arXiv subjects

Kuang-Ta Chao

Publications and source records attributed to Kuang-Ta Chao.

117 records · Page 7Linked to original sources

arXiv1996

Cancellation of Infrared Divergences in Hadronic Annihilation Decays of Heavy Quarkonia

In the framework of a newly developed factorization formalism which is based on NRQCD, explicit cancellations are shown for the infrared divergences that appeared in the previously calculated hadronic annihilation decay rates of P-wave and D-wave heavy quarkonia. We extend them to a more general case that to leading order in $v^2$ and next-to-leading order in $α_s$, the infrared divergences in the annihilation amplitudes of color-singlet $Q\bar{Q}(^{2S+1}L_J)$ pair can be removed by including the contributions of color-octet operators $Q\bar{Q}(^{2S+1}(L-1)_{J'})$, $Q\bar{Q}(^{2S+1}(L-3)_{J''})$, ... in NRQCD. We also give the decay widths of $^3D_J\rightarrow LH$ at leading order in $α_s$.

hep-ph↗

arXiv1996

Physics in Charm Energy Region

Recent results on physics in the charm energy region are reviewed. (1) The new data and puzzles in exclusive hadronic decays of $J/ψ$ and $ψ'$ give new challenges to the theory of hadronic decays. (2) With the new observation for $ξ(2230)$ and $f_0(1500)$ in $J/ψ$ radiative decays and other experiments, the situation in searching for glueballs is encouraging, but theoretical uncertainties related to the properties of glueballs still remain and need to be further reduced. (3) For the prompt production of charmonium at large transverse momentum, gluon and quark fragmentations dominate over leading-order parton fusions. Color-singlet fragmentation is not the dominant mechanism for $J/ψ$ and $ψ'$ production. Color-octet fragmentation seems to be important to explain the $J/ψ$ and, in particular, the $ψ'$ excess, but further tests are required. The mechanism of charmonium production at fixed-target also needs studying. (4) Some theoretical and experimental results in charmonium and open charm hadrons are also reported.

hep-ph↗

arXiv1996

A Crucial Test for Color-Octet Production Mechanism in Z^0 Decays

The direct production rates of $D$-wave charmonia in the decays of $Z^0$ is evaluated. The color-octet production processes $Z^0\rightarrow ^3D_J(c\bar c) q\bar q$ are shown to have distinctively large branching ratios, the same order of magnitude as that of $J/ψ$ prodution, as compared with other $D$-wave charmonium production mechanisms. This may suggest a crucial channel to test the color-octet mechanism as well as to observe the $D$-wave charmonium states in $Z^0$ decays. In addition, a signal for the $^3D_J$ charmonium as strong as $J/ψ$ or $ψ^\prime$ with large transverse momentum at the Tevatron should also be observed.

hep-ph↗

arXiv1996

Color-Octet Charmonium Production in Top Quark Decays

We calculate the direct production rate of $J/ψ$ in top quark decays. The color-octet $J/ψ$ production via $t\rightarrow W^+ b J/ψ$ is shown to have a large branching ratio of order $1.5\times 10^{-4}$, which is over an order of magnitude higher than that of the color-singlet $J/ψ$ production via $t\rightarrow W^+ b J/ψ~g~g $ or $t\rightarrow W^+ b~χ_{cJ}~g$ followed by $χ_{cJ}\rightarrow J/ψ~γ$. This result can be used as a powerful tool to test the importance of the color-octet mechanism in heavy quarkonium production.

hep-ph↗

arXiv1996

Possible retardation effects of quark confinement on the meson spectrum

The reduced Bethe-Salpeter equation with scalar confinement and vector gluon exchange is applied to quark-antiquark bound states. The so called intrinsic flaw of Salpeter equation with static scalar confinement is investigated. The notorious problem of narrow level spacings is found to be remedied by taking into consideration the retardation effect of scalar confinement. Good fit for the mass spectrum of both heavy and light quarkomium states is then obtained.

hep-ph↗

arXiv1996

Top Quark Decays into Heavy Quark Mesons

For top quark decays into heavy quark mesons $Υ$ and $\bar{B}_c^*$ , a complete calculation to the leading order both in QCD coupling constant $α_s$ and in $v$, the typical velocity of the heavy quarks inside the mesons, is performed. Relatons between the top quark mass and the decay branching ratios are studied. Comparion with the results which are obtained by using the quark frangmentation functions is also discussed. The branching ratios are consistent (within a factor of $2\sim 3 $) with that obtained using fragmentation functions at $m_t\sim 150$ GeV.

hep-ph↗

arXiv1996

Electromagnetic Annihilation Rates of $χ_{c0}$ and $χ_{c2}$ with Both Relativistic and QCD Radiative Corrections

We estimate the electromagnetic decay rates of $χ_{c0}\rightarrow γγ$ and $χ_{c2}\rightarrowγγ$ by taking into account both relativistic and QCD radiative corrections. The decay rates are derived in the Bethe-Salpeter formalism and the QCD radiative corrections are included in accordance with factorization assumption. Using a QCD-inspired interquark potential, we obtain relativistic BS wavefunctions of $χ_{c0}$ and $χ_{c2}$ by solving BS equations for the corresponding $^{2S+1}L_J$ states. Our numerical result for the ratio $R=\frac{Γ(χ_{c0}\rightarrowγγ)}{Γ(χ_{c2} \rightarrowγγ)}$ is about $11-13$ which agrees with the update E760 experimental data. Explicit calculations show that the relativistic corrections due to spin-dependent interquark forces induced by gluon exchange enhance the ratio $R$ substantially and its value is insensitive to the choice of parameters that characterize the interquark potential. Our expressions for the decay widths are identical with that obtained in the NRQCD theory to the next-to-leading order in $v^2$ and $α_s$. Moreover, we have determined two new coefficents in the nonperturbative matrix elements for these decay widths.

hep-ph↗

arXiv1996

Pseuduscalar Heavy Quarkonium Decays With Both Relativistic and QCD Radiative Corrections

We estimate the decay rates of $η_c\rightarrow 2γ$, $η_c'\rightarrow 2γ$, and $J/ψ\rightarrow e^+ e^-$, $ψ^\prime\rightarrow e^+e^-$, by taking into account both relativistic and QCD radiative corrections. The decay amplitudes are derived in the Bethe-Salpeter formalism. The Bethe-Salpeter equation with a QCD-inspired interquark potential are used to calculate the wave functions and decay widths for these $c\bar{c}$ states. We find that the relativistic correction to the ratio $R\equiv Γ(η_c \rightarrow 2γ)/ Γ(J/ ψ\rightarrow e^+ e^-)$ is negative and tends to compensate the positive contribution from the QCD radiative correction. Our estimate gives $Γ(η_c \rightarrow 2γ)=(6-7) ~keV$ and $Γ(η_c^\prime \rightarrow 2γ)=2 ~keV$, which are smaller than their nonrelativistic values. The hadronic widths $Γ(η_c \rightarrow 2g)=(17-23) ~MeV$ and $Γ(η_c^\prime \rightarrow 2g)=(5-7)~MeV$ are then indicated accordingly to the first order QCD radiative correction, if $α_s(m_c)=0.26-0.29$. The decay widths for $b\bar b$ states are also estimated. We show that when making the assmption that the quarks are on their mass shells our expressions for the decay widths will become identical with that in the NRQCD theory to the next to leading order of $v^2$ and $α_s$.

hep-ph↗

arXiv1995

Glueball Interpretation of $ξ$(2230)

On the basis of the results of $ξ(2230)\rightarrowπ^{+}π^{-}, p\bar{p}$ and $K\bar{K}$, measured by the BES Collaboration in radiative J/$ψ$ decays, combined with the upper limit of Br($ξ\rightarrow p\bar{p}$)Br($ξ\rightarrow K\bar{K}$), measured by PS185 experiment, we argue that the distinctive properties of $ξ$(2230), the flavor-symmetric decays and the narrow partial decay widths to $ππ$ and $K\bar{K}$ as well as its copious production in radiative J/$ψ$ decay, would strongly favor the glueball interpretation of $ξ$(2230).

hep-ph↗