Study of the OZI selection rule in hadronic processes

Abstract

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 P π − =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 2 ∆θ 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 ss component in the quark structure of protons. : 13.85.Fb; 14.40.Cs; 14.40.Ev PACS The OZI ruleThe selection rule for connected and disconnected quark diagrams that is referred to as the OZI rule has been known for a long time [1][2][3]. According to this rule, processes involving the annihilation or creation of a quark-antiquark pair entering into the composition of the same hadron are forbidden or, strictly speaking, strongly suppressed. The OZI rule may be illustrated by the diagrams for the production and decay of the vector mesons ω and φ (see Fig. 1).Let us consider exclusive reaction of qq pair production A + B → C 1 + C 2 + ... + C n + (qq) (q = u; d; s) with particles A, B, C i without strange quarks (see [4]). The ratio of amplitudes of the corresponding reactionsdetermines the violation of the OZI rule in these processes (the OZI rule demands Z = 0). It is well known that neutral mesons from meson nonets are the mixture of SU(3) octet and singlet states For vector meson nonetHere θ V is a mixing angle for vector nonet; α (or3 o is an ideal mixing angle (for this ideal mixing |φ >= −|ss >; |ω >= 1 √ 2 (uū + dd) >), as on diagrams in Fig. 1).For the ratio of amplitudes of φ and ω production the following expression was derived [4]:Thus the ratio of corresponding cross sections is Fig. 1. Diagrams for: a,b OZI-allowed and c,d OZI-suppressed production and decay processes: a reaction π − + p → ω + n, b decay ω → π + π − π 0 (connected quark diagrams); c reaction π − + p → φ + n, and d decay φ → π + π − π 0 (disconnected quark diagrams)where f is a kinematical phase space correction factor. Because the phase of β is unkown it is only possible to estimate the limits for the OZI violation factor |Z|:Many measurements of the R ratio and testing of the OZI rule in different reactions were made in the last thirty years. It is the generalization of the OZI rule for the processes with charmed quarks which explaines the anomalously small decay width of the J/ψ particle, representing a bound cc state (in analogy with φ meson). Recent years have seen a revived interest in the OZI rule. First, in...

On the current status of OZI violation in πN and pp reactions

“…Furthermore, since additional experimental results [19,20] are available for the ratio of the φ/ω total or differential cross sections above 8 GeV bombarding energy, we also show this ratio calculated with Eq. (5) in Fig.8 as a function of the incident proton energy.…”

“…Experimental data are taken from Refs. [7,6,19,20]. The solid line shows the result calculated with the energy independent ratio |Mω|/|M φ |=8.3, while the dashed area indicates the parent standard deviation.…”

Search for ${\rm\Theta}(1540)^ + $ in the exclusive proton-induced reaction ${\rm p + {C(N)\to \Theta^ + \bar{K}^0 + {C}(N)}}$ at the energy of 70 GeV

“…The analysis, done in [39], allows to extrapolate to our energy, giving the value (36 ± 4)/2 = 18 ± 2 µb/nucleon for ωp forward hemisphere production cross section. Using then cross section ratio σ φ /σ ω = (1.55 ± 0.31) × 10 −2 , measured in our study of OZI-rule [40], we arrived at the prediction for φp production cross section σ φp = 279 ± 64 nb/nucleon. This value is close, but somewhat higher than σ meas = 202 nb/nucleon (Table 2).…”

Measurement of OZI rule violation and spin alignment inϕandωproduction at COMPASS

“…In Ref. [12] the SPHINX collaboration argued that the OZI rule may not be valid in case of a dominant resonance production part of the cross section. Analogue to Ref.…”

“…Analogue to Ref. [12], the momentum of the vector meson in the pV centre-of-mass frame was required to be larger than 1 GeV/c to exclude the mass region which show obvious resonant structures in the ω case. In agreement with SPHINX, we observe an increase of the degree of OZI violation to a factor of 6 (cf.…”