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Tao Huang

Publications and source records attributed to Tao Huang.

At least 325 records · Page 18Linked to original sources
arXiv2008

Kaon Electromagnetic Form Factor within the $k_T$ Factorization Formalism and It's Light-Cone Wave Function

We present a systematical study on the kaon electromagnetic form factors $F_{K^{\pm},K^0,\bar{K}^0}(Q^2)$ within the $k_T$ factorization formalism, where the transverse momentum effects, the contributions from the different helicity components and different twist structures of the kaon light-cone (LC) wave function are carefully analyzed for giving a well understanding of the hard contributions at the energy region where pQCD is applicable. The right power behavior of the hard contribution from the higher helicity components and from the higher twist structures can be obtained by keeping the $k_T$ dependence in the hard amplitude. Our results show that the $k_T$ dependence in LC wave function affects the hard and soft contributions substantially and the power-suppressed terms (twist-3 and higher helicity components) make an important contribution below $Q^2\sim several GeV^2$ although they drop fast as $Q^2$ increasing. The parameters of the proposed model wave function can be fixed by the first two moments of its distribution amplitude and other conditions. By varying the first two moments $a^K_1(1GeV)$ and $a^K_2(1GeV)$ with the region of $0.05\pm0.02$ and $0.10\pm 0.05$ respectively, we find that the uncertainty of the kaon electromagnetic form factor is rather small.

hep-ph↗
arXiv2008

SU_f(3)-Symmetry Breaking Effects of the B\to K Transition Form Factor in the QCD Light-Cone Sum Rules

We present an improved calculation of the $B\to K$ transition form factor with chiral current in the QCD light-cone sum rule (LCSR) approach. Under the present approach, the most uncertain twist-3 contribution is eliminated. And the contributions from the twist-2 and the twist-4 structures of the kaon wave function are discussed, including the $SU_f(3)$-breaking effects. One-loop radiative corrections to the kaonic twist-2 contribution together with the leading-order twist-4 corrections are studied. The $SU_f(3)$ breaking effect is obtained, $ \frac{F^{B\to K}_{+}(0)}{F^{B\toπ}_{+}(0)}=1.16\pm 0.03$. By combining the LCSR results with the newly obtained perturbative QCD results that have been calculated up to ${\cal O}(1/m^2_b)$ in Ref.\cite{hwf0}, we present a consistent analysis of the $B\to K$ transition form factor in the large and intermediate energy regions.

hep-ph↗
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.

hep-ph↗
arXiv2007

$B\to K$ Transition Form Factor up to ${\cal O}(1/m^2_b)$ within the $k_T$ Factorization Approach

In the paper, we apply the $k_T$ factorization approach to deal with the $B\to K$ transition form factor $F^{B\to K}_{+,0}(q^2)$ in the large recoil regions. The B-meson wave functions $Ψ_B$ and $\barΨ_B$ that include the three-particle Fock states' contributions are adopted to give a consistent PQCD analysis of the form factor up to ${\cal O} (1/m^2_b)$. It has been found that both the wave functions $Ψ_B$ and $\barΨ_B$ can give sizable contributions to the form factor and should be kept for a better understanding of the $B$ meson decays. Then the contributions from different twist structures of the kaon wavefunction are discussed, including the $SU_f(3)$-breaking effects. A sizable contribution from the twist-3 wave function $Ψ_p$ is found, whose model dependence is discussed by taking two group of parameters that are determined by different distribution amplitude moments obtained in the literature. It is also shown that $F^{B\to K}_{+,0}(0)=0.30\pm0.04$ and $[F^{B\to K}_{+,0}(0)/F^{B\to π}_{+,0}(0)]=1.13\pm0.02$, which are more reasonable and consistent with the light-cone sum rule results in the large recoil regions.

hep-ph↗
arXiv2007

Couplings of the Rho Meson in a Holographic dual of QCD with Regge Trajectories

The couplings $g_{ρHH}$ of the $ρ$ meson with any hadron H are calculated in a holographic dual of QCD where the Regge trajectories for mesons are manifest. The resulting couplings grow linearly with the exciting number of H, thus are far from universal. A simple argument has been given for this behavior based on quasi-classical picture of excited hadrons. It seems that in holographic duals with exact Regge trajectories the $g_{ρHH}$ universality should be violated. The $ρ$-dominance for the electromagnetic form factors of H are also strongly violated, except for the lowest state, the pion. Quite unexpected, the form factor of the pion is completely saturated by the contribution of the $ρ$. The asymptotic behavior of the form factors are also calculated, and are found to be perfectly accordant with the prediction of conformal symmetry and pertubative QCD.

hep-ph↗
arXiv2007

Fast recognition of single molecules based on single event photon statistics

Mandel Q-parameter, which is determined from single event photon statistics, provides an alternative to differentiate single-molecule with fluorescence detection. In this work, by using the Q-parameter of the sample fluorescence compared to that of an ideal double-molecule system with the same average photon number, we present a novel and fast approach for identifying single molecules based on single event photon statistics analyses, compared with commonly used two-time correlation measurements. The error estimates for critical values of photon statistics are also presented for single-molecule determination.

quant-ph↗
arXiv2007

Diquark and light four-quark states

Four-quark states with different internal clusters are discussed within the constituent quark model. It is pointed out that the diquark concept is not meaningful in the construction of a tetraquark interpolating current in the QCD sum rule approach, and hence existing sum-rule studies of four-quark states are incomplete. An updated QCD sum-rule determination of the properties of diquark clusters is then used as input for the constituent quark model to obtain the masses of light $0^{++}$ tetraquark states ({\it i.e.\} a bound state of two diquark clusters). The results support the identification of $σ(600)$, $f_0(980)$ and $a_0(980)$ as the $0^{++}$ light tetraquark states, and seem to be inconsistent with the tetraquark state interpretation of the new BES observations of the near-threshold $p\bar p$ enhancements, X(1835) and X(1812), with the possible exception that X(1576) may be an "exotic" first orbital excitation of $f_0(980)$ or $a_0(980)$.

hep-ph↗
arXiv2007

Semileptonic $B_c$ decays and Charmonium distribution amplitude

In this paper we study the semileptonic decays of the $B_c$ meson in the Light-Cone Sum Rule (LCSR) approach. The result for each channel depends on the corresponding distribution amplitude of the final meson. For the case of $B_c$ decaying into a pseudoscalar meson, to twist-3 accuracy only the leading twist distribution amplitude (DA) is involved if we start from a chiral current. If we choose a suitable chiral current in the vector meson case, the main twist-3 contributions are also eliminated and we can consider the leading twist contribution only. The leading twist distribution amplitudes of the charmonium and other heavy mesons are given by a model approach in the reasonable way. Employing this charmonium distribution amplitude we find the cross section $σ(e^+e^-\to J/ψ+η_c)\simeq22.8 {fb}$ which is consistent with Belle and BaBar's data. Based on this model, we calculate the form factors for various $B_c$ decay modes in the corresponding regions. Extrapolating the form factors to the whole kinetic regions, we get the decay widths and branching ratios for various $B_c$ decay modes including their $τ$ modes when they are kinematically accessible.

hep-ph↗
arXiv2007

Light Four-quark States and New Observations by BES

Four-quark states are discussed within the constituent quark model. Incompleteness of existed studies of four-quark state with QCD sum rule is analyzed. The masses of diquark cluster were determined by QCD sum rules, and light four-quark states masses were obtained in terms of the diquark. The four-quark state possibility of the newly observed near-threshold p\bar p enhancement, X(1835), X(1812) and X(1576) by BES is discussed.

hep-ph↗
arXiv2007

Determination of the $η$ and $η'$ Mixing Angle from the Pseudoscalar Transition Form Factors

The possible range of $η-η'$ mixing angle is determined from the transition form factors $F_{ηγ}(Q^2)$ and $F_{η' γ}(Q^2)$ with the help of the present experimental data. For such purpose, the quark-flavor mixing scheme is adopted and the pseudoscalar transition form factors are calculated under the light-cone pQCD framework, where the transverse momentum corrections and the contributions beyond the leading Fock state have been carefully taken into consideration. We construct a phenomenological expression to estimate the contributions to the form factors beyond the leading Fock state based on their asymptotic behavior at $Q^2\to 0$ and $Q^2\to\infty$. By taking the quark-flavor mixing scheme, our results lead to $ϕ= 38.0^{\circ}\pm 1.0^{\circ}\pm 2.0^{\circ}$, where the first error coming from experimental uncertainty and the second error coming from the uncertainties of the wavefunction parameters. The possible intrinsic charm component in $η$ and $η'$ is discussed and our present analysis also disfavors a large portion of intrinsic charm component in $η$ and $η'$, e.g. $|f^c_{η'}|\le 50 {\rm MeV}$.

hep-ph↗
arXiv2006

$B_c(B){\to}D l\tildeν$ form factors in Light-Cone Sum Rules and the $D$-meson distribution amplitude

In this paper we calculate the weak form factors of the decays $B_c(B)\to Dl\tildeν$ by using the chiral current correlator within the framework of the QCD light-cone sum rules (LCSR). The expressions of the form factors only depend on the leading twist distribution amplitude (DA) of the $D$ meson. Three models of the $D$-meson distribution amplitude are employed and the calculated form factor $F_{B_c\to D}(0)$ is given. Our prediction, by using the $D$-meson distribution amplitude with the exponential suppression at the end points, is compatible with other approaches, and favors the three-points sum rules (3PSR) approach with the Coulumb corrections included.

hep-ph↗
arXiv2006

A Comprehensive Analysis on the Pion-Photon Transition Form Factor Beyond the Leading Fock State

We perform a comprehensive analysis of the pion-photon transition form factor $F_{πγ}(Q^2)$ involving the transverse momentum corrections with the present CLEO experimental data, in which the contributions beyond the leading Fock state have been taken into consideration. As is well-known, the leading Fock-state contribution dominates of $F_{πγ}(Q^2)$ at large momentum transfer ($Q^2$) region. One should include the contributions beyond the leading Fock state in small $Q^2$ region. In this paper, we construct a phenomenological expression to estimate the contributions beyond the leading Fock state based on its asymptotic behavior at $Q^2\to0$. Our present theoretical results agree well with the experimental data in the whole $Q^2$ region. Then, we extract some useful information of the pionic leading twist-2 distribution amplitude (DA) by comparing our results of $F_{πγ}(Q^2)$ with the CLEO data. By taking best fit, we have the DA moments, $a_2(μ_0^2)=0.002^{+0.063}_{-0.054}$, $a_4(μ_0^2)=-0.022_{-0.012}^{+0.026}$ and all of higher moments, which are closed to the asymptotic-like behavior of the pion wavefunction.

hep-ph↗
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.

hep-ph↗
arXiv2006

B-Meson Wavefunction with Contributions from 3-particle Fock States

The B-meson light-cone wavefunctions, $Ψ_{\pm}(ω,z^2)$, are investigated up to the next-to-leading order in Fock state expansion in the heavy quark limit. In order to know the transverse momentum dependence of the B-meson wavefunctions with 3-particle Fock states' contributions, we make use of the relations between 2- and 3- particle wavefunctions derived from the QCD equations of motion and the heavy quark symmetry, especially two constraints derived from the gauge field equation of motion are employed. Our results show that the use of gluon equation of motion can give a constraint on the transverse momentum dependence $χ(ω,\mathbf{k}_\perp)$ of the B-meson wavefunctions, whose distribution tends to be a hyperbola-like curve under the condition $0<c_1<1$, which is quite different from the WW type wavefunctions, whose transverse momentum dependence $χ^{WW}(ω,\mathbf{k}_\perp)$ is merely a delta function. Based on the derived results, we propose a simple model for the B-meson wavefunctions with 3-particle Fock states' contributions.

hep-ph↗
arXiv2005

Pion Electromagnetic Form Factor in the $K_T$ Factorization Formulae

Based on the light-cone (LC) framework and the $k_T$ factorization formalism, the transverse momentum effects and the different helicity components' contributions to the pion form factor $F_π(Q^2)$ are recalculated. In particular, the contribution to the pion form factor from the higher helicity components ($λ_1+λ_2=\pm 1$), which come from the spin-space Wigner rotation, are analyzed in the soft and hard energy regions respectively. Our results show that the right power behavior of the hard contribution from the higher helicity components can only be obtained by fully keeping the $k_T$ dependence in the hard amplitude, and that the $k_T$ dependence in LC wavefunction affects the hard and soft contributions substantially. A model for the twist-3 wavefunction $ψ_p(x,\mathbf{k_\perp})$ of the pion has been constructed based on the moment calculation by applying the QCD sum rules, whose distribution amplitude has a better end-point behavior than that of the asymptotic one. With this model wavefunction, the twist-3 contributions including both the usual helicity components ($λ_1+λ_2=0$) and the higher helicity components ($λ_1+λ_2=\pm 1$) to the pion form factor have been studied within the modified pQCD approach. Our results show that the twist-3 contribution drops fast and it becomes less than the twist-2 contribution at $Q^2\sim 10GeV^2$. The higher helicity components in the twist-3 wavefunction will give an extra suppression to the pion form factor. When all the power contributions, which include higher order in $α_s$, higher helicities, higher twists in DA and etc., have been taken into account, it is expected that the hard contributions will fit the present experimental data well at the energy region where pQCD is applicable.

hep-ph↗
arXiv2005

Twist-3 distribution amplitudes of the pion and kaon from the QCD sum rules

Twist-3 distribution amplitudes of the pion and kaon are studied in this paper. We calculate the fist several moments for the twist-3 distribution amplitudes (ϕ_{p,σ}^πand ϕ_{p,σ}^K) of the pion and kaon by applying the QCD sum rules. Our results show that, (i) the first three moments of ϕ_p^K and the first two moments of ϕ_p^πand ϕ_σ^{π,K} of the pion and kaon can be obtained with 30% uncertainty; (ii) the fourth moment of the ϕ_p^πand the second moment of the ϕ_σ^K can be obtained when the uncertainty are relaxed to 35%; (iii) the fourth moment of the ϕ_σ^πcan be obtained only when the uncertainty are relaxed to 40%; (iv) we have m_{0π}^p=1.10\pm 0.08 {\rm GeV} and m_{0K}^p=1.25\pm 0.15 {\rm GeV} after including the α_s-corrections to the perturbative part. These moments will be helpful for constructing the twist-3 wave functions of the pion and kaon.

hep-ph↗
arXiv2005

Consistent Analysis of the $B\toπ$ Transition Form Factor in the Whole Physical Region

In the paper, we show that the $B\toπ$ transition form factor can be calculated by using the different approach in the different $q^2$ regions and they are consistent with each other in the whole physical region. For the $B\toπ$ transition form factor in the large recoil regions, one can apply the PQCD approach, where the transverse momentum dependence for both the hard scattering part and the non-perturbative wavefunction, the Sudakov effects and the threshold effects are included to regulate the endpoint singularity and to derive a more reliable PQCD result. Pionic twist-3 contributions are carefully studied with a better endpoint behavior wavefunction for $Ψ_p$ and we find that its contribution is less than the leading twist contribution. Both the two wavefunctions $Ψ_B$ and $\barΨ_B$ of the B meson can give sizable contributions to the $B\toπ$ transition form factor and should be kept for a better understanding of the B decays. The present obtained PQCD results can match with both the QCD light-cone sum rule results and the extrapolated lattice QCD results in the large recoil regions.

hep-ph↗