arXiv subjects

Kuang-Ta Chao

Publications and source records attributed to Kuang-Ta Chao.

At least 109 records · Page 6Linked to original sources

arXiv1999

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

Massless quark and antiquark jet production at large transverse momentum in the coherent diffractive processes at hadron colliders is calculated in the two-gluon exchange parametrization of the Pomeron model. We use the helicity amplitude method to calculate the cross section formula. We find that for the light quark jet production the diffractive process is related to the differential off-diagonal gluon distribution function in the proton. We estimate the production rate for this process at the Fermilab Tevatron by approximating the off-diagonal gluon distribution function by the usual diagonal gluon distribution in the proton. And we find that the cross sections for the diffractive light quark jet production and the charm quark jet production are in the same order of magnitude. 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.

hep-ph↗

arXiv1999

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

Following our recent paper on the calculations of diffractive quark jet production at hadron colliders, we present here the calculations of gluon jet production at hadron colliders in the two-gluon exchange parameterization of the Pomeron model. We use the helicity amplitude method to calculate the cross section formula. We find that for the gluon jet production the diffractive process is related to the differential off-diagonal gluon distribution function in the proton. We estimate the production rate for this process at the Fermilab Tevatron by approximating the off-diagonal gluon distribution function by the usual diagonal gluon distribution.

hep-ph↗

arXiv1999

Large transverse momentum direct photon production in the coherent diffractive processes at hadron colliders

Direct photon production at large transverse momentum in the coherent diffractive processes at hadron colliders is calculated in the two-gluon exchange model. We find that the amplitude for the production process is related to the differential off-diagonal gluon distribution function in the proton. We estimate the production rate at the Fermilab Tevatron by approximately using the usual gluon distribution function. Because of the clean signature, this process can be used to detailed study the small-x physics, and the coherent diffractive processes at hadron colliders.

hep-ph↗

arXiv1999

Photoproduction of $η_c$ in NRQCD

We present a calculation for the photoproduction of $η_c$ under the framework of NRQCD factorization formalism. We find a quite unique feature that the color-singlet contribution to this process vanishes at not only the leading order but also the next to leading order perturbative QCD calculations and that 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 the heavy quark spin symmetry, and the latter can be determined from the direct production of $J/ψ$ at large transverse momentum at the Fermilib Tevatron. We then conclude that the measurement of this process may clarify the existing conflict between the color-octet prediction and the experimental result on the $J/ψ$ photoprodution.

hep-ph↗

arXiv1998

D-wave heavy quarkonium production in fixed target experiments

We calculate the $D$-wave heavy quarkonium production at fixed target experiments under the NRQCD factorization formalism. We find that the color octet contributions are two orders of magnitude larger than color-singlet contributions if color-octet matrix elements are taken according to the NRQCD velocity scaling rules. Within the theoretical uncertainties, the prediction for the production rate of $2^{--}$ $D$-wave charmonium state agrees with the preliminary result of E705 and other experiments. Searching for the $1^{--}$ $D$-wave state $ψ(3770)$ is further suggested.

hep-ph↗

arXiv1998

Diffractive $\jpsi$ production through Color-Octet mechanism at hadron colliders

We propose the color-octet mechanism combined with the two gluon exchange model for the diffractive $J/ψ$ production in hadron collisions. In the leading logarithmic approximation (LLA) in QCD, we find that the diffractive $J/ψ$ production rate is related to the off-diagonal gluon density in the proton and to the nonperturbative color-octet matrix element of $J/ψ$. The rate is found to be very sensitive to the gluon density at very small values of $x$ (down to $x=O(10^{-6})$). 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. And it may also be a golden place to test the color-octet mechanism proposed by solving the $ψ'(J/ψ)$ surplus problem at the Tevatron.

hep-ph↗

arXiv1998

Quarkonium production in SM Higgs decays

We investigate the SM Higgs decays into heavy quarkonia J/ψand Υin both color-singlet and color-octet mechanisms. It is found that in J/ψproduction the contribution through color-octet processes overwhelm that in color-singlet processes all the intermediate region M_Z<M_{H^0}<2 M_w and the fraction ratio is comparatively large, but in Υproduction the contribution through color-octet mechanism is negligible.

hep-ph↗

arXiv1998

Gluon fragmentation to $^3D_J$ quarkonium and test of color-octet production mechanism

We report the recent progress in the studies of D-wave heavy quarkonia production from gluon fragmentation at the Tevatron and in Z^0 decays, and the D-wave charmonia production in B decays. We show that the color-octet contributions are of crucial importance to the production of D-wave quarkonia. Signals, as strong as that for J/ψand ψ^\prime, should be seen for the D-wave charmonium in the processes. These will provide a test of the color-octet production mechanism.

hep-ph↗

arXiv1998

Diffractive J/psi production as a probe of the gluon component in the Pomeron

Presented here is a study of the large p_T J/psi production in hard diffractive process by the pomeron exchange at the Fermilab Tevatron. We find that this process (p\bar p \to p+J/psi+X) can be used to probe the gluon content of the pomeron and to measure the gluon fraction of the pomeron. And the diffractive direct J/psi production can also provide another crucial test for the color-octet fragmentation mechanism. Using the renormalised pomeron flux factor D\approx 1/9, the single diffractive J/psi production cross section at large p_T (\geq 8GeV) is found to be of order of 0.01 nb, and the ratio of the single diffractive to the non-diffractive J/psi production is 0.65\pm 0.15% for the gluon fraction f_g=0.7\pm 0.2.

hep-ph↗

arXiv1997

Color-singlet and color-octet J/psi production in top quark rare decays

J/psi production in top quark rare decays is investigated under the framework of NRQCD factorization formalism. Various production channels are studied, and we find that the contributions from the color-singlet quark fragmentation and the color-octet gluon fragmentation are both over 3 orders larger than that from the leading order color-singlet process. The numerical results show that the branching ratio B(t -> c + J/psi + X) is about 10^{-14} in the SM, and 10^{-10} in the MSSM.

hep-ph↗

arXiv1997

QCD Radiative Correction to the Hadronic Annihilation Rate of $1^{+-}$ Heavy Quarkonium

Hadronic annihilation rate of $1^{+-}$ heavy quarkonium is given to next-to-leading order in $α_s$ and leading order in $v^2$ using a recently developed factorization formalism which is based on NRQCD. The result includes both the annihilation of P-wave color-singlet $Q\bar{Q}$ component, and the annihilation of S-wave color-octet $Q\bar{Q}$ component of the quarkonium. The notorious infrared divergences due to soft gluons, i.e., the Logarithms associated with the binding energy, encountered in previous perturbative calculations of $1^{+-}$ quarkonium decays are found to be explicitly cancelled, and a finite result for the decay width to order $α_s^3$ is then obtained.

hep-ph↗

arXiv1997

High-$p_T$ $ψψ$ production as signals for Double Parton scattering at hadron colliders

We present an analysis of the ψψproduction from double parton (DP) sacttering and single parton (SP) scattering in the large p_T region via color-octet gluon fragmentation. We find that at the Tevatron the DP ψψproduction is at the edge of the detectability at present, and at the LHC the DP cross section will dominate over the SP cross section in the lower p_T(min) region (i.e., p_T(min)<7GeV). We also conclude that the color-octet mechanism is of crucial importance to the double j/psi production at high energy hadron colliders.

hep-ph↗

arXiv1997

The Color-Octet intrinsic charm in $η^\prime$ and $B\to η^\prime X$ decays

Color-octet mechanism for the decay B\to η^\prime X is proposed to explain the large branching ratio of Br(B\to η^\prime X)\sim 1\times 10^{-3} recently announced by CLEO. We argue that the inclusive η^\prime production in B decays may dominantly come from the Cabbibo favored b\to (\bar c c)_8s process where \bar c c pair is in a color-octet configuration, and followed by the nonperturbative transition (\bar c c)_8\to η^\prime X. The color-octet intrinsic charm component in the higher Fock states of η^\prime is crucial and is induced by the strong coupling of η^\prime to gluons via QCD axial anomaly.

hep-ph↗

arXiv1997

Determination of color-octet matrix elements from e^+e- process at low energies

We present an analysis of the preliminary experimental data of direct j/psi production in e^e- process at low energies. We find that the color-octet contributions are crucially important to the cross section at this energy region, and their inclusion produces a good description of the data. By fitting to the data, we extract the individual values of two color-octet matrix elements: <{\cal O}_8^ψ(^1S_0)> \approx 1.1\times 10^{-2} GeV^3, <{\cal O}_8^ψ(^3P_0)> m_c^2\approx 7.4\times 10^{-3}GeV^3. We discuss the allowed range of the two matrix elements constrained by the theoretical uncertainties. We find that <{\cal O}_8^ψ(^1S_0)> is poorly determined because it is sensitive to the variation of the choice of m_c, α_s and <{\cal O}_1^ψ(^3S_1)>. However <{\cal O}_8^ψ(^3P_0)> m_c^2 is quite stable (about (6-9)\times 10^{-3}GeV^3) when the parameters vary in reasonable ranges. The uncertainties due to large experimental errors are also discussed.

hep-ph↗

arXiv1997

Prompt J/psi production at e^+e^- colliders

In this paper, we discuss the prompt j/psi production at e^+e^- colliders via color-singlet and color-octet production mechanisms. The color-singlet production processes include 1) e^+e^- to J/ψgg; 2) e^+e^- to J/ψc\bar{c}; 3) e^+e^- to q \bar q ggJ/ψand e^+e^- to q \bar q gχ_c followed by χ_c to J/ψγ. The color-octet production processes include 1) e^+e^- to J/ψg; 2) e^+e^- to j/psi q\bar q. Of all these production channels, we find that the color-octet contributions dominate over the color-singlet contributions at any energy scales. At low energies (\sqrt{s}< 20 GeV), the dominant channel is e^+e^- to J/ψg whereas at high energies e+e^- to j/psi q\bar q will take the leading part. We also find that the energy spectrum for the color-octet j/psi production in process e^+e^- to j/psi q\bar q is very soft, and the mean energy of the produced j/psi is only about 10 GeV~ 20 GeV even at very high energies (e.g. at 1000 GeV). The extraction of color-octet matrix elements from j/psi production in e^+e^- collisions is also discussed.

hep-ph↗

arXiv1997

D-wave charmonium production in B decays

The calculation of D-wave charmonium prodution rates in B meson deacys under the NRQCD factorization formalism is presented. We find that inclusion of the color-octet contributions permits us to detect the D-wave charmonium states in B decays at present experimental facilities. The same amount signals of 2^{--} D-wave state as that of ψ' could be observed at LEP and CESR. We also predict the relative production rates for four D-wave states are δ^c:δ^c_1: δ^c_2:δ^c_3=2.5:3:5:7, where δ^c, δ^c_1, δ^c_2, δ^c_3 represent respectively the 2^{-+}, 1^{--}, 2^{--}, 3^{--} states.

hep-ph↗

arXiv1997

Gluon fragmentation to ^3D_J quarkonia

We present a calculation of the leading order QCD fragmentation functions for gluons to split into spin-triplet D-wave quarkonia. We apply them to evaluate the gluon fragmentation contributions to inclusive ^3D_J quarkonium production at large transverse momentum processes like the Tevatron and find that the D-wave quarkonia, especially the charmonium 2^{--} state, could be observed through color-octet mechanism with present luminosity. Since there are distinctively large gaps between the contributions of two different (i.e, color-singlet and color-octet) quarkonium production mechanisms, our results may stand as a unique test to NRQCD color-octet quarkonium production mechanism.

hep-ph↗

arXiv1996

QCD predictions for annihilation decays of P-wave quarkonia to next-to-leading order in $α_s$

The decay rates of P-wave heavy quarkonia to light hadrons are presented to leading order in $v^2$ and next-to-leading order in $α_s$. They include contributions from both the color-singlet component and the color-octet component of quarkonia. Applying these results to charmonium and using measured decay rates for the $χ_{c1}$ and $χ_{c2}$ by E760, we determine the two nonperturbative decay matrix elements, and then predict the hadronic decay rates of $χ_{c0}$ and $h_c$, and the electromagnetic decay rates of $χ_{c0}$ and $χ_{c2}$. The obtained decay rates of $χ_{c0}\to LH$ and $χ_{c0}\toγγ$ are in agreement with the Crystal Ball result, and also with the new measurement by BES. However, the results for $Γ(χ_{c0}\to LH)$ are dependent on the choice of renormalization scale.

hep-ph↗