arXiv subjects

Zhen-Jun Xiao

Publications and source records attributed to Zhen-Jun Xiao.

At least 109 records · Page 6Linked to original sources

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

Revisiting $Kπ$ puzzle in the pQCD factorization approach

In this paper, we calculated the branching ratios and direct CP violation of the four $B\to Kπ$ decays with the inclusion of all currently known next-to-leading order (NLO) contributions by employing the perturbative QCD (pQCD) factorization approach. We found that (a) Besides the 10% enhancement from the NLO vertex corrections, the quark-loops and magnetic penguins, the NLO contributions to the form factors can provide an additional $\sim 15%$ enhancement to the branching ratios, and lead to a very good agreement with the data; (b) The NLO pQCD predictions are $\acp^{dir}(B^0\to K^+π^-)=(-6.5\pm 3.1)%$ and $\acp^{dir}(B^+\to K^+ π^0)=(2.2\pm 2.0)%$, become well consistent with the data due to the inclusion of the NLO contributions.

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arXiv2013

Anatomy of $B \to K η^{(\prime)}$ decays in different mixing schemes and effects of next-to-leading order contributions in the perturbative QCD approach

In this paper we perform a comprehensive study of the four $B \to K \etap$ decays in the pQCD factorization approach. We calculate the CP-averaged branching ratios and CP-violating asymmetries of $B \to K\etap$ decays in the ordinary $η$-$\etar$, the $η$-$\etar$-$G$, and the $η$-$\etar$-$G$-$η_c$ mixing schemes. Besides the full LO contributions, all currently known NLO contributions to $B \to K \etap$ decays in the pQCD approach are taken into account. From our calculations and phenomenological analysis, we find the following. (a) The NLO contributions in general can provide significant enhancements to the LO pQCD predictions for the decay rates of the two $B \to K \etar$ decays, around $70%-89%$ in magnitude, but result in relatively small changes to $Br(B \to K η)$. (b) Although the NLO pQCD predictions in all three considered mixing schemes agree well with the data within one standard deviation, those pQCD predictions in the $η$-$\etar$-$G$ mixing scheme provide the best interpretation for the measured pattern of $Br(B \to K \etap)$: $Br(B^0 \to K^0 η) \approx 1.13\times 10^{-6}$, $Br(B^0 \to K^0 \etar) \approx 66.5 \times 10^{-6}$, $Br(B^\pm \to K^\pm η) \approx 2.36\times 10^{-6}$, and $Br(B^\pm \to K^\pm \etar) \approx 67.3 \times 10^{-6}$, which agree perfectly with the measured values. (c) The NLO pQCD predictions for the CP-violating asymmetries for the four considered decays are also in good consistent with the data. (d) The newly known NLO contribution to the relevant form factors $\calm_{FF}$ can produce about a 20% enhancement to the branching ratios $Br(B \to K \etar)$, which plays an important role in closing the gap between the pQCD predictions and the relevant data. (e) The general expectations about the relative strength of the LO and NLO contributions from different sources are examined and confirmed by explicit numerical calculations.

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arXiv2013

Semileptonic decays $B/B_s \to (η,\etar, G)(l^+l^-,l\barν,ν\barν)$ in the perturbative QCD approach beyond the leading order

In this paper we make a systematic study of the semileptonic decays $B/B_s \to (η,\etar, G)(l^+l^-,l\barν,ν\barν)$ by employing the perturbative QCD (pQCD) factorization approach. The next-to-leading-order (NLO) contributions to the relevant form factors are included, and the ordinary $η$-$\etar$ mixing scheme and the $η$-$\etar$-$G$ mixing scheme are considered separately, where $G$ denotes a pseudoscalar glueball. The numerical results and the phenomenological analysis indicate that (a) the NLO contributions to the relevant form factors provide 25% enhancement to the leading-order pQCD predictions for the branching ratios $Br(B^-\to η^{(')} l^-\barν_l)$, leading to a good agreement between the predictions and the data; (b) for all considered decays, the pQCD results are basically consistent with those from other different theoretical models; (c) the pQCD predictions in the two considered mixing schemes agree well with each other within theoretical errors. The outcomes presented here can be tested by LHCb and forthcoming Super-$B$ experiments.

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arXiv2013

Semileptonic decays $B_c\to(η_c,J/Ψ)lν$ in the perturbative QCD approach

In this paper we study the semileptonic decays of $B_c^- \to (η_c,J/ψ)l^-\barν_l$. We firstly evaluate the $B_c \to (η_c,J/Ψ)$ transition form factors $F_0(q^2)$, $F_+(q^2)$, $V(q^2)$ and $A_{0,1,2}(q^2)$ by employing the pQCD factorization approach, and then we calculate the branching ratios for all considered semileptonic decays. Based on the numerical results and the phenomenological analysis, we find that: (a) the pQCD predictions for the values of the $B_c \to η_c$ and $B_c \to J/Ψ$ transition form factors agree well with those obtained by using other methods; (b) the pQCD predictions for the branching ratios of the considered decays are $Br\left(B_c^- \toη_c e^-\barν_e(μ^-\barν_μ)\right) =(4.41^{+1.22}_{-1.09})\times10^{-3}$, $Br\left(B_c^- \toη_cτ^-\barν_τ\right) =(1.37^{+0.37}_{-0.34})\times10^{-3}$, $Br(B_c^- \to J/Ψe^-\barν_e(μ^-\barν_μ)) =(10.03^{+1.33}_{-1.18})\times10^{-3}$, and $Br\left(B_c^- \to J/Ψτ^-\barν_τ\right) =(2.92^{+0.40}_{-0.34})\times10^{-3}$; and (c) we also define and calculate two ratios of the branching ratios $R_{η_c}$ and $R_{J/Ψ}$, which will be tested by LHCb and the forthcoming Super-B experiments.

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arXiv2012

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

In this work, we study six tree-dominated $B \to a_1(1260) a_1(1260)$ and $b_1(1235) b_1(1235)$ decays in the perturbative QCD(pQCD) approach, where $a_1$($b_1$) is a $^3P_1$($^1P_1$) axial-vector meson. Based on the perturbative calculations and phenomenological analysis, we find that: (a) the CP-averaged branching ratio of $B^0 \to a_1^+ a_1^-$ decay in the pQCD approach is $54.7 \times 10^{-6}$, which agrees well with the current data and the predictions given in the QCD factorization approach within errors; (b) the numerical results for the decay rates of other five channels are found to be in the order of $10^{-6} \sim 10^{-5}$, which could be accessed at B factories and Large Hadron Collider(LHC) experiments; (c) other physical observables such as polarization fractions and direct CP-violating asymmetries are also investigated with the pQCD approach in the present work and the predictions can be confronted with the relevant experiments in the near future; (d) the different phenomenologies shown between $B \to a_1 a_1$ and $B \to b_1 b_1$ decays are expected to be tested by the ongoing LHC and forthcoming Super-B experiments, which could shed light on the typical QCD dynamics involved in these decay modes, as well as in $^3P_1$ meson $a_1$ and $^1P_1$ meson $b_1$.

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arXiv2012

The semileptonic decays $B/B_s \to (π, K)(l^+l^-,lν,ν\barν)$ in the perturbative QCD approach beyond the leading-order

In this paper we first calculate the form factors of $B \to (π,K)$ and $B_s \to K $ transitions by employing the perturbative QCD (pQCD) factorization approach with the inclusion of the next-to-leading-order(NLO) corrections, and then we calculate the branching ratios of the corresponding semileptonic decays $B/B_s \to (π, K)(l^+l^-,lν,ν\barν)$ (here $l$ denotes $e, μ$ and $τ$). Based on the numerical calculations and phenomenological analysis, we found the following results: (a) For $B \to (π, K)$ and $B_s \to K$ transition form factors $F_{0,+,\rmt}(q^2)$, the NLO pQCD predictions for the values of $F_{0,+,\rmt}(0)$ and their $q^2$-dependence agree well with those obtained from other methods; (b) For $\bar{B}^0 \to π^+l^-\barν_l, \bar{K}^0 l^+ l^- $ and $B^- \to π^0 l^-\barν_l, K^- l^+ l^-$ decay modes, the NLO pQCD predictions for their branching ratios agree very well with the measured values; (c) By comparing the pQCD predictions for $Br(\bar{B}^0 \to π^+l^-\barν_l)$ with the measured decay rate we extract out the magnitude of $V_{ub}$: $|V_{ub}|= (3.80^{+0.56}_{-0.50}(theor.)) \times 10^{-3}$; (d) We also defined several ratios of the branching ratios, $R_ν, R_C$ and $R_{N1,N2,N3}$, and presented the corresponding pQCD predictions, which will be tested by LHCb and the forthcoming Super-B experiments.

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arXiv2012

Implications on $η$-$η'$-glueball mixing from $B_{d/s} \to J/Ψη^{(')}$ Decays

We point out that the recent Belle measurements of the $B_{d/s} \to J/Ψη^{(')}$ decays imply large pseudoscalar glueball contents in the $η^{(\prime)}$ meson. These decays are studied in the perturbative QCD (PQCD) approach, considering the $η$-$η'$-$G$ mixing, where $G$ represents the pseudoscalar glueball. It is shown that the PQCD predictions for the $B_{d/s} \to J/Ψη^{(')}$ branching ratios agree well with the data for the mixing angle $ϕ_G\approx 30^\circ$ between the flavor-singlet state and the pure pseudoscalar glueball. Extending the formalism to the $η$-$η'$-$G$-$η_c$ tetramixing, the abnormally large observed $B_d\to Kη'$ branching ratios are also explained. The proposed mixing formalism is applicable to other heavy meson decays into $η^{(\prime)}$ mesons, and could be tested by future LHCb and Super-$B$ factory data.

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arXiv2012

Revisiting the pure annihilation decays $B_s\to π^+ π^-$ and $B^0 \to K^+ K^-$: the data and the pQCD predictions

In this work, we recalculate the charmless pure annihilation decays $B_s\to π^+ π^-$ and $B^0 \to K^+ K^-$ by using the perturbative QCD (pQCD) factorization approach, and compare the pQCD predictions with currently available experimental measurements. We used the same set of relevant input parameters and wave functions to make the calculations for the considered decay modes and found the following results: (a) one can provide a consistent pQCD interpretation for both the measured $Br(B_s^0 \to π^+ π^-)$ and $Br(B_d^0 \to K^+ K^-)$ simultaneously; (b) the pQCD predictions for $Br(B_s^0 \to π^+π^-)$ obtained by different authors are well consistent with each other; (c) our new pQCD prediction for $Br(B_d^0 \to K^+K^-)$ agree very well with the measured values from CDF and LHCb Collaboration; and (d) the CP-violating asymmetry ${\cal A}_{CP}(B_d^0 \to K^+K^-) \approx 16%$, which is large and may be detected at the LHCb experiment.

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arXiv2011

Study of the pure annihilation $B_c \to A_2 A_3$ decays

In this work, we calculate the {\it CP}-averaged branching ratios and the polarization fractions of the charmless hadronic $B_c \to A_2 A_3$ decays within the framework of perturbative QCD(pQCD) approach, where $A$ is either a light $^3P_1$ or $^1P_1$ axial-vector meson. These thirty two decay modes can occur through the annihilation topology only. Based on the perturbative calculations and phenomenological analysis, we find the following results: (a) the branching ratios of the considered thirty two $B_c\to A_2 A_3$ decays are in the range of $10^{-5}$ to $10^{-8}$; (b) $B_c\to a_1 b_1$, $\ov{K}_1^0 K_1^+$ and some other decays have sizable branching ratios and can be measured at the LHC experiments; (c) the branching ratios of $B_c \to A_2(^1P_1) A_3(^1P_1)$ decays are generally much larger than those of $B_c \to A_2(^3P_1) A_3(^3P_1)$ decays with a factor around (10 $\sim$ 100); (d) the branching ratios of $B_c \to \ov{K}_1^0 K_1^+$ decays are sensitive to the value of $θ_K$, which will be tested by the running LHC and forthcoming SuperB experiments; (e) the large longitudinal polarization contributions govern most considered decays and play the dominant role.

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arXiv2011

Charmless hadronic B_q to K_0^(1430) \bar{K}_0^(1430) decays in the pQCD approach

Based on the assumption of two-quark structure of the scalar $K_0^*(1430)$, the CP-averaged branching ratios(BRs) and CP-violating asymmetries of charmless hadronic $B_q(q=u,d,s,c) \to \kst \kstb$ decays are studied in the standard model(SM) by employing the perturbative QCD(pQCD) factorization approach. Our predictions are the following: (1) the CP-averaged BRs for $B_{q} \to \kst \kstb$ decays in both scenarios vary in the range of $10^{-6} \sim 10^{-4}$ in the SM; (2) the magnitudes of $\acp^{\rm dir}(B_u \to {\kst}^+ {\kstb}^0)$ and $\acp^{\rm dir}(B_{d,s} \to {\kst}^+ {\kst}^-)$ in Scenario 1 are much larger than those in Scenario 2 correspondingly; (3) there are no direct CP violations in $B_{d,s} \to {\kst}^0 {\kstb}^0$ and $B_c \to {\kst}^+ {\kstb}^0$ decays in the SM because of the pure penguin and tree topology, respectively. A measurement of our pQCD predictions at the predicted level will favor the $q\bar q$ structure of the scalar $\kst$ and help us to understand its physical properties and the involved QCD dynamics.

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arXiv2010

Light scalar mesons and charmless hadronic $B_c \to SP, SV$ decays in the perturbative QCD approach

In this work, based on the assumption of two-quark structure of the scalars, the charmless hadronic $B_c \to SP, SV$ decays(here, $S$, $P$, and $V$ denote the light scalar, pseudoscalar, and vector mesons, respectively) are investigated by employing the perturbative QCD(pQCD) factorization approach.From our numerical evaluations and phenomenological analysis, we find that (a) the pQCD predictions for the {\it CP}-averaged branching ratios(BRs) of the considered $B_c$ decays vary in the range of $10^{-5}$ to $10^{-8}$, which will be tested in the ongoing LHCb and forthcoming Super-B experiments, while the {\it CP}-violating asymmetries for these modes are absent naturally in the standard model because only one type tree operator is involved; %% (b) analogous to $B \to K^* η^{(\prime)}$ decays, $Br(B_c \to κ^+ η) \sim 5 \times Br(B_c \to κ^+ η^\prime)$ in the pQCD approach, which can be understood by the constructive and destructive interference between the $η_q$ and $η_s$ contributions to the $B_c \to κ^+ η$ and $B_c \to κ^+ η^\prime$ decays, however, $Br(B_c \to K_0^*(1430) η)$ is approximately equal to $Br(B_c \to K_0^*(1430) η')$ in both scenarios because the factorizable contributions from $η_s$ term play the dominant role in the considered two channels; %% (c) if $a_0(980)$ and $κ$ are the $q\bar q$ bound states, the pQCD predicted BRs for $B_c \to a_0(980) (π, ρ)$ and $B_c \to κK^{(*)}$ decays will be in the range of $10^{-6} \sim 10^{-5}$, which are within the reach of the LHCb experiments and could be measured in the near future; and %% (d) for the $a_0(1450)$ and $K_0^*(1430)$ channels, the BRs for $B_c \to a_0(1450) (π, ρ)$ and $B_c \to K_0^*(1430) K^{(*)}$ modes in the pQCD approach are found to be $(5 \sim 47) \times 10^{-6}$ and $(0.7 \sim 36) \times 10^{-6}$, respectively.

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arXiv2010

The double charm decays of B Mesons in the mSUGRA model

Based on the low energy effective Hamiltonian with naive factorization, we calculate the branching ratios(BRs) and CP asymmetries (CPAs) for the twenty three double charm decays $B/B_s \to D^{(*)}_{(s)} D^{(*)}_{(s)}$ in both the standard model (SM) and the minimal supergravity (mSUGRA) model. Within the considered parameter space, we find that (a) the theoretical predictions for the BRs, CPAs and the polarization fractions in the SM and the mSUGRA model are all consistent with the currently available data within $\pm 2σ$ errors; (b) For all the considered decays, the supersymmetric contributions in the mSUGRA model are very small, less than $7\%$ numerically. It may be difficult to observe so small SUSY contributions even at LHC.

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arXiv2010

Charmless hadronic $B_c \to VA, AA$ decays in the perturbative QCD approach

In this work, we calculate the branching ratios (BRs) and the polarization fractions of sixty two charmless two-body $B_c$ meson decays into final states involving one vector and one axial-vector meson ($VA$) or two axial-vector mesons($AA$) within the framework of perturbative QCD (pQCD) approach systematically, where $A$ is either a $^3P_1$ or $^1P_1$ axial-vector meson. All considered decay channels can only occur through the annihilation topologies in the standard model. Based on the perturbative calculations and phenomenological analysis, we find the following results: (i) the CP-averaged BRs of the considered sixty two $B_c$ decays are in the range of $10^{-5}$ to $10^{-9}$; (ii) since the behavior for $^1P_1$ meson is much different from that of $^3P_1$ meson, the BRs of $B_c \to A(^1P_1) (V, A(^1P_1))$ decays are generally larger than that of $B_c \to A(^3P_1) (V, A(^3P_1))$ decays in the pQCD approach; (iii) many considered decays modes, such as $B_c\to a_1(1260)^+ ω$, $b_1(1235) ρ$, etc, have sizable BRs within the reach of the LHCb experiments; (iv) the longitudinal polarization fractions of most considered decays are large and play the dominant role; (v) the pQCD predictions for several decays involving mixtures of $^3P_1$ and/or $^1P_1$ mesons are highly sensitive to the values of the mixing angles, which will be tested by the ongoing LHC and forthcoming Super-B experiments; (vi) the CP-violating asymmetries of these considered $B_c$ decays are absent in the standard model because only one type tree operator is involved.

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arXiv2010

B \to K_0^*(1430) η^{(\prime)} decays in the pQCD approach

Based on the assumption of two-quark structure of the scalar meson $K_0^*(1430)$, we calculate the CP-averaged branching ratios for $B \to K_0^*(1430) \etap$ decays in the framework of the perturbative QCD (pQCD) approach here. We perform the evaluations in two scenarios for the scalar meson spectrum. We find that: (a) the pQCD predictions for $Br(B \to K_0^*(1430) η^{(\prime)})$ is $10^{-5} - 10^{-6}$, basically agree with the data within large theoretical uncertainty; (b) the agreement between the pQCD predictions and the data in the scenario I is better than that in the scenario II, which can be tested by the forthcoming LHC experiments; (c) the annihilation contributions play an important role for these considered decays.

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arXiv2010

Branching ratios of $B_c \to A P $ decays in the perturbative QCD approach

In this paper we calculate the branching ratios (BRs) of the 32 charmless hadronic $B_c \to A P$ decays ($A=a_1(1260),b_1(1235),K_1(1270),K_1(1400), f_1(1285),f_1(1420),h_1(1170),h_1(1380)$) by employing the perturbative QCD(pQCD) factorization approach. These considered decay channels can only occur via annihilation type diagrams in the standard model. From the numerical calculations and phenomenological analysis, we found the following results: (a) the pQCD predictions for the BRs of the considered $B_c$ decays are in the range of $10^{-6}$ to $10^{-8}$, while the CP-violating asymmetries are absent because only one type tree operator is involved here; (b) the BRs of $ΔS= 0$ processes are generally much larger than those of $ΔS =1$ ones due to the large CKM factor of $|V_{ud}/V_{us}|^2\sim 19$; (c) since the behavior for $^1P_1$ meson is much different from that of $^3P_1$ meson, the BRs of $B_c \to A(^1P_1) P$ decays are generally larger than that of $B_c \to A(^3P_1) P$ decays; (d) the pQCD predictions for the BRs of $B_c \to (K_1(1270), K_1(1400)) \etap $ and $(K_1(1270), K_1(1400)) K$ decays are rather sensitive to the value of the mixing angle $θ_K$.

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arXiv2009

Study of scalar meson $a_0(980)$ from $B \to a_0(980)π$ Decays

In this paper, we calculate the branching ratios and the direct CP-violating asymmetries for decays $\bar{B}^0\to a^0_0(980)π^0, a^+_0(980)π^-, a^-_0(980)π^+$ and $B^-\to a^0_0(980)π^-, a^-_0(980)π^0$ by employing the perturbative QCD factorization approach. Although the light scalar meson $a_0(980)$ is widely perceived as primarily the four-quark bound states, the calculation shows that the 2-quark model supposition for $a_0(980)$ can not be ruled out by the currently available experiment upper limits. In these considered decays, the branching ratio for the $B^-\to a^0_0(980)π^-$ is the largest, $2.8\times 10^{-6}$, while its direct CP asymmetry is the smallest, $\sim 14%$. Although the direct CP asymmetries for the decays $\bar{B}^0\to a^0_0(980)π^0, B^-\to a^-_0(980)π^0$ are large, about $(70\thicksim80)%$, it is still difficult to measure them, since their branching ratios are small, around $(4\thicksim5)\times 10^{-7}$.

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arXiv2009

$B \to (\jpsi,η_c) K$ decays in the perturbative QCD approach

In this paper, we calculated the $B \to (\jpsi, η_c) K$ decays in the perturbative QCD approach with the inclusion of the partial next-to-leading order (NLO) contributions. We found that (a) when the large enhancements from the known NLO contributions are taken into account, the NLO pQCD predictions for the branching ratios are the following: $Br(B^0 \to \jpsi K^0) = 5.2^{+3.5}_{-2.8}\times 10^{-4}$, $Br(B^+ \to \jpsi K^+) = 5.6^{+3.7}_{-2.9}\times 10^{-4}$, $Br(B^0 \to η_c K^0) = 5.5^{+2.3}_{-2.0}\times 10^{-4}$, $Br(B^+ \to η_c K^+) = 5.9^{+2.5}_{-2.1}\times 10^{-4}$, which are roughly 40% smaller than the measured values, but basically agree with the data within $2-σ$ errors; (b) the NLO pQCD predictions for the CP-violating asymmetries of $B \to (\jpsi,η_c)K$ decays agree perfectly with the data.

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