OZI Rule Research Articles

Search for exotic baryons with hidden strangeness in diffractive production processes

Experimental results of the SPHINX Collaboration on studying proton diffractive production processes are presented. Evidences for new baryon states with masses ≳2 GeV were obtained in hyperon-kaon effective mass spectra in several reactions. Unusual properties of these massive states (small enough decay widths, large branching ratios for their decays with strange particles in final states) make them serious candidates for cryptoexotic pentaquark baryons with hidden strangeness |qqqs s ̄ 〉 . New results for these states are presented here, as well as recent data on large violation of the OZI rule in proton diffractive dissociation.

Loop calculations and OZI rule

The role of two step mechanisms in the OZI rule violation in N N annihilation at low energies is reviewed. The full calculation of two-meson doorway mechanisms shows that the off-mass-shell contributions are important. Moreover, for the Φπ 0 and Φϱ annihilation channels three-meson doorway contributions are non-negligible and improve agreement with the data. A significant enhancement of Φ production is found in the resonant rescattering mechanisms pp → π +π −K K → π +π −Φ and pp → ηK K → ηΦ .

The annihilation process [formula omitted] at rest in liquid and gaseous hydrogen

The preliminary analysis of the reaction pp → π 0ω ( ω → π + π − π 0) at rest, both in liquid and NTP gaseous hydrogen targets, performed with the Obelix apparatus is presented. The values of the measured annihilation frequencies and the study of the angular distributions of the decay products have been used to investigate the initial state distributions of the annihilation and the OZI rule violation.

Hidden strangeness production in two body [formula omitted] annihilation in flight

The relative production rates of the final states Φπ +, ωπ +, ηπ +, η′ π + in np annihilation in flight are studied in order to check OZI rule violation effects in both the vectorial and pseudoscalar sectors.

Study of [formula omitted] and [formula omitted] annihilation reactions in flight

The results of a study of the annihilation reactions np → θπ + and np → ωπ + are reported; the data were collected by the OBELIX apparatus, with antineutrons annihilating in flight (momenta from ∼ 50 MeV/ c to 405 MeV/ c). Annihilation frequencies and annihilation cross sections have been deduced, for both channels, as a function of antineutron momentum. From the cross section ratio, a substantial deviation from OZI rule expectations is observed. An ss quark content in the nucleon offers a fairly plausible explanation for such an effect.

On a deviation of the precise three flavor symmetry of hadrons from SU(3) F

The celebrated SU(3) F symmetry is shown to be inconsistent with the Noether structure of the fundamental electromagnetic current of the udcs-quark quadrupled when considered in the limit of frozen charm degree of freedom. Thus, the SU(3) F is found to be replaced by the heavy c-quark limit of SU(2) ud⊗SU(2) cs⊗U(1). The resulting three-flavor symmetry has the merit of being consistent from the very beginning with the OZI rule, and thereby respects the underlying QCD gluon dynamics. The difference between the two symmetries is revealed by the properties of the non-isotriplet part of the neutral axial current. The latter is probed by the ηN coupling.

Flavour-symmetry correction to the “naı̈ve” Zweig rule for the scalar-meson flavour singlet

We present flavour-symmetric couplings for the OZI-allowed three-meson vertices of effective meson theories, which, for the case of the two-meson channels to which the flavour-singlet scalar meson couples, are endowed with a correction factor with respect to the standard formula.

On loop contributions in the linear sigma model

Quantum loops ares studied in the linear sigma model with scalar and pseudoscalar multiplets and a planar interaction term λ Tr[ΣΣ †ΣΣ †] . It is shown how quantum loops break the OZI rule and the tree-level octet-singlet degeneracy, and how the Goldstone theorem can be maintained also in an iterative scheme including some multiloop diagrams.

Study of φ and f′ 2(1525) meson production in [formula omitted] annihilation at rest

The reaction p ̄ p→K +K −π 0 was analysed for antiproton annihilations at rest at three hydrogen target densities. A strong dependence of the p ̄ p→φπ 0 yield on the quantum numbers of the initial state is observed. The branching ratio of the φπ 0 channel from the 3 S 1 initial state is more than 15 times larger than the one from the 1 P 1 state. A large apparent violation of the OZI rule for tensor meson production from p ̄ p -annihilations from the P-waves (1 +++2 ++) is observed: R exp( f′ 2 π 0/ f 2 π 0)=(149±20)·10 −3, significantly exceeding the OZI-rule prediction R=16·10 −3.

Electromagnetic form factors in theJ/ψmass region: The case in favor of additional resonances

Using the results of our recent analysis of ${e}^{+}{e}^{\ensuremath{-}}$ annihilation, we plot the curves for the diagonal and transition form factors of light hadrons in the timelike region up to the production threshold of an open charm quantum number. The comparison with existing data on the decays of $J/\ensuremath{\psi}$ into such hadrons shows that some new resonance structures may be present in the mass range between 2 GeV and the $J/\ensuremath{\psi}$ mass. Searching them may help in a better understanding of the mass spectrum in both simple and more sophisticated quark models, and in revealing the details of the three-gluon mechanism of the OZI rule breaking in $K\overline{K}$ channel.

The scalar meson nonet and the glueball ground state

New scalar mesons have been discovered in recent experiments. One of these states, the f 0(1500), has unusual properties: a comparatively narrow width and a decay pattern which is incompatible with SU(3) relations based on the OZI rule. The experimental evidence for the new states is discussed. The scalar mesons are arranged into meson nonets; the f 0(1500) is left supernumerous and is interpreted as the ground-state scalar glueball. An alternative interpretation of the scalar meson nonet is also given.

The problem of Okubo–Zweig–Iizuka rule violation in nucleon–antinucleon annihilation at rest

A review of the problem of whether the violation of the OZI rule in nucleon–antinucleon annihilation at rest can be explained in the framework of conventional mechanisms is given in detail. While the vector-dominance model and the rescattering model qualitatively describe the OZI-rule violation in the reactions pp→φγ and pp→φπ 0 for the annihilation from the S state of the protonium atom, the latter model cannot explain the fact that the annihilation into φπ 0 from the P state is not seen and the OZI rule in the reaction pp→f 2 ′ π 0 is not satisfied. We also discuss what information about the OZI-rule violation can be extracted from the reaction pp→φπ + π − and decays of the J/Ψ meson.

Nucleon vector strangeness form factors: multi-pion continuum and the OZI rule

We estimate the 3 \pi continuum contribution to the nucleon strange quark vector current form factors, including the effect of a 3 \pi <----> \rho \pi resonance. We find the magnitude of this OZI-violating contribution to be comparable to that of typical OZI-allowed contributions. We also study the isoscalar electromagnetic form factors, and find that the presence of a \rho \pi resonance in the multi-pion continuum may generate an appreciable contribution.

Study of the OZI selection rule in hadronic processes

In the experiments with LEPTON-F and SPHINX spectrometers the pion-induced charged exchange reactions π- + p → ϕ + n and π- + p → ω + n at Pπ-=32.5 GeV, as well as proton-induced diffractive reactions p + N → [pϕ] + N and p + N → [pω] + N at E p =70 GeV were studied. The comparison of the cross-sections for ϕ and ω-production in these reactions is used for testing the OZI selection rule in hadronic processes. It has been demonstrated that in pion reactions the ratio of the yields of ϕ and ω-mesons R(ϕ/ω) = (3 ± 1) · 10−3 is in a good agreement with naive quark model prediction based on the mixing in vector meson nonet and on the OZI rule (R(ϕ/ω)ozi = tg 2Δθ V − 4 · 10−3). At the same time in proton reactions the effective ratio of ϕ and ω yields is ∼ (4 ÷ 7) · 10-2, i.e. a strong violation of the OZI rule is observed in proton-nucleon interactions. This violation can be in favor of possible existence of some exotic ss̅ component in the quark structure of protons.

OZI rule violations and the strange quark content of the proton

Recent data from p p annihilation at LEAR indicate large violations of the OZI rule for certain final states. The final state dependance together with results on polarized lepton-nucleon scattering led to a model that assumes that there is a polarized s s component in the nucleon wave function. The data and this model will be presented and in the end a little phenomenological model is used to explain part of the strangeness enhancement that is seen in ultra-relativistic heavy ion reactions.

OZI rule violation in p¯p annihilation into φππ by two step processes

The phi pi+ pi- production in p pbar annihilation at rest is strongly enhanced by a two step mechanism with intermediate K Kbar pi pi states. The relative yield of the phi production due to the resonant final state interaction decreases with increasing total energy of the p pbar system.

Tensor charge of the nucleon in lattice QCD

First results of lattice QCD simulation on the nucleon tensor-charge $\delta q$ are presented. From the quenched QCD simulations with the Wilson quark action at $\beta = 5.7$ on a 16$^3\times$ 20 lattice and on a $12^3\times 20$ lattice, we find (i) the connected part $\delta q_{con.}$ is determined with small statistical error, (ii) the disconnected part $\delta q_{dis.}$, which violates the OZI rule, is consistent with zero, and (iii) the flavor-singlet tensor charge $ \delta \Sigma (\mu^2 = 2 {\rm GeV}^2) = \delta u + \delta d + \delta s$ takes 0.562(88) at $\beta=5.7$, which is in contrast with the flavor-singlet axial charge $\Delta \Sigma = 0.1-0.3$.

Consequences of strangeness content in the nucleon for φ - meson production in NN̄ annihilation

Strong apparent violations of the OZI rule in annihilation reactions pp̄ → φX ( X = π 0 , η, p 0 , ω ) are discussed in the presence of a sizable ss̄ sea-quark component in the nucleon. An admixture of ss̄ quark pairs in the pp̄ wave function enables the direct coupling to the φ -meson in the annihilation channel without violating the OZI rule. Employing a nonrelativistic quark model, which incorporates the ss̄ admixture in the nucleon, we pursue the interpretation of the reactions pp̄ → X in terms of an effective “shake-out” quark line diagram. In the model calculation full account is taken of the spin-flavor-orbital structure of intial and final states, thereby employing the 3 P 0 -vertex for the description of the quark-antiquark transition dynamics. Estimates for the branching ratios of φX ( X = π 0 , η,p 0 , ω ) from atomic pp̄ states of orbital angular momentum L = 0, 1 are found to be strongly channel dependent in good agreement with the measured rates.

Recent results on OZI rule violations

Recent data from p̄p annihilation at LEAR indicate large violations of the OZI rule for certain final states. The final state dependance together with results on polarized lepton-nucleon scattering led to a model that assumes that there is a polarized s̄s component in the nucleon wave function. The data and this model will be presented and in the end a little phenomenological model is used to explain part of the strangeness enhancement that is seen in ultra-relativistic heavy ion reactions.

φφ excitation function at LEAR

The cross sections of the reactions pp → φφ, φK+K− and 4K± have been measured by the JETSET (PS202) experiment at CERN in the invariant mass range from 2.15 to 2.43 GeV/c2. A spin-parity analysis of the φφ system has been performed. The absolute value of the φφ cross section and the ratios σ(φφ)/σ(φK+K−), σ(φφ)/σ(4K±) are large, in marked violation of the OZI rule. Waves of quantum numbers JPC = 2++ give the dominant contribution near threshold.