$ mode(s), which demand confirmations via the precise measurements.

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arXiv2017

The quasi-two-body decays $B_{(s)} \to (D_{(s)},\bar{D}_{(s)}) ρ\to (D_{(s)}, \bar{D}_{(s)})ππ$ in the perturbative QCD factorization approach

In this paper, we studied the $B_{(s)} \to (D_{(s)},\bar{D}_{(s)}) ρ\to (D_{(s)}, \bar{D}_{(s)})ππ$ decays by employing a framework for the quasi-two-body decays in the perturbative QCD (PQCD) factorization approach. We use the two-pion distribution amplitudes $Φ_{ππ}$, which contains both resonant and nonresonant contributions from the pion pair, to describe the final state interactions (FSIs) between the pions in the resonant region. We found that (a) for all considered decays, the PQCD predictions for their branching ratios based on the quasi-two-body and the two-body framework agree well with each other due to ${\cal B}(ρ\to ππ) \approx 100\%$; For $B^+\to \bar{D^0}ρ^+\to \bar{D^0}π^+ π^0$ and other four considered decay modes, the PQCD predictions do agree well with the measured values within errors; (b) the great difference between the PQCD predictions for ${\cal B}(B\to \bar{D} ρ\to \bar{D} ππ)$ and ${\cal B}(B\to D ρ\to D ππ)$ can be understood by the strong CKM suppression factor $ R_{\rm CKM} \approx 3 \times 10^{-4}$; (c) for the $B_s\to D ρ\to D ππ$ and $B_s\to \bar{D} ρ\to \bar{D} ππ$ decays, however, the PQCD predictions of $R_{\rm s1}\approx 0.13$ and $R_{\rm s2}\approx 0.14$ do agree very well with the moderate CKM suppression factor $R^s_{\rm CKM}\approx 0.14$; and (d) the PQCD predictions for the ratios $R_{Dρ}$ and the strong phase difference $\cosδ_{Dρ}$ of the three $B \to \bar{D} ρ$ decay modes agree well with the LHCb measurements within one standard deviation.

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arXiv2017

Quasi-two-body decays $B_{(s)}\to Pρ^\prime(1450), Pρ^{\prime\prime}(1700)\to Pππ$ in the perturbative QCD approach

In this work, we calculate the $CP$-averaged branching ratios and direct $CP$-violating asymmetries of the quasi-two-body decays $B_{(s)}\to P ρ^\prime(1450), Pρ^{\prime\prime}(1700)\to P ππ$ by employing the perturbative QCD (PQCD) factorization approach, where $P$ is a light pseudoscalar meson $K, π, η$ and $η^{\prime}$. The considered decay modes are studied in the quasi-two-body framework by parameterizing the two-pion distribution amplitude $Φ_{ππ}^{\rm P}$. The $P$-wave time-like form factor $F_π$ in the resonant regions associated with the $ρ^\prime(1450)$ and $ρ^{\prime\prime}(1700)$ is estimated based on available experimental data. The PQCD predictions for the $CP$-averaged branching ratios of the decays $B_{(s)}\to Pρ^\prime(1450), Pρ^{\prime\prime}(1700)\to Pππ$ are in the order of $10^{-7} \sim 10^{-9}$. The branching ratios of the two-body decays $B_{(s)}\to Pρ^\prime(1450), Pρ^{\prime\prime}(1700)$ are extracted from the corresponding quasi-two-body decay modes. The whole pattern of the pion form factor-squared $|F_π|^2$ measured by {\it BABAR} Collaboration could also be understood based on our studies. Our PQCD predictions will be tested by the precise data from the LHCb and the future Belle II experiments.

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