arXiv subjects
Publications and source records attributed to Qiang Zhao.
We discuss the scalar meson mixing scenario and present an OZI rule violation mechanism for understanding the scalar productions in charmoium hadronic decays. We stress that the OZI violation could play a key role in disentangling the structure of the scalars: $f_0(1370)$, $f_0(1500)$ and $f_0(1710)$.
The electromagnetic decay contributions to $J/ψ(ψ^\prime)\to VP$, where $V$ and $P$ stand for vector and pseudoscalar meson, respectively, are investigated in a vector meson dominance (VMD) model. We show that $J/ψ(ψ^\prime)\to γ^*\to VP$ can be constrained well with the available experimental information. We find that this process has significant contributions in $ψ^\prime\to VP$ and may play a key role in understanding the deviations from the so-called "12% rule" for the branching ratio fractions between $ψ^\prime\to VP$ and $J/ψ\to VP$. We also address that the "12% rule" becomes very empirical in exclusive hadronic decay channels.
We investigate the possibility of producing the enhancement observed in $J/ψ\to γX$ with $X\to ωϕ$ at BES by intermediate meson rescatterings through $f_0(1710)\to PP\to ωϕ$, $f_0(1710)\to VV\to ωϕ$, and $f_0(1710)\to SS\to ωϕ$. We find that intermediate meson rescatterings can produce some enhancement near the $ωϕ$ threshold. Implications about the property of this enhancement are discussed.
We identify a "$Λ$ selection rule" for $N^*$ resonances in the presence of QCD mixing effects. We quantify these mixing effects from existing data and predict amplitudes for exciting {\bf 20} representations in SU(6), which are forbidden in strict diquark models. By classifying Particle-Data-Group (PDG) states at N=2, we show that $γN\to KΛ$, $K^*Λ$, $KΣ$, $K^*Σ$, and $J/ψ\to \bar{p}N^*$ are ideal probes of baryon dynamics and for establishing whether strongly correlated diquarks survive for $L > 0$.
We discuss the Okubo-Zweig-Iizuka (OZI) rule violation effects in $η_c\to VV$ in light of the new data from BES Collaboration. In particular, a possible non-vanishing branching ratio for $η_c\to ωϕ$ provides a hint of the degrees of OZI violations based on a recent factorization proposed for charmonium hadronic decays. The violation mechanism is studied via an intermediate meson exchange model. The results are consistent with the experimental observations.
We investigate the correlations between the scalar meson configurations and Okuba-Zweig-Iizuka (OZI) rule violations in the hadronic decays of heavy quarkonia, e.g. $J/ψ$ and $Υ$, into isoscalar vector meson ($ϕ$ and $ω$) and scalar mesons ($f_0(1710)$, $f_0(1500)$, and $f_0(1370)$). It shows that the dramatic change of the values of the branching ratio fraction of $ϕf_0/ωf_0$ from low (e.g. in $J/ψ$ decays) to high energies (e.g. in $Υ$ decays) will not only test the glueball-$Q\bar{Q}$ mixings, but also provide important information about the mysterious OZI-rule violations within the scalars.
We investigate the decays of $χ_{c0,2}$ into vector meson pairs ($VV$), pseudoscalar pairs ($PP$), and scalar pairs ($SS$) in a general factorization scheme. The purpose is to clarify the role played by the OZI-rule violations and SU(3) flavour breakings in the decay transitions, and their correlations with the final state meson wavefunctions. For $χ_{c0,2}\to VV$ and $PP$, we obtain an overall self-contained description of the experimental data. Applying this factorization to $χ_{c0}\to f_0^i f_0^j$, where $i, j=1, 2, 3$ denotes $f_0(1710)$, $f_0(1500)$ and $f_0(1370)$, respectively, we find that specific patterns will arise from the model predictions for the decay branching ratio magnitudes, and useful information about the structure of those three scalars can be abstracted.
A coherent study of the production of $f_0^i$ ($i=1$, 2, 3 corresponding to $f_0(1710)$, $f_0(1500)$, and $f_0(1370)$) in $J/ψ\to V f_0 \to V PP$ is reported based on a previously proposed glueball and $Q\bar{Q}$ nonet mixing scheme, and a factorization for the decay of $J/ψ\to V f_0^i$, where $V$ denotes the isoscalar vector mesons $ϕ$ and $ω$, and $P$ denotes pseudoscalar mesons. The results show that the $J/ψ$ decays are very sensitive to the structure of those scalar mesons, and suggest a glueball in the $1.5-1.7$ GeV region, in line with Lattice QCD. The presence of significant glueball mixings in the scalar wavefunctions produces peculiar patterns in the branching ratios for $J/ψ\to V f_0^i\to VPP$, which are in good agreement with the recently published experimental data from the BES collaboration.
We provide an analysis of vector meson photoproduction in the channel of the vector meson decaying into a pseudoscalar meson plus a photon, i.e. $V\to Pγ$. It is shown that non-trivial kinematic correlations arise from the measurement of the $Pγ$ angular distributions in the overall c.m. system in comparison with those in the vector-meson-rest frame. In terms of the vector meson density matrix elements, the implication of such kinematic correlations in the measurement of polarization observables is discussed. For the $ω$ meson production, due to its relatively large branching ratios for $ω\toπ^0γ$, additional events from this channel may enrich the information about the reaction mechanism and improve the statistics of the recent measurement of polarized beam asymmetries by the GRAAL Collaboration. For $ϕ\to ηγ$, $ρ\to πγ$, and $K^*\to Kγ$, we expect that additional information about the spin structure of the vector meson production vertex can be derived.
We present an analysis of a Beam-Target double polarization asymmetry in $γn\to Θ^+ K^-$. We show that this quantity can serve as a filter for the determination of the $Θ^+$'s spin-parity assignment near threshold. It is highly selective between $1/2^+$ and $1/2^-$ configurations due to dynamical reasons.
A systematic lowering in mass of strangeness ambiguous $pK^0_S$ peaks relative to the $nK^+$ is noted. We discuss how measurement of $γp\to Θ^+ K^0_S\to p K^0_S K^0_S \to pπ^+π^-π^+π^-$ in association with $γp\to Θ^+ K^0_S\to n K^+ K^0_S$ can help to clarify the nature of the narrow baryon state claimed in $p K^0_S$ invariant mass distributions. This can both establish the $Θ^+$ in a single experiment and also reveal, or place severe limits on, the existence of an associated $Σ_5$ pentaquark.
We show how deviations from the dimensional scaling laws for exclusive processes may be related to a breakdown in the locality of quark-hadron duality, i.e. the "restricted locality". For exclusive reactions like meson photo- and electroproduction above the resonance region, we explore the effects arising from such a local duality breaking and propose that it can be a possible source for oscillations about the smooth quark counting rule predicted by pQCD in the 90-degree differential cross sections.
We present constraints on the {\it relative} photoproduction cross sections of positive parity pentaquark states, $Σ_5$, $Λ_5$, and $N_5$, based on a minimum phenomenology gained in $γN \to K Θ^+$ and their baryon-meson couplings as in the work of Close and Dudek. The possibility of anomalous signals in $γp \to K^0_S (Θ^+;Σ_d^+)$ is discussed. We emphasise the importance of comparing $γN \to K Θ^+$ with "conventional" states such as $γN \to K Σ(1660)$.
We carry out an analysis of the pentaquark $Θ^+$ photoproduction with polarized photon beams. Kinematical and dynamical aspects are examined for the purpose of determining $Θ^+$'s spin and parity. It shows that the polarized photon beam asymmetry in association with certain dynamical properties of the production mechanism would provide further information on its quantum numbers. Facilities at SPring-8, JLab, ELSA, and ESRF will have access to them.
Building on recent work by Brodsky {\it et al.}, we advocate searching for glueball degrees of freedom in $e^+e^- \to J/ψ\to ϕf_0$ at CLEO-c and BES.
We show how deviations from the dimensional scaling laws for exclusive processes may be related to a breakdown in the locality of quark-hadron duality. The essential principles are illustrated in a pedagogic model of a composite system with two spinless charged constituents, for which a dual picture for the low-energy resonance phenomena and high-energy scaling behavior can be established. We introduce the concept of "restricted locality" of quark-hadron duality and show how this results in deviations from the pQCD quark counting rules above the resonance region. In particular it can be a possible source for oscillations about the smooth quark counting rule, as seen e.g. in the 90-degree differential cross sections for $γp\to π^+ n$.
We discuss recent claims that $p\bar{p} \to γγ$ may be described by a generalized parton picture. We propose that quark-hadron duality provides a justification for the effective dominance of the "handbag" diagram assumed in recent literature, and that handbag diagrams may dominate phenomena in kinematic regions far more extensive than that might be expected from pQCD alone.
We show how quark-hadron duality can emerge for valence spin averaged structure functions, and for the non-forward distributions of Deeply Virtual Compton Scattering. Novel factorisations of the non-forward amplitudes are proposed. Some implications for large angle scattering and deviations from the quark counting rules are illustrated.