arXiv subjects

Feng Yuan

Publications and source records attributed to Feng Yuan.

422 records · Page 24Linked to original sources

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

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

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↗