arXiv subjects

Ho-Meoyng Choi

Publications and source records attributed to Ho-Meoyng Choi.

At least 55 records · Page 3Linked to original sources

arXiv2011

Light-front zero-mode contribution to the tensor form factors for the exclusive rare $P\to V\ell^+\ell^-$ decays

We study the light-front zero-mode contribution to the tensor form factors $T_i(i=1,2,3)$ for the exclusive rare $P\to V\ell^+\ell^-$ decays using a covariant fermion field theory model in $(3+1)$ dimensions. While the zero-mode contribution in principle depends on the form of the vector meson vertex $Γ^μ=γ^μ- (2k-P_V)^μ/D$, the three tensor form factors $T_i(i=1,2,3)$ are found to be free from the zero mode if the denominator $D$ contains the term proportional to the light-front energy or the longitudinal momentum fraction factor $(1/x)^n$ of the struck quark with the power $n>0$. Since the denominator $D$ used in the light-front quark model (LFQM) has the power $n=1/2$, the three tensor form factors $T_i(i=1,2,3)$ can be computed in LFQM safely without involving any complicate zero-mode contribution. The lack of zero-mode contribution benefits the phenomenology with LFQM.

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arXiv2010

Exclusive rare $B_s\to (K,η,η')\ell^+\ell^-$ decays in the light-front quark model

Using the light-front quark model, we calculate the transition form factors, decay rates, and longitudinal lepton polarization asymmetries for the exclusive rare $B_s\to (K,η^{(\prime)})(\ell^+\ell^-,ν_{\ell}\bar{ν_{\ell}}$ ($\ell=e,μ,τ$) decays within the standard model, taking into account the $η-η'$ mixing angle. For the mixing angle $θ=-20^{\circ}$ ($-10^{\circ}$) in the octet-singlet basis, we obtain ${\rm BR}(B_s\to η\sumν_{\ell}\barν_{\ell})=1.1 (1.7)\times 10^{-6}$, ${\rm BR}(B_s\to ημ^+μ^-)=1.5 (2.4)\times 10^{-7}$, ${\rm BR}(B_s\to ητ^+τ^-)=3.8 (5.8)\times 10^{-8}$, ${\rm BR}(B_s\to η'\sumν_{\ell}\barν_{\ell})=1.8 (1.3)\times 10^{-6}$, ${\rm BR}(B_s\to η'μ^+μ^-)=2.4 (1.8)\times 10^{-7}$, and ${\rm BR}(B_s\to η'τ^+τ^-)=3.4 (2.6)\times 10^{-8}$, respectively. The branching ratios for the $B_s\to K(ν_{\ell}\bar{ν_{\ell}},\ell^+\ell^-)$ decays are at least an order of magnitude smaller than those for the $B_s\to η^{(\prime)}(ν_{\ell}\bar{ν_{\ell}},\ell^+\ell^-)$ decays. The averaged values of the lepton polarization asymmetries for $B_s\to (K,η^{(\prime)})\ell^+\ell^-$ are obtained as $\la P^K_L\ra_μ=\la P^η_L\ra_μ=\la P^{η'}_L\ra_μ=-0.98$, $\la P^K_L\ra_τ=-0.24$, $\la P^η_L\ra_τ=-0.20$ and $\la P^{η'}_L\ra_τ=-0.14$, respectively.

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arXiv2010

Light-front quark model analysis of the exclusive rare $B_c\to D_{(s)}(\ell^+\ell^-,ν_{\ell}\barν_{\ell})$ decays

We investigate the exclusive rare $B_c\to D_{(s)}ν_{\ell}\bar{ν_{\ell}}$ and $B\to D_{(s)}\ell^+\ell^-$ ($\ell=e,μ,τ$) decays within the standard model and the light-front quark model constrained by the variational principle for the QCD motivated effective Hamiltonian. The form factors $f_{\pm}(q^2)$ and $f_T(q^2)$ are obtained from the analytic continuation method in the $q^+=0$ frame. While the form factors $f_+(q^2)$ and $f_T(q^2)$ are free from the zero-mode, the form factor $f_-(q^2)$ is not free from the zero-mode in the $q^+=0$ frame. We discuss the covariance(i.e. frame-independence) of our model calculation and quantify the zero-mode contributions to $f_-(q^2)$ for $B_c\to D_{(s)}$ decays. The branching ratios and the longitudinal lepton polarization asymmetries are calculated with and without the long-distance contributions. Our numerical results for the non-resonant branching ratios for $B_c\to D(D_s)\sumν_{\ell}\bar{ν_{\ell}}$ and $B_c\to D(D_s)\ell^+\ell^-$ are in the order of $10^{-8} (10^{-7})$ and $10^{-9} (10^{-8})$, respectively. The averaged values of the lepton polarization asymmetries obtained from the linear (harmonic oscillator) potential parameters are found to be $-0.99 (-0.99)$ for $B_c\to Dμ^+μ^-$ and $-0.16 (-0.15)$ for $B_c\to Dτ^+τ^-$, and $-0.98 (-0.98)$ for $B_c\to D_sμ^+μ^-$ and $-0.14 (-0.12)$ for $B_c\to D_sτ^+τ^-$, respectively.

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arXiv2009

Non-leptonic two-body decays of the Bc meson in light-front quark model and QCD factorization approach

We study exclusive non-leptonic two-body $B_c\to(D_{(s)},η_c,B_{(s)})+F$ decays with $F$(pseudoscalar or vector meson) being factored out in QCD factorization approach. The non-leptonic decay amplitudes are related to the product of meson decay constants and the form factors for semileptonic $B_c$ decays. As inputs in obtaining the branching ratios for a large set of non-leptonic $B_c$ decays, we use the weak form factors for the semileptonic $B_c\to(D_{(s)},η_c,B_{(s)})$ decays in the whole kinematical region and the unmeasured meson decay constants obtained from our previous light-front quark model. We compare our results of the branching ratios with those of other theoretical studies.

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arXiv2009

Semileptonic and radiative decays of the B_c meson in light-front quark model

We investigate the exclusive semileptonic $B_c\to (D,η_c,B,B_s)\ellν_\ell$, $η_b\to B_c\ellν_\ell$($\ell=e,μ,τ$) decays using the light-front quark model constrained by the variational principle for the QCD motivated effective Hamiltonian. The form factors $f_+(q^2)$ and $f_-(q^2)$ are obtained from the analytic continuation method in the $q^+=0$ frame. While the form factor $f_+(q^2)$ is free from the zero-mode, the form factor $f_-(q^2)$ is not free from the zero-mode in the $q^+=0$ frame. We quantify the zero-mode contributions to $f_-(q^2)$ for various semileptonic $B_c$ decays. Using our effective method to relate the non-wave function vertex to the light-front valence wave function, we incorporate the zero-mode contribution as a convolution of zero-mode operator with the initial and final state wave functions. Our results are then compared to the available experimental data and the results from other theoretical approaches. Since the prediction on the magnetic dipole $B^*_c\to B_c+γ$ decay turns out to be very sensitive to the mass difference between $B^*_c$ and $B_c$ mesons, the decay width $Γ(B^*_c \to B_c γ)$ may help in determining the mass of $B^*_c$ experimentally. Furthermore, we compare the results from the harmonic oscillator potential and the linear potential and identify the decay processes that are sensitive to the choice of confining potential. From the future experimental data on these sensitive processes, one may obtain more realistic information on the potential between quark and antiquark in the heavy meson system.

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arXiv2008

Conformal Symmetry and Pion Form Factor: Space- and Time-like Region

We extend a recent analysis of the pion electromagnetic form factor constrained by the conformal symmetry to explore the time-like region. We show explicitly that the time-like form factor obtained by the analytic continuation of the space-like form factor correctly satisfies the dispersion relation. Our results indicate that the quark spin and dynamical mass effects are crucial to yield the realistic features of the vector meson dominance phenomena.

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arXiv2008

Space- and time-like form factors for $ω\toπγ^$ and $K^\to Kγ^*$ in light-front quark model

We investigate space- and time-like form factors for $ω\toπγ^*$ and $K^*\to Kγ^*$ decays using the light-front quark model constrained by the variational principle for the QCD-motivated effective Hamiltonian. The momentum dependent space-like form factors are obtained in the $q^+=0$ frame and then analytically continued to the time-like region. Our prediction for the time-like form factor $F_{ωπ}(q^2)$ is in good agreement with the experimental data. We also find that the space-like form factor $F_{K^{*\pm}K^{\pm}}(Q^2)$ for charged kaons encounters a zero because of the negative interference between the two currents to the quark and the antiquark.

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arXiv2007

Perturbative QCD analysis of exclusive J/ψ+η_c production in e^+e^- annihilation

We analyze the exclusive charmonium $J/ψ+η_c$ pair production in $e^+e^-$ annihilation using the nonfactorized perturbative QCD and the light-front quark model(LFQM) that goes beyond the peaking approximation. We effectively include all orders of higher twist terms in the leading order of QCD coupling constant and compare our nonfactorized analysis with the usual factorized analysis in the calculation of the cross section. We also calculate the quark distribution amplitudes, the Gegenbauer moments, and the decay constants for $J/ψ$ and $η_c$ mesons using our LFQM. Our nonfactorized result enhances the NRQCD result by a factor of $3\sim4$ at $\sqrt{s}=10.6$ GeV.

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arXiv2007

Light-front quark model analysis of heavy meson radiative decays

We present the magnetic dipole($M1$) transitions $V\to Pγ$ of various heavy-flavored mesons such as $(D,D^*,D_s,D^{*}_s,η_c, J/ψ)$ and $(B,B^*,B_s,B^*_s,η_b,Υ)$ using the light-front quark model constrained by the variational principle for the QCD-motivated effective Hamiltonian. The weak decay constants of heavy mesons and the decay widths for $V\to Pγ$ are calculated. The radiative decay for $Υ\toη_{b}γ$ process is found to be very helpful to determine the unmeasured mass of $η_b$. Our numerical results are overall in good agreement with the available experimental data as well as other theoretical model calculations.

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arXiv2007

Decay constants and radiative decays of heavy mesons in light-front quark model

We investigate the magnetic dipole decays $V\to Pγ$ of various heavy-flavored mesons such as $(D,D^*,D_s,D^{*}_s,η_c, J/ψ)$ and $(B,B^*,B_s,B^*_s,η_b,Υ)$ using the light-front quark model constrained by the variational principle for the QCD-motivated effective Hamiltonian. The momentum dependent form factors $F_{VP}(q^2)$ for $V\to Pγ^*$ decays are obtained in the $q^+=0$ frame and then analytically continued to the timelike region by changing ${\bf q}_\perp$ to $i{\bf q}_\perp$ in the form factors. The coupling constant $g_{VPγ}$ for real photon case is then obtained in the limit as $q^2\to 0$, i.e. $g_{VPγ}=F_{VP}(q^2=0)$. The weak decay constants of heavy pseudoscalar and vector mesons are also calculated. Our numerical results for the decay constants and radiative decay widths for the heavy-flavored mesons are overall in good agreement with the available experimental data as well as other theoretical model calculations.

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arXiv2007

Distribution amplitudes and decay constants for $(π,K,ρ,K^*)$ mesons in light-front quark model

We present a calculation of the quark distribution amplitudes(DAs), the Gegenbauer moments, and decay constants for $π,ρ,K$ and $K^*$ mesons using the light-front quark model. While the quark DA for $π$ is somewhat broader than the asymptotic one, that for $ρ$ meson is very close to the asymptotic one. The quark DAs for $K$ and $K^*$ show asymmetric form due to the flavor SU(3)-symmetry breaking effect. The decay constants for the transversely polarized $ρ$ and $K^*$ mesons($f^T_ρ$ and $f^T_{K^*}$) as well as the longitudinally polarized ones($f_ρ$ and $f_{K^*}$) are also obtained. Our averaged values for $f^T_V/f_V$, i.e. $(f^T_ρ/f_ρ)_{\rm av}=0.78$ and $(f^T_{K^*}/f_{K^*})_{\rm av}=0.84$, are found to be consistent with other model predictions. Especially, our results for the decay constants are in a good agreement with the SU(6) symmetry relation, $f^T_{ρ(K^*)}=(f_{π(K)}+f_{ρ(K^*)})/2$.

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arXiv2006

New Developments in Treacherous Points of Light-Front Dynamics

Light-front dynamics(LFD) plays an important role in hadron phenomenology. Last few years, however, it has been emphasized that treacherous points such as zero-mode contributions should be taken into account for successful LFD applications to hadron phenomenology. We discuss examples of treacherous points and present new progresses made last few years to handle them correctly.

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arXiv2006

{PQCD analysis of exclusive $e^+e^-\to D_{[s]}^+D_{[s]}^-$ cross section at $\sqrt{s}=10.6$ GeV

We analyze the exclusive pseudoscalar $D_{[s]}^+D_{[s]}^-$ pair production in $e^+e^-$ annihilations at $\sqrt{s}=10.6$ GeV using a non-factorized PQCD with the light-front wave function that goes beyond the peaking approximation. We compare our non-factorized analysis with the usual factorized analysis based on the peaking approximation in the calculation of the cross section for the heavy meson pair production. We also discuss the higher helicity contribution to the cross section. Our analysis provides a constraint on the size of quark transverse momentum inside the $D$ meson from the recent Belle data, $σ_{\rm Exp.}(e^+e^-\to D^+D^-)<0.04$.

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arXiv2005

Revealing treacherous points for successful light-front phenomenological applications

Light-front dynamics(LFD) plays an important role in hadron phenomenology as evidenced from recent development of generalized parton distributions and other quantities involving hadrons. For successful LFD applications to hadron phenomenology, however, treacherous points such as zero-mode contributions should be taken into account. For a concrete example of zero-mode contribution, we present Standard Model analysis of vector anomaly in the CP-even form factors of W^{\pm} gauge bosons. Main distinguished features of LFD is discussed in comparison with other Hamiltonian dynamics. We also present a power counting method to correctly pin down which hadron form factors receive the zero-mode contribution and which ones do not. Indications from our analysis to hadron phenomenology are discussed.

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arXiv2005

The Light-Front Zero-Mode Contribution to the Good Current in Weak Transition

We examine the light-front zero-mode contribution to the good(+) current matrix elements between pseudoscalar and vector mesons. In particular, we discuss the transition form factor $f(q^2)$ which has been suspected to have the light-front zero-mode contribution. While the zero-mode contribution in principle depends on the form of the vector meson vertex $Γ^μ=γ^μ- (P_V -2k)^μ/D$, the form factor $f(q^2)$ is found to be free from the zero-mode contribution if the denominator $D$ contains the term proportional to the light-front energy $(k^-)^{n}$ with the power $n>0$. The lack of zero-mode contribution benefits the light-front quark model phenomenology. We present our numerical calculations for the $B\toρ$ transition.

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arXiv2004

Electromagnetic Structure of the $ρ$ Meson in the Light-Front Quark Model

We investigate the elastic form factors of the rho meson in the light-front quark model(LFQM). With the phenomenologically accessible meson vertices including the one obtained by the Melosh transformation frequently used in the LFQM, we find that only the helicity $0\to 0$ matrix element of the plus current receives the zero-mode contribution. We quantify the zero-mode contribution in the helicity $0\to 0$ amplitude using the angular condition of spin-1 system. After taking care of the zero-mode issue, we obtain the magnetic($μ$) and quadrupole($Q$) moments of the rho meson as $μ=1.92$ and $Q=0.43$, respectively, in the LFQM consistent with the Melosh transformation and compare our results with other available theoretical predictions.

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arXiv2003

Radiative Scalar Meson Decays in the Light-Front Quark Model

We construct a relativistic $^3P_0$ wavefunction for scalar mesons within the framework of light-front quark model(LFQM). This scalar wavefunction is used to perform relativistic calculations of absolute widths for the radiative decay processes$(0^{++})\toγγ,(0^{++})\toϕγ$, and $(0^{++})\toργ$ which incorporate the effects of glueball-$q\bar{q}$ mixing. The mixed physical states are assumed to be $f_0(1370),f_0(1500)$,and $f_0(1710)$ for which the flavor-glue content is taken from the mixing calculations of other works. Since experimental data for these processes are poor, our results are compared with those of a recent non-relativistic model calculation. We find that while the relativistic corrections introduced by the LFQM reduce the magnitudes of the decay widths by 50-70%, the relative strengths between different decay processes are fairly well preserved. We also calculate decay widths for the processes $ϕ\to(0^{++})γ$ and $(0^{++})\toγ\gamm$ involving the light scalars $f_0(980)$ and $a_0(980)$ to test the simple $q\bar{q}$ model of these mesons. Our results of $q\bar{q}$ model for these processes are not quite consistent with well-established data, further supporting the idea that $f_0(980)$ and $a_0(980)$ are not conventional $q\bar{q}$ states.

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arXiv2003

Bubble collisions in a SU(2) model of QCD

Starting from the QCD action in an instanton-like SU(2) Yang-Mills field theory, we derive equations of motion in Minkowski space. Possible bubble collisions are studued in a (1+1)-dimension reduction . We find gluonic structures like interior walls, which might give rise to CMBR effects.

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