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Kwei-Chou Yang

Publications and source records attributed to Kwei-Chou Yang.

At least 37 records · Page 2Linked to original sources
arXiv2011

Modified Padé Approach to the S-Wave Charmonium Spectroscopy in QCD

We calculate the $S$-wave charmonium spectroscopy using the Hamiltonian with the non-relativistic QCD (NRQCD) potential. The logarithmic factor $\ln μr$, appearing in the next-to-leading order QCD loop corrections to the potential, is expanded about $r=1/μ$, where $μ$ corresponds to the typical charmonium scale. The resulting potential characterized by the Coulombic and linear components is consistent with the form of the Cornell potential. We obtain $χ^2$ fitting results for the masses of the $S$-wave charmonium states, $η_c(1^1S_0)$, $J/ψ(1^3S_1)$, $η_c(2^1S_0)$, and $ψ(2^3S_1)$ in remarkable accordance with data. Our results successfully account for the hyperfine splitting for the 1S state as well as for the 2S state. We further use the three best fit parameters: the charm quark mass $m_c$, coupling constant $α_s$ and the corresponding scale $μ$ to predict the $S$-wave mass spectrum with $n\leq 6$. The hints for results are discussed.

hep-ph↗
arXiv2011

Charmless Hadronic B Decays into a Tensor Meson

Two-body charmless hadronic B decays involving a tensor meson in the final state are studied within the framework of QCD factorization (QCDF). Due to the G-parity of the tensor meson, both the chiral-even and chiral-odd two-parton light-cone distribution amplitudes of the tensor meson are antisymmetric under the interchange of momentum fractions of the quark and anti-quark in the SU(3) limit. Our main results are: (i) In the naive factorization approach, the decays such as $B^-\to \bar K_2^{*0}π^-$ and $\bar B^0\to K_2^{*-}π^+$ with a tensor meson emitted are prohibited owing to the fact that a tensor meson cannot be created from the local V-A or tensor current. Nevertheless, they receive nonfactorizable contributions in QCDF from vertex, penguin and hard spectator corrections. The experimental observation of $B^-\to \bar K_2^{*0}π^-$ indicates the importance of nonfactorizable effects. (ii) For penguin-dominated $B\to TP$ and $TV$ decays, the predicted rates in naive factorization are usually too small by one to two orders of magnitude. In QCDF, they are enhanced by power corrections from penguin annihilation and nonfactorizable contributions.(iii) The dominant penguin contributions to $B\to K_2^*η^{(')}$ arise from the processes: (a) $b\to ss\bar s\to sη_s$ and (b) $b\to s q\bar q\to q \bar K_2^*$ with $η_q=(u\bar u+d\bar d)/\sqrt{2}$ and $η_s=s\bar s$. The interference, constructive for $K_2^*η'$ and destructive for $K_2^*η$, explains why $Γ(B\to K_2^*η')\ggΓ(B\to K_2^*η)$.

hep-ph↗
arXiv2010

Perturbations in Matter Bounce with Non-minimal Coupling

In this paper, we investigate the perturbations in matter bounce induced from Lee-Wick lagrangian with the involvement of non-minimal coupling to the Einstein Gravity. We find that this extra non-minimal coupling term can cause a red-tilt on the primordial metric perturbation at extremely large scales. It can also lead to large enhancement of reheating of the normal field particles compared to the usual minimal coupling models.

astro-ph.CO↗
arXiv2010

B to Light Tensor Meson Form Factors Derived from Light-Cone Sum Rules

Using the recent results for the two-parton light-cone distribution amplitudes of the tensor meson, we calculate the form factors for the decays of $B_{u,d,s}$ into the light $J^{PC}=2^{++}$ tensor mesons via the vector/axial-vector/tensor current with the light-cone sum rules. We also obtain the $q^2$-dependence of the form factors.

hep-ph↗
arXiv2010

Form Factors of $B_{u,d,s}$ Decays into P-Wave Axial-Vector Mesons in the Light-Cone Sum Rule Approach

We calculate the vector and axial-vector form factors of $B_{u,d,s}$ decays into P-wave axial-vector mesons in the light-cone sum rule approach. For the sum rule results, we have included corrections of order $m_A/m_b$, where $m_A$ is the mass of the axial-vector meson $A$. The results are relevant to the light-cone distribution amplitudes of the axial-vector mesons. It is important to note that, owing to the $G$-parity, the chiral-even two-parton light-cone distribution amplitudes of the $^3P_1$ ($^1P_1$) mesons are symmetric (antisymmetric) under the exchange of quark and anti-quark momentum fractions in the SU(3) limit. For chiral-odd light-cone distribution amplitudes, it is the other way around. The predictions for decay rates of $B_{u,d,s} \to A e ν_e$ are also presented.

hep-ph↗
arXiv2010

Light-Cone Distribution Amplitudes of Axial-vector Mesons

We have presented a detailed study of twist-2 and twist-3 light-cone distribution amplitudes of $1^3P_1$ and $1^1P_1$ axial-vector mesons, based on QCD conformal partial wave expansion. Applying equations of motion, the twist-three two-parton light-cone distribution amplitudes can be expressed in terms of leading-twist and twist-three three-parton light-cone distribution amplitudes. The relevant G-parity invariant and violating parameters, containing the corrections due to the SU(3) breaking effects, are evaluated from the QCD sum rule method. The results for axial-vector decay constants of $1^3P_1$ states are presented. The values of tensor decay constants and Gegenbauer moments of the leading twist distribution amplitudes for $1^1P_1$ states are updated. Using Gell-Mann-Okubo mass formula, the mixing angle for the $f_8$ and $f_1$ of $1^3P_1$ states is $θ_{^3P_1}\sim 38^\circ$, and that for $h_8$ and $h_1$ of $1^1P_1$ states is $θ_{^1P_1}\sim 10^\circ$. The detailed properties for physical states $f_1(1285), f_1(1420), h_1(1170)$, and $h_1(1380)$ are given. Assuming the mixing angle between $K_{1A}$ and $K_{1B}$ to be $θ_K=45^\circ$ or $-45^\circ$, we also give the detailed study for $K_1(1270)$ and $K_1(1400)$. Using the conformal partial wave expansion, we obtain the models for light-cone distribution amplitudes, containing contributions up to conformal spin 9/2. It is interesting to note that some distribution amplitudes have significant asymmetric behaviors, which should be phenomenologically attractive.

hep-ph↗
arXiv2010

Two-parton Light-cone Distribution Amplitudes of Tensor Mesons

We present a detailed study of the two-parton light-cone distribution amplitudes for $1\,^3P_2$ nonet tensor mesons. The asymptotic two-parton distribution amplitudes of twist-2 and twist-3 are given. The decay constants $f_T$ and $f_T^\bot$ defined by the matrices of non-local operators on the lightcone are estimated using the QCD sum rule techniques. We also study the decay constants for $f_2(1270)$ and $f_2^\prime(1525)$ based on the hypothesis of tensor meson dominance together with the data of $Γ(f_2\to ππ)$ and $Γ(f'_2\to K\bar K)$ and find that the results are in accordance with the sum rule predictions.

hep-ph↗
arXiv2010

Radiative and Semileptonic B Decays Involving Higher K-Resonances in the Final States

We study the radiative and semileptonic B decays involving a spin-$J$ resonant $K_J^{(*)}$ with parity $(-1)^J$ for $K_J^*$ and $(-1)^{J+1}$ for $K_J$ in the final state. Using the large energy effective theory (LEET) techniques, we formulate $B \to K_J^{(*)}$ transition form factors in the large recoil region in terms of two independent LEET functions $ζ_\perp^{K_J^{(*)}}$ and $ζ_\parallel^{K_J^{(*)}}$, the values of which at zero momentum transfer are estimated in the BSW model. According to the QCD counting rules, $ζ_{\perp,\parallel}^{K_J^{(*)}}$ exhibit a dipole dependence in $q^2$. We predict the decay rates for $B \to K_J^{(*)} γ$, $B \to K_J^{(*)} \ell^+ \ell^-$ and $B \to K_J^{(*)}ν\barν$. The branching fractions for these decays with higher $K$-resonances in the final state are suppressed due to the smaller phase spaces and the smaller values of $ζ^{K_J^{(*)}}_{\perp,\parallel}$. Furthermore, if the spin of $K_J^{(*)}$ becomes larger, the branching fractions will be further suppressed due to the smaller Clebsch-Gordan coefficients defined by the polarization tensors of the $K_J^{(*)}$. We also calculate the forward backward asymmetry of the $B \to K_J^{(*)} \ell^+ \ell^-$ decay, for which the zero is highly insensitive to the $K$-resonances in the LEET parametrization.

hep-ph↗
arXiv2009

Radiative and Semileptonic B Decays Involving the Tensor Meson K_2^*(1430) in the Standard Model and Beyond

We study semileptonic and radiative B decays involving the strange tensor meson K_2^*(1430) in the final state. Using the large energy effective theory (LEET) techniques, we formulate the B \to K_2^* transition form factors in large recoil region. All the form factors can be parametrized in terms of two independent LEET parameters ζ_\perp and ζ_\parallel. The magnitude of ζ_\perp is estimated from the data for Br(B \to K_2^*(1430)γ). Assuming a dipole q^2-dependence for the LEET parameters and ζ_\parallel/ζ_\perp = 1.0 \pm 0.2, we investigate the decays B \to K_2^* \ell^+ \ell^- and B \to K_2^* ν\barν, where the contributions due to $ζ_\parallel are suppressed by m_{K_2^*}/m_B. For the B \to K_2^* \ell^+ \ell^- decay, in the large recoil region where the hadronic uncertainties are considerably reduced, the longitudinal distribution d F_L/ds is reduced by 20-30 % due to the flipped sign of c_7^eff compared with the standard model result. Moreover, the forward-backward asymmetry zero is about 3.4 GeV^2 in the standard model, but changing the sign of c_7^eff yields a positive asymmetry for all values of the invariant mass of the lepton pair. We calculate the branching fraction for B \to K_2^* ν\barν in the standard model. Our result exhibits the impressed resemblance between B \to K_2^*(1430) \ell^+\ell^-, ν\barν and B \to K^*(892) \ell^+ \ell^-, ν\barν.

hep-ph↗
arXiv2008

Properties of Axial-vector Mesons and Charmless B Decays: B -> VV, VA, AA

I introduce the properties of the light axial-vector mesons. The branching ratios, longitudinal fractions and direct CP asymmetries of the related charmless two-body B decays into final states involving two axial-vector mesons ($AA$) or one vector and one axial-vector meson ($VA$) are discussed within the framework of QCD factorization.

hep-ph↗
arXiv2008

Branching Ratios and Polarization in B-> VV,VA,AA Decays

We present a detailed study of charmless two-body B decays into final states involving two vector mesons (VV) or two axial-vector mesons (AA) or one vector and one axial-vector meson (VA), within the framework of QCD factorization, where $A$ is either a $^3P_1$ or $^1P_1$ axial-vector meson. The main results are as follows. (i) In the presence of NLO nonfactorizable corrections, effective Wilson coefficients $a_i^h$ are helicity dependent. For some penguin-dominated modes, the constructive (destructive) interference in the negative-helicity (longitudinal-helicity) amplitude of the $B\to VV$ decay will render the former comparable to the latter and push up the transverse polarization. (ii) In QCD factorization, the transverse polarization fraction can be large for penguin-dominated charmless $VV$ modes by allowing for sizable penguin annihilation contributions. (iii) Using the measured $\bar K^{*0}ρ^-$ channel as an input, we predict the branching ratios and polarization fractions for other $\ov B\to \bar K^*ρ$ decays. (iv) The smallness of the axial-vector decay constant of the $^1P_1$ axial vector meson can be tested by measuring various $b_1ρ$ modes to see if $Γ(\bar B^0\to b_1^-ρ^+)\ll Γ(\bar B^0\to b_1^+ρ^-)$ and $Γ(B^-\to b_1^-ρ^0)\ll Γ(B^-\to b_1^0ρ^-)$. (v) For the penguin-dominated modes $a_1K^*$ and $b_1K^*$, it is found that the former are dominated by transverse polarization amplitudes, whereas the latter are governed by longitudinal polarization states.

hep-ph↗
arXiv2008

K1(1270)-K1(1400) Mixing Angle and New-Physics Effects in B to K1 l+ l- Decays

We study semileptonic B meson decays B to K_1(1270) l^+ l^- and K_1(1400) l^+ l^- (l=e, mu, tau), where the strange P-wave mesons, K_1(1270) and K_1(1400), are the mixtures of the K_{1A} and K_{1B}, which are the 1^3P_1 and 1^1P_1 states, respectively. We show that the ratio R_l = Br(B to K_1(1400) l^+ l^-)/Br(B to K_1(1270) l^+ l^-), insensitive to new-physics parameters, is suitable for determining the K_1(1270)-K_1(1400) mixing angle, theta_{K_1}. The forward-backward asymmetry shows a weak theta_{K_1}-dependence for B to K_1(1270) mu^+ mu^-, but relatively strong for B to K_1(1400) mu^+ mu^-. We investigate model-independent new-physics corrections to operators relevant to the b to s l^+ l^- electroweak-penguin and weak-box diagrams. Furthermore, for the B to K_1(1270) mu^+ mu^- decay the position of the forward-backward asymmetry zero, which is almost independent of the value of theta_{K_1}, can be dramatically changed under variation of new-physics parameters.

hep-ph↗
arXiv2008

$B \to K_1 γ$ Decays in the Light-Cone QCD Sum Rules

We present a detailed study of $B\to K_1(1270) γ$ and $B\to K_1(1400) γ$ decays. Using the light-cone sum rule technique, we calculate the $B\to K_{1A} (1^3P_1)$ and $B\to K_{1B} (1^1P_1)$ tensor form factors, $T_1^{K_{1A}}(0)$ and $T_1^{K_{1B}}(0)$, where the contributions are included up to the first order in $m_{K_1}/m_b$. We resolve the sign ambiguity of the $K_1(1270)$--$K_1(1400)$ mixing angle $θ_{K_1}$ by defining the signs of decay constants, $f_{K_{1A}}$ and $f_{K_{1B}}^\perp$. From the comparison of the theoretical calculation and the data for decays $B\to K_1 γ$ and $τ^-\to K_1^-(1270)ν_τ$, we find that $θ_{K_1}=-(34\pm 13)^\circ$ is favored. In contrast to $B\to K^* γ$, the hard-spectator contribution suppresses the $B\to K_1(1270) γ$ and $B\to K_1(1400) γ$ branching ratios slightly. The predicted branching ratios are in agreement with the Belle measurement within the errors. We point out that a more precise measurement for the ratio $R_{K_1}={\cal B}(B\to K_1(1400)γ)/{\cal B}(B\to K_1(1270)γ)$ can offer a better determination for the $θ_{K_1}$ and consequently the theoretical uncertainties can be reduced.

hep-ph↗
arXiv2008

(Pseudo-) Scalar Operators in the MSSM and B to phi K^*, K eta(') Decays

We study the effect of b to s sbar s scalar/pseudoscalar operators, originating from penguin diagrams of neutral Higgs bosons in the MSSM, in B to K eta(') and B to phi K^* decays. These operators can be Fierz-transformed into tensor operators, and the resultant tensor operators could affect the transverse polarization amplitudes in B to phi K^* decays. We find that only when the weak annihilations in B to phi K^* into account, the polarization puzzle can be resolved, so that new physics effects are strongly suppressed and no more relevant to the enhancement of the transverse modes in B to phi K^* decays.

hep-ph↗
arXiv2007

Pseudoscalar and Scalar Operators of Higgs-Penguins in the MSSM and B to phi K^*, K eta(') Decays

We study the effect of b to s sbar s scalar/pseudoscalar operators in B to K eta('), phi K^* decays. In the minimal supersymmetric standard model (MSSM), such scalar/pseudoscalar operators can be induced by the penguin diagrams of neutral Higgs bosons. These operators can be Fierz-transformed into tensor operators, and the resultant tensor operators could affect the transverse polarization amplitudes in B to phi K^* decays. A combined analysis of the decays B to phi K^* and B to K eta('), including b to s sbar s scalar/pseudoscalar operators and their Fierz-transformed tensor operators originated from the MSSM, is performed. Our study is based on the followings: (1) Assuming that weak annihilations in B to phi K^* is negligible and the polarization puzzle is resolved by Fierz-transformed tensor operators, it results in too large coefficients of scalar/pseudoscalar operators, such that the resulting B to K eta(') branching fractions are much larger than observations. (2) When we take the weak annihilations in B to phi K^* into account, the polarization puzzle can be resolved. In this case, new physics effects are strongly suppressed and no more relevant to the enhancement of the transverse modes in B to phi K^* decays.

hep-ph↗
arXiv2007

Indications of the possible observation of the lowest-lying 1^{-+} QCD state

We discuss properties of 1^{-+} exotic mesons within the framework of the QCD field-theoretic approach. We estimate the mass of the lowest-lying 1^{-+} exotic meson using renormalization-improved QCD sum rules, and find that the mass lies around $1.26\pm 0.15$ GeV, in good agreement with the $π_1(1400)$ data. This state should be expected in QCD. We find that the mass for the lowest-lying strange 1^{-+} meson is $1.31\pm 0.19$ GeV. Our result hints that the K^*(1410) may be the lowest-lying 1^{-+} nonet state.

hep-ph↗
arXiv2007

Hadronic charmless B decays B-> AP

The two-body hadronic decays of B mesons into pseudoscalar and axial vector mesons are studied within the framework of QCD factorization. The light-cone distribution amplitudes (LCDAs) for $^3P_1$ and $^1P_1$ axial-vector mesons have been evaluated using the QCD sum rule method. Owing to the G-parity, the chiral-even two-parton light-cone distribution amplitudes of the $^3P_1$ ($^1P_1$) mesons are symmetric (antisymmetric) under the exchange of quark and anti-quark momentum fractions in the SU(3) limit. For chiral-odd LCDAs, it is other way around. The main results are the following: (i) The predicted rates for $a_1^\pm(1260)π^\mp$, $b_1^\pm(1235)π^\mp$, $b_1^0(1235)π^-$, $a_1^+K^-$ and $b_1^+K^-$ modes are in good agreement with the data. However, the naively expected ratios $Br(B^-\to a_1^0π^-)/Br(\ov B^0\to a_1^+π^-)\leq 1$, $Br(B^-\to a_1^-π^0)/Br(\ov B^0\to a_1^-π^+)\sim {1\over 2}$ and $Br(B^-\to b_1^0K^-)/Br(\ov B^0\to b_1^+K^-)\sim {1\over 2}$ are not borne out by experiment. This should be clarified by the improved measurements of these decays. (ii) Since the $\bar B\to b_1K$ decays receive sizable annihilation contributions, their rates are sensitive to the interference between penguin and annihilation terms. The measurement of $Br(\bar B^0\to b_1^+K^-)$ implies a destructive interference which in turn indicates that the form factors for $B\to b_1$ and $B\to a_1$ transitions are of opposite signs. (iii) Sizable power corrections such as weak annihilation are needed to account for the observed rates of the penguin-dominated modes $K_1^-(1270)π^+$ and $K_1^-(1400)π^+$.

hep-ph↗