arXiv subjects

Zuo-Hong Li

Publications and source records attributed to Zuo-Hong Li.

At least 19 recordsLinked to original sources

arXiv2015

Impact of Family Non-universal $Z^\prime$ Boson on Pure Annihilation $B_s \to π^+ π^-$ and $B_d \to K^+ K^-$ Decays

We study the $B_s \to π^+ π^-$ and $B_d \to K^+ K^-$ decays in the standard model and the family non-universal $Z^\prime$ model. Since none of the quarks in final states is the same as the initial quark, these decay modes can occur only via power-suppressed annihilation diagrams. Despite the consistence of the standard model prediction with the available data, there is a surviving room for a light $Z^\prime$ boson. Taking into account the $Z^\prime$ contribution, we find theoretical results for branching fractions can better accommodate the data. With the relevant data, we also derive a constraint on the parameter space for the $Z^\prime$. Moreover, for the $B_d \to K^+ K^-$, both the direct and the mixing-induced $CP$ asymmetry are sensitive to the couplings between $Z^\prime$ and fermions in the parameter spaces constrained by data. The measurements at future experimental facilities, including the LHC-b, Belle-II and the proposed high energy $e^+e^-$ collider, will provide us useful hints for direct searching for the light $Z^\prime$ boson.

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arXiv2015

Study of $B \to K_0^(1430)K^{()}$ decays in QCD Factorization Approach

Within the QCD factorization approach, we calculate the branching fractions and $CP$ asymmetry parameters of 12 $B \to K_0^*(1430)K^{(*)}$ decay modes under the assumption that the scalar meson $K_0^*(1430)$ is the first excited state or the lowest lying ground state in the quark model. We find that the decay modes with the scalar meson emitted, have large branching fractions due to the enhancement of large chiral factor $r_χ^{K_0^*}$. The branching fractions of decays with the vector meson emitted, become much smaller owing to the smaller factor $r_χ^{K^*}$. Moreover, the annihilation type diagram will induce large uncertainties because of the extra free parameter dealing with the endpoint singularity. For the pure annihilation type decays, our predictions are smaller than that from PQCD approach by 2-3 orders of magnitudes. These results will be tested by the ongoing LHCb experiment, forthcoming Belle-II experiment and the proposing circular electron-positron collider.

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arXiv2014

$B\to π\ell^{+}\ell^{-}$ decays revisited in the standard model

A new estimate is presented of the dileptonic $B$ decays $B\toπ\ell^+\ell^-(\ell=e,μ,τ)$ in naive factorization within the standard-model (SM) framework. Using a combination of several approaches, we investigate the behavior of the $B\to π$ form factors in the entire region of the momentum transfer squared $q^2$. For the vector and scalar form factors, we employ the light cone sum rule (LCSR) with a chiral current correlator to estimate, at twist-2 next-to-leading order (NLO) accuracy, their shapes in small and intermediate kinematical region. Then a simultaneous fit to a Bourrely-Caprini-Lellouch (BCL) parametrization is performed of the sum rule predictions and the corresponding lattice QCD (LQCD) results available at some high $q^2$'s. The same approach is applied for the tensor form factor, except that at large $q^2$ we use as input the LQCD data on the corresponding $B\to K$ form factor in combination with a $SU_F(3)$ symmetry breaking ansatz. Employing the fitted BCL parameterizations, we evaluate, as an illustrative example, several of the observables of the charged decay modes $B^-\toπ^-\ell^+\ell^-$, including the dilepton invariant mass distribution and branching ratio. For the dielectron and dimuon modes, the branching ratios are estimated at $\mathcal{B}(B^-\toπ^-e^+e^-)=(2.263^{+0.227}_{-0.192})\times10^{-8}$ and $\mathcal{B}(B^-\toπ^-μ^+μ^-)=(2.259^{+0.226}_{-0.191}) \times10^{-8}$. The latter shows an excellent agreement with the recent experimental measurement at LHCb and hence puts a stringent constraint on the contribution from possible new physics. We arrive at, for the ditau mode, $\mathcal{B}(B^-\toπ^-τ^+τ^-)=(1.017^{+0.118}_{-0.139})\times10^{-8}$, which is one order of magnitude larger than the existing theoretical predictions.

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arXiv2014

Study Majorana Neutrino Contribution to B-meson Semi-leptonic Rare Decays

B meson semi-leptonic rare decays are sensitive to new physics beyond standard model. We study the $B^{-}\to π^{-}μ^{+}μ^{-}$ process and investigate the Majorana neutrino contribution to its decay width. The constraints on the Majorana neutrino mass and mixing parameter are obtained from this decay channel with the latest LHCb data. Utilizing the best fit for the parameters, we study the lepton number violating decay $B^{-}\to π^{+}μ^{-}μ^{-}$, and find its branching ratio is about $6.4\times10^{-10}$, which is consistent with the LHCb data reported recently.

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arXiv2012

Form factors $f^{B\to π}_+(0)$ and $f^{D\to π}_+(0)$ in $QCD$ and determination of $|V_{ub}|$ and $|V_{cd}|$

We present a QCD study on $B, D\toπ$ semileptonic transitions at zero momentum transfer and an estimate of magnitudes of the associated CKM matrix elements. Light cone sum rules (LCSRs) with chiral correlator are applied to calculate the form factors $f^{B\to π}_+(0)$ and $f^{D\to π}_+(0)$. We show that there is no twist-3 and-5 component involved in the light-cone expansions such that the resulting sum rules have a good convergence and offer an understanding of these form factors at twist-5 level. A detailed $\mathcal{O}(α_s)$ computation is carried out in leading twist-2 approximation and the $\bar{MS}$ masses are employed for the underlying heavy quarks. With the updated inputs and experimental data, we have $f^{B\to π}_+(0)=0.28^{+0.05}_{-0.02}$ and $|V_{ub}|=(3.4^{+0.2}_{-0.6}\pm0.1\pm0.1)\times10^{-3}$; $f^{D\to π}_+(0)=0.62\pm0.03$ and $|V_{cd}|=0.244\pm0.005\pm0.003\pm0.008$. As a by-product, a numerical estimate for the decay constant $f_D$ is yielded as $f_{D}=190^{+12}_{-11}\mathrm{MeV}$.

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arXiv2011

$B_{(s)}\to S$ transitions in the light cone sum rules with the chiral current

$B_{(s)}$ semi-leptonic decays to the light scalar meson, $B_{(s)}\to S l\barν_l, S l \bar{l}\,\,(l=e,μ,τ)$, are investigated in the QCD light-cone sum rules (LCSR) with chiral current correlator. Having little knowledge of ingredients of the scalar mesons, we confine ourself to the two quark picture for them and work with the two possible Scenarios. The resulting sum rules for the form factors receive no contributions from the twist-3 distribution amplitudes (DA's), in comparison with the calculation of the conventional LCSR approach where the twist-3 parts play usually an important role. We specify the range of the squared momentum transfer $q^2$, in which the operator product expansion (OPE) for the correlators remains valid approximately. It is found that the form factors satisfy a relation consistent with the prediction of soft collinear effective theory (SCET). In the effective range we investigate behaviors of the form factors and differential decay widthes and compare our calculations with the observations from other approaches. The present findings can be beneficial to experimentally identify physical properties of the scalar mesons.

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arXiv2009

Unparticle-Induced Lepton Flavor Violating Decays τ^- ->l^- (V^0, ~P^0)

We make an evaluation of the lepton flavor violating (LFV) decays $τ\to \ell (V^0, P^0)$, where $\ell=e$ or $μ$ and $V^0(P^0)$ is a neutral vector (pseudo-scalar) meson, in the context of unparticle physics. The constraints are investigated systematically on the related coupling parameters from all the available experimental data, and the parameter values are specified appropriately. The results show that whereas over the whole parameter space allowed by experiments all the $τ\to \ell P^0$ modes have a branching ratio too small to be measurable experimentally, in a large subspace as observed all of the $τ\to \ell V^0$ modes get simultaneously a branching ratio as high as ${\cal O}(10^{-10}-10^{-8})$, which is reachable at the LHC and super B factory. The important implications are drawn.

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arXiv2008

Heavy-to-light transition form factors and their relations in light-cone QCD sum rules

The improved light-cone QCD sum rules by using chiral current correlator is systematically reviewed and applied to the calculation of all the heavy-to-light form factors, including all the semileptonic and penguin ones. By choosing suitable chiral currents, the light-cone sum rules for all the form factors are greatly simplified and depend mainly on one leading twist distribution amplitude of the light meson. As a result, relations between these form factors arise naturally. At the considered accuracy these relations reproduce the results obtained in the literature. Moreover, since the explicit dependence on the leading twist distribution amplitudes is preserved, these relations may be more useful to simulate the experimental data and extract the information on the distribution amplitude.

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arXiv2008

Semileptonic $B(B_s, B_c)$ decays in the light-cone QCD sum rules

Semileptonic $B$($B_s, B_c$) decays are investigated systematically in the light-cone QCD sum rules. Special emphasis is put on the LCSR calculation on weak form factors with an adequate chiral current correlator, which turns out to be particularly effective to control the pollution by higher twist components of spectator mesons. The result for each channel depends on the distribution amplitude of the the producing meson. The leading twist distribution amplitudes of the related heavy mesons and charmonium are worked out by a model approach in the reasonable way. A practical scenario is suggested to understand the behavior of weak form factors in the whole kinematically accessible ranges. The decay widths and branching ratios are estimated for several $B$($B_c$) decay modes of current interest.

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arXiv2007

Systematic Study on QCD Interactions of Heavy Mesons with $ρ$ Meson

The strong interactions of the negative-parity heavy mesons with $ρ$ meson may be described consistently in the context of an effective lagrangian, which is invariant under isospin SU(2) transformation. Four coupling constants $g_{HHρ}$, $f_{H^*Hρ}$, $g_{H^*H^*ρ}$ and $f_{H^*H^*ρ}$ enter the effective lagrangian, where $H$ $(H^*)$ denotes a pseudoscalar bottom or charm meson (the corresponding vector meson). Using QCD light cone sum rule (LCSR) method and, as inputs, the hadronic parameters updated recently, we give an estimate of $g_{H^*H^*ρ}$ and $f_{H^*H^*ρ}$, about which little was known before, and present an improved result for $g_{HHρ}$ and $f_{H^*Hρ}$. Also, we examine the heavy quark asymptotic behavior of these nonperturbative quantities and assess the two low energy parameters $β$ and $λ$ of the corresponding effective chiral lagrangian.

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arXiv2006

Form Factor for $B{\to}D l\tildeν$ in Light-Cone Sum Rules With Chiral Current Correlator

Within the framework of QCD light-cone sum rules (LCSR), we calculate the form factor for $B{\to}D l\tildeν$ transitions with chiral current correlator. The resulting form factor depends on the distribution amplitude(DA) of the $D$-meson. We try to use three kinds of DA models of the $D$-meson. In the velocity transfer region $1.14 < y < 1.59$, which renders the Operator Product Expansion (OPE) near light-cone $x^2=0$ go effectively, the yielding behavior of form factor is in agreement with that extracted from the data on $ B\to D l\tildeν$, within the error. In the larger recoil region $1.35 < y < 1.59$, the results are observed consistent with those of perturbative QCD (pQCD). The presented calculation can play a bridge role connecting those from the lattice QCD with the heavy quark symmetry and perturbative QCD(pQCD) to have an all-around understanding of $B{\to}D l\tildeν$ transitions.

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arXiv2006

Importance of Higher Twist Effects to Understand Charmed Color-Suppressed $B$ Decays

Working within the framework of the QCD light cone sum rules (LCSR), we compute and discuss the nonfactorizable higher twist effect in $\bar{B}^0\to D^{*0}π^0$ to make an all-around examination of its role in the charmed color-suppressed B decays. Analogously to the case of $\bar{B}^0\to D^{0}π^0$, such effect turns out to be of the same strong phase as the factorizable amplitude, and modifies constructively the magnitude by order $(40-90)%$ so that the effective coefficient $a_2^{f}=C_1+C_2/3$ receives a positive correction comparable numerically with it. Nonleading as the soft effect in question is, our findings for it, along with the previous LCSR analyses of $\bar{B}^0\to D^{0}π^0$, are suggestive of the dominance of soft exchanges in these charmed color suppressed B decays. Also, the emphases are put on importance of understanding intensively various related higher twist and transverse momentum effects to interpret the data on $B \to D^{0(*0)}(π^0,η,η'),J/ψK^{(*)}$.

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arXiv2004

$B\to Kπ$ Decays with $1/m_b$ Corrections in $QCD$ Factorization

It is commonly believed that a careful investigation of the subleading terms is crucial for a better understanding of the $QCD$ factorization in charmless B decays. In this work the penguin-dominated $B\to Kπ$ decays are discussed systematically, including the subleading corrections in $1/m_b$ due to soft and hard gluons, besides the annihilation contributions. Soft-gluon effects for all the relevant 4-quark effective operators are calculated within the framework of the light-cone QCD sum rules (LCSR). Our observation is that such soft and hard corrections are less important than the annihilation effects, enhancing only the branching ratios by a few percent; the resultant increase in the branching ratios due to the overall ${\cal O}(1/m_b)$ effects is between about $(22-27)%$ of the QCD factorization results with the ${\cal O}(α_s)$ corrections, as the weak phase $γ(=\textmd{Im}V_{ub}^*)$ ranges from $40^0$ to $80^0$. Impacts of the involved uncertainties are discussed in some details.

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arXiv2004

Soft Nonfactorizable Contribution to \bar{B}^0 \to D^0π^0

For the color-suppressed $\bar{B}^0\longrightarrow D^{0}π^{0}$ decay, nonfactorizable contributions are expected to be leading and naive factorization description breaks down. We estimate $1/m_b$ power-suppressed nonfactorizable effect in $\bar{B}^0\longrightarrow D^{0}π^{0}$, which is due to soft exchange between the emitted heavy-light quark pair and $Bπ$ system, in the framework of QCD light-cone sum rules (LCSR). The resulting correction to the decay amplitude is found to be numerically comparable with the corresponding factorizable piece, estimated at about $(50-110)%$ of the latter. The relevant parameter $a_2$ receives a positive number contribution, due to the factorizable correction and the power-suppressed soft effect. Our findings would be crucial to phenomenological understanding of the $\bar{B}^0\longrightarrow D^{0}π^{0}$ decay.

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arXiv2002

Strong Couplings of Heavy Mesons to A Light Vector Meson in QCD

We make a detailed analysis of the $BBρ(DDρ)$ and $B^*Bρ(D^{*}Dρ)$ strong couplings $g_{BBρ}(g_{DDρ})$ and $g_{B^*Bρ}(g_{D^{*}Dρ})$ using QCD light cone sum rules(LCSR). The existing some negligence is pointed out in the previous LCSR calculation on $g_{B^*Bρ} (g_{D^{\ast}Dρ}$) and an updated estimate is presented. Our findings can be used to understand the behavior of the $B,D \to ρ$ semileptonic form factors at large momentum transitions.

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arXiv2002

Reexamined radiative Decay $ B_{q}^*\to B_{q}γ$ in Light Cone QCD

The radiative decay $ B_{q}^*\to B_{q}γ(q=u,d, or s) $ is reexamined with a modified light-cone QCD sum rule method, in which adequate chiral operators are chosen as the interpolating fields in the correlators used for a sum rule estimate of the relevant coupling $ g_{B_{q}^*B_{q}γ} $. The resulting sum rules not only show the physical picture consistent with the underlying physics in $ B_{q}^*\to B_{q}γ$ but also avoid the pollution by the nonlocal matrix element $< γ(q) | \bar{q}(x) γ_μγ_{5}q(0) | 0>$, which starts with twist-3 and thus may bring a large uncertainty to the sum rule predictions. Also, a comparison is made with the previous results from light-cone QCD sum rules and chiral perturbation theory.

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arXiv2001

The heavy-to-light transitions in the light-cone QCD sum rules

We have analyzed the $B\to π$ and $B_{s}\to K$ semileptonic form factors and $B\to Vγ(V=K^*,ρ,ω)$ processes in the light-cone QCD sum rules. In order to enhance the predictivity and reliability of numerical results the chiral-current correlator is employed and the twist-3 light-cone wavefunction can be effectively eliminated from the sum rules.

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arXiv2001

The $B_{s}\to K$ Form Factor in The Whole Kinematically Accessible Range

A systematic analysis is presented of the $B_{s}\to K$ form factor $f(q^{2}) $ in the whole range of momentum transfer $q^{2}$, which would be useful to analyzing the future data on $B_{s}\to K$ decays and extracting $| V_{ub}|$. With a modified QCD light cone sum rule (LCSR) approach, in which the contributions cancel out from the twist 3 wavefunctions of $K$ meson, we investigate in detail the behavior of $f(q^{2})$ at small and intermediate $q^{2}$ and the nonperturbative quantity $f_{B^{\ast}}g_{B^{\ast}B_{s}K}$ $(f_{B^{\ast}}$ is the decay constant of $B^{\ast}$ meson and $g_{B^{\ast}B_{s}K}$ the $B^{\ast}B_{s}K$ strong coupling), whose numerical result is used to study $q^{2}$ dependence of $f(q^{2})$ at large $q^{2}$ in the single pole approximation. Based on these findings, a form factor model from the best fit is formulated, which applies to the calculation on $f(q^{2})$ in the whole kinematically accessible range. Also, a comparison is made with the standard LCSR predictions.

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