N. N. Achasov

On the nature of the scalar a(0)(980) and f(0)(980) mesons

A critical consideration of all unusual properties of the scalar a0(980) and f0(980) mesons is presented within the four-quark, two-quark, and molecular models. Arguments in favor of the four-quark model are given. Further experiments that could finally resolve this issue are discussed.

Radiative decays of Φ meson and nature of light scalar resonances

We show on gauge invariance grounds that a new threshold phenomenon has been discovered in the radiative decays φ → γa0 → γπ0η and φ → γf0 → γπ0π0. This enables us to conclude that production of the light scalar mesons a0(980) and f0(980) in these decays is caused by the four-quark transitions, resulting in strong restrictions on the large-Nc expansions of the decay amplitudes. The analysis shows that these constraints give new evidence in favor of the four-quark nature of a0(980) and f0(980) mesons.

Analysis of the φ → γπη and φ → γπ 0 π 0 decays

We study interference patterns in the φ → (γa0+π0ρ) → γπη and φ → (γf0+π0ρ) → γπ0π0 reactions. Taking into account the interference, we fit the experimental data and show that the background reaction does not distort the π0η spectrum in the decay φ → γπη everywhere over the energy region and does not distort the π0π0 spectrum in the decay φ → γπ0π0 in the wide region of the π0π0-system invariant mass, πππ > 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− → γa0 and φ → K+K− → γf0. We also discuss 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 a0(980) and f0(980) mesons.

Branching ratios for the decays of Ψ(3770) and ϒ(10580) mesons to a pair of light hadrons

AbstractThe branching ratios for the exclusive decays of the heavy quarkonia Ψ(3770) and ϒ(10580) to a pair of light mesons [π+π-, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4saiqadU% eagaqeaaaa!37A5!

Once more about gauge invariance in ϕ → γπ0π0

K\bar K

Dynamics of f 0(980)-resonance production in the reaction γγ → π + π −

, ρ(ω)π, ρ(ω)η, ρ(ω)η’, % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaam4samaaCa% aaleqabaGaaiOkaaaakiqadUeagaqeaaaa!388A!

A new look at the KLOE data on the decay φ→ηπ0γ

K^* \bar K