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Kuang-Ta Chao

Publications and source records attributed to Kuang-Ta Chao.

At least 91 records · Page 5Linked to original sources
arXiv2003

Problems of Double Charm Production in $e^+e^-$ Annihilation at $\sqrt{s}=10.6$ GeV

Using the nonrelativistic QCD(NRQCD) factorization formalism, we calculate the color-singlet cross sections for exclusive production processes ${e^++e^-\to J/ψ+η_c}$~ and ~$e^++e^-\to J/ψ+ χ_{cJ}$~$(J=0,1,2)$ at the center-of-mass energy $\sqrt{s}$=10.6 GeV. The cross sections are estimated to be 5.5fb, 6.7fb, 1.1fb, and 1.6fb for $η_c, χ_{c0}, χ_{c1}$ and $χ_{c2}$, respectively. The calculated $J/ψ+η_c$ production rate is smaller than the recent Belle data by about an order of magnitude, which might indicate the failure of perturbative QCD calculation to explain the double-charmonium production data. The complete $\cal{O}$$(α^2_{s})$ color-singlet cross section for ${e^++e^-\to χ_{c0}+ c\bar {c}}$ is calculated. In addition, we also evaluate the ratio of exclusive to inclusive production cross sections. The ratio of $J/ψη_c$ production to $J/ψc\bar{c}$ production could be consistent with the experimental data.

hep-ph↗
arXiv2002

B ->η_c K(η_c^\prime K) decays in QCD factorization

We study the exclusive decays of $B$ meson into pseudoscalar charmonium states $η_c$ and $η_c^\prime$ within the QCD factorization approach and find that the nonfactorizable corrections to naive factorization are infrared safe at leading-twist order. The spectator interactions arising from the kaon twist-3 effects are formally power-suppressed but chirally and logarithmically enhanced. The theoretical decay rates are too small to accommodate the experimental data. On the other hand, we compare the theoretical calculations for $J/ψ, ψ^\prime$, and $η_c, η_c^\prime$, and find that the predicted relative decay rates of these four states are approximately compatible with experimental data.

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arXiv2002

D-wave Charmonium Production in $e^+e^-$ Annihilation at $\sqrt{s}=10.6$ GeV

We calculate the D-wave charmonium production in $e^+e^-$ annihilation at BELLE and BABAR at $\sqrt{s}=10.6$ GeV using the nonrelativistic QCD factorization formalism, including color singlet and color octet contributions. We analyze the contributions of various processes for $δ_J(J=1,2)$ production. We find that both the color singlet and color octet channels may give substantial contributions, and the production rates are estimated to be $σ(δ_1)\simeq 0.043-0.16pb$ and $σ(δ_2)\simeq 0.094-0.29pb$, which, however, are very sensitive to the choice of the color octet matrix elements of the D-wave charmonium states. The measurement of D-wave charmonium production at BABAR and BELLE in the future will be very helpful to test the color octet mechanism and to determine the color octet matrix elements.

hep-ph↗
arXiv2002

Charmonium Production in $e^+e^-$ Annihilation at $\sqrt{s}=10.6GeV$

We review the charmonium production in $e^+e^-$ annihilation at $\sqrt{s}=10.6GeV$. NRQCD predictions for the $J/ψ$ production are compared with the recent measurements by BaBar and Belle. A NRQCD calculation for the $D$-wave charmonium production is reported to further test the color-octet mechanism and detect the $J^{PC}=2^{--}$ state. The issue of double $c \bar c$ production in $e^+e^-$ annihilation observed by Belle is also discussed.

hep-ph↗
arXiv2002

$B \to π^+ π^-, K π, K \etap$ decays and new physics effects in the general two-Higgs-doublet model: an update

In this paper, we reexamine the new physics contributions to seven well measured $B \to PP$ decays in the standard model (SM) and the general two-Higgs-doublet model (model III) and compare the theoretical predictions with the new data. Within the considered parameter space we found that: (a) the measurements of the branching ratios for $B\to π^+ π^-, K^- π^+$ and $K^0 π^+$ lead to a strong constraint on the form factor $F_0^{Bπ}(0)$: $F_0^{Bπ}(0)=0.24 \pm 0.03$; (b) the new physics enhancements to the penguin-dominated $B \to K π$ and $K \etap$ decays are significant in size, $\sim (40-65)%$ $w.r.t$ the SM predictions, and play an important role in restoring the consistency between the data and the theory.

hep-ph↗
arXiv2002

$\etap K$ puzzle of B meson decays and new physics effects in the general two-Higgs-doublet model

we calculate the new physics contributions to seven measured decays $B \to π^+ π^-, K π$ and $ K \etap$ in the general two-Higgs-doublet model (Model III). Within the considered parameter space, we find that: (a) the CLEO/BaBar measurement of $B\to π^+ π^-$ decay prefers a small $F_0^{Bπ}(0)$: $F_0^{Bπ}(0)=0.25 \pm 0.03$; (b) the new physics enhancements to the penguin-dominated $B \to Kπ$ and $B\to K \etap$ decays are significant in size, $\sim (40-70)%$ $w.r.t$ the standard model predictions; and (c) the new physics enhancements can boost the branching ratios ${\cal B}(B \to K^+ \etap)$ and ${\cal B}(B \to K^0 \etap)$ to be consistent with the data within one standard deviation, and hence lead to a simple and plausible new physics interpretation for the $\etap K$ puzzle.

hep-ph↗
arXiv2002

Diffractive D_s production in charged current DIS

We present a perturbative QCD calculation of diffractive $D_s$ production in charged current deep inelastic scattering. In the two-gluon exchange model, we analyze the diffractive process $νN \to μ^- N \Ds$, which may provide useful information for the gluon structure of nucleons and the diffraction mechanism in QCD. The cross section of diffractive $D_s$ production with $\xBj=0.005$-0.05 and $E_ν=50$ Gev is found to be $2.7\times10^{-5}$ pb. In spite of this small cross section, the high luminosity available at the $ν$-Factory in the future would lead to a sizable number of diffraction events.

hep-ph↗
arXiv2001

Polarizations of J/ψand ψ' in hadroproduction at Tevatron in the k_t factorization approach

We present a calculation for the polarizations of $J/ψ$ and $ψ'$ produced in the hadron collisions at the Fermilab Tevatron. Various color octet channels including ${}^1S_0^{(8)}$, ${}^3P_J^{(8)}$, and ${}^3S_1^{(8)}$ as well as contributions from $χ_{cJ}$ decays are considered in the $k_t$ factorization approach. We find that in a rather wide range of the transverse momenta of $J/ψ$ and $ψ'$, the production rates could be dominated by the ${}^1S_0^{(8)}$ channel, and the predicted polarizations from the ${}^1S_0^{(8)}$ channel and $χ_{cJ}$ feeddown contributions are roughly compatible with the preliminary CDF data. This might provide a possible release from the conflict between the NRQCD collinear parton model calculations and the CDF data.

hep-ph↗
arXiv2000

χ_{cJ} polarizations at the Fermilab Tevatron

We propose the measurement of $χ_{cJ}$ polarizations at high energy hadron colliders to study heavy quarkonium production mechanism. We find that the color-singlet model in the $k_t$ factorization approach predicts very different behavior for $χ_{cJ}$ polarizations at the Fermilab Tevatron compared with the NRQCD predictions in the collinear parton model. In the color-singlet $k_t$ factorization approach, for both $χ_{c1}$ and $χ_{c2}$ productions, the helicity $h=0$ states dominate over other helicity states at large $p_T$. These properties are very useful in distinguishing between the two production mechanisms which are related to the interesting issue of $Jψ$ and $ψ'$ polarizations, and may provide a crucial test for the $k_t$ factorization approach.

hep-ph↗
arXiv2000

Charmless hadronic decays $B \to PP, PV, VV$ and new physics effects in the general two-Higgs doublet models

Based on the low-energy effective Hamiltonian with the generalized factorization, we calculate the new physics contributions to the branching ratios of the two-body charmless hadronic decays of $B_u$ and $B_d$ mesons induced by the new gluonic and electroweak charged-Higgs penguin diagrams in the general two-Higgs doublet models (models I, II and III). Within the considered parameter space, we find that: (a) the new physics effects from new gluonic penguin diagrams strongly dominate over those from the new $γ$- and $Z^0$- penguin diagrams; (b) in models I and II, new physics contributions to most studied B meson decay channels are rather small in size: from -15% to 20%; (c) in model III, however, the new physics enhancements to the penguin-dominated decay modes can be significant, $\sim (30 -200)%$, and therefore are measurable in forthcoming high precision B experiments; (d) the new physics enhancements to ratios ${\cal B}(B \to K \etap)$ are significant in model III, $\sim (35 -70)%$, and hence provide a simple and plausible new physics interpretation for the observed unexpectedly large $B \to K \etap $ decay rates; (e) the theoretical predictions for ${\cal B}(B \to K^+ π)$ and ${\cal B}(B \to K^0 π^+)$ in model III are still consistent with the data within $2σ$ errors; (f) the significant new physics enhancements to the branching ratios of $B \to K^0 π^0, K^* η, K^{*+} π^-, K^+ ϕ, K^{*0} ω, K^{*+} ϕ$ and $K^{*0} ϕ$ decays are helpful to improve the agreement between the data and the theoretical predictions; (g) the theoretical predictions of ${\cal B}(B \to PP, PV, VV)$ in the 2HDM's are generally consistent with experimental measurements and upper limits ($90% C.L.$)

hep-ph↗
arXiv2000

Inelastic electroproduction of $η_c$ at ep colliders

Using the nonrelativistic QCD factorization formalism, we calculate the electroproduction cross sections of $η_c$ in ep collisions, including the contribution from both the transverse photon and the longitudinal photon. For this process the color-singlet contribution vanishes up to the next to leading order perturbative QCD calculations. The dominant contribution comes from the color-octet ${}^1S_0^{(8)}$ subprocess. The nonperturbative color-octet matrix element of ${}^1S_0^{(8)}$ of $η_c$ is related to that of ${}^3S_1^{(8)}$ of $J/ψ$ by heavy quark spin symmetry, and the latter can be determined from the direct production of $J/ψ$ at large transverse momentum at the Fermilab Tevatron. The measurement of this process at DESY HERA can be viewed as another independent test for the color-octet production mechanism

hep-ph↗
arXiv2000

Charm multiplicity and the branching ratios of inclusive charmless b quark decays in the general two-Higgs-doublet models

In the framework of general two-Higgs-doublet models, we calculate the branching ratios of various inclusive charmless b decays by using the low energy effective Hamiltonian including next-to-leading order QCD corrections, and examine the current status and the new physics effects on the determination of the charm multiplicity $n_c$ and semileptonic branching ratio $B_{SL}$. Within the considered parameter space, the enhancement to the ratio $BR(b \to s g)$ due to the charged-Higgs penguins can be as large as a factor of 8 (3) in the model III (II), while the ratio $BR(b \to no charm)$ can be increased from the standard model prediction of 2.49% to 4.91% (2.99%) in the model III (II). Consequently, the value of $B_{SL}$ and $n_c$ can be decreased simultaneously in the model III. The central value of $B_{SL}$ will be lowered slightly by about 0.003, but the ratio $n_c$ can be reduced significantly from the theoretical prediction of $n_c= 1.28 \pm 0.05$ in the SM to $n_c= 1.23 \pm 0.05$, $1.18 \pm 0.05$ for $m_{H^+}=200, 100$ GeV, respectively. We find that the predicted $n_c$ and the measured $n_c$ now agree within roughly one standard deviation after taking into account the effects of gluonic charged Higgs penguins in the model III with a relatively light charged Higgs boson.

hep-ph↗
arXiv1999

Gluon penguin enhancements to inclusive charmless decays of b quark in the 2HDM with flavor changing couplings

We calculate the enhancements to the inclusive charmless decays of b quark, $b \to s g, s q\bar{q}, sgg$, from gluon penguin diagrams induced by the charged and neutral Higgs bosons $(H^{\pm}, h^0, H^0$, and A^0) in the Two-Higgs-Doublet Model with flavor-changing couplings. Within the considered parameter space, the new contributions from charged Higgs boson are dominant. After including the new contributions, the branching ratio $BR(b \to sg)$ (q^2 =0) can be increased form $\sim 0.2%$ in the standard model to 4.4% and 2.6% in the two-Higgs-doublet model for $m_{H^+}=100$ and 200 GeV, respectively. The new contribution to the decay mode $b \to s q \bar{q}$ with q=(u,d,s) is, however, numerically small and peaked at the lower q^2 region. The new contribution to $b \to s gg$ can also be neglected.

hep-ph↗
arXiv1999

Inelastic $J/ψ$ production in polarized photon-hadron collisions

Presented here is a calculation of inelastic $J/ψ$ production in polarized photon-hadron collisions under the framework of NRQCD factorization formalism. We consider the photoproduction of $\jpsi$ in the energy range relevant to HERA. The Weizsäcker-Williams approximation is adopted in the evaluation of the cross sections for $ep$ collisions. We found that this process can give another independent test for the color-octet mechanism, and the different features for the two color-octet processes may provide further informations on the mechanism for inelastic $\jpsi$ photoproduction. And the discrepancy on the production asymmetry $A$ between various sets of polarized gluon distribution functions is also found to be distinctive.

hep-ph↗
arXiv1999

Diffractive charm jet production at hadron colliders in the two-gluon exchange model

We present a calculation of diffractive charm jet production at hadron colliders in perturbative QCD based on the two-gluon exchange model. Differing from the previous calculations, we abandon the use of the effective color-singlet vitual gluon simplification, and use the real gluon in the calculations for the partonic process. We find the final result is free of the linear singularities due to the small transverse momenta of the exchanged two gluons. In the leading logarithmic approximation (LLA) in QCD, this process is related to the off-diagonal gluon density in the proton. As a result, this process may provide a wide window for testing the two-gluon exchange model, and may be particularly useful in studying the small $x$ physics. In comparison, the diffractive bottom jet production is also discussed, and is found to be important only for large transverse momentum of the jet.

hep-ph↗
arXiv1999

Quark initiated coherent diffractive production of muon pair and W boson at hadron colliders

The large transverse momentum muon pair and W boson productions in the quark initiated coherent diffractive processes at hadron colliders are discussed under the framework of the two-gluon exchange parametrization of the Pomeron model. In this approach, the production cross sections are related to the small-x off-diagonal gluon distribution and the large-x quark distribution in the proton (antiproton). By approximating the off-diagonal gluon distribution by the usual gluon distribution function, we estimate the production rates of these processes at the Fermilab Tevatron.

hep-ph↗
arXiv1999

Diffractive light quark jet and gluon jet production at hadron colliders in the two-gluon exchange model

Massless diquark jet and gluon jet productions at large transverse momentum in the coherent diffractive processes at hadron colliders are studied in the two-gluon exchange parametrization of the Pomeron model. We use the helicity amplitude method to calculate the cross section formulas. We find that for the light quark jet and gluon jet production the diffractive process is related to t he differential off-diagonal gluon distribution function in the proton. We estimate the production rate for these processes at the Fermilab Tevatron by approximating the off-diagonal gluon distribution function by the usual diagonal gluon distribution in the proton. We also use the helicity amplitude method to calculate the diffractive charm jet production at hadron colliders, by which we reproduce the leading logarithmic approximation result of this process we previously calculated.

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