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The main dynamical mechanisms of the reaction π − p → a 0 0 (980)n → π 0 ηn at high energies, currently investigated at Serpukhov and Brookhaven, are considered in detail. It is shown that the observed forward peak in its differential cross section can be explained within the framework of the Regge pole model only by the conspiring ρ 2 Regge pole exchange. The tentative estimates of the absolute π − p → a 0 0 (980)n → π 0 ηn reaction cross section at P π − lab = 18 GeV/c are obtained: σ ≈ 200 nb and, in the forward direction, dσ/dt ≈ 940 nb/GeV 2 . The contribution of the one pion exchange, which is forbidden by G-parity and which can rise owing to the f 0 0 (980)−a 0 0 (980) mixing, is also estimate. A role of the Regge cuts in the non-flip helicity amplitude is briefly examined and a conclusion is made that the contributions of the cuts have to be inessential in comparison with the conspiring ρ 2 Regge pole exchange.

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In this paper we present the fit to the recent high-statistical KLOE data on the φ → ηπ 0 γ decay. This decay mainly goes through the a 0 γ intermediate state. The obtained results differ from those of the previous fits: data prefer a high a 0 mass and a considerably large a 0 coupling to the KK.

Analysis of the nature of the φ → γπη and φ → γπ AbstractWe study interference patterns in the φ → (γa 0 + π 0 ρ) → γπη and φ → (γf 0 + π 0 ρ) → γπ 0 π 0 reactions. Taking into account the interference, we fit the experimental data and show that the background reaction does not distort the π 0 η spectrum in the decay φ → γπη everywhere over the energy region and does not distort the π 0 π 0 spectrum in the decay φ → γπ 0 π 0 in the wide region of the π 0 π 0 system invariant mass, m ππ > 670 MeV, or when the photon energy is less than 300 MeV. We discuss the details of the scalar meson production in the radiative decays and note that there are reasonable arguments in favor of the one-loop mechanism φ → K + K − → γa 0 and φ → K + K − → γf 0 . We discuss also distinctions between the four-quark, molecular, and two-quark models and argue that the Novosibirsk data give evidence in favor of the four-quark nature of the scalar a 0 (980) and f 0 (980) mesons.12.39.-x, 13.40.Hq, 13.65.+i

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