The KLOE measurement of phi radiative decays and of the ratio Gamma(Ks->pi+pi-(gamma))/Gamma(Ks->pi0pi0) are discussed. The first measurement aims at understanding the real nature of the scalar mesons a0 and f0, whose possible compositions are qq, qqqq, or KK molecule. The second measurement is related to the estimate of the phase shift difference delta0-delta2. Previous measurements were affected by a large uncertainty due to the presence of radiative effects which are correctly included in our analysis.

Based on a $J/\psi$ data sample of $7.8 \times 10^6$ events at BESI, the decay of $ J/\psi \to \bar{K}^*(892)^0 K^+ \pi^-$ is studied and a low mass enhancement, which is believed not coming from the phase space effect or background, is visible in the $K^+ \pi^-$ invariant mass spectrum recoiling against $\bar{K}^*(892)^0$. Partial wave analysis of this channel favors this low mass enhancement being a broad $0^{+}$ resonance with the mass and width of $771^{+164}_{-221}\pm 55$ MeV/c$^2$ and $220^{+225}_{-169} \pm 97$ MeV/c$^2$, respectively.

Inspired by large branching ratio (BR) of $B^{+}\to f_{0}(980)K^{+}$ decay measured by Belle recently, we propose that a significant evidence of the component of $n\bar{n}=(u\bar{u}+d\bar{d})/\sqrt{2}$ in $f_{0}(980)$ during its production could be demonstrated by exclusive $b\to c$ processes, in which %$f_{0}(980)$ is reconstructed the reconstructed $f_{0}(980)$ by the decays $\bar{B}\to D^{0(*)} \pi^{+} \pi^{-}(KK)$ and $\bar{B}\to J/\Psi \pi^{+} \pi^{-}(KK)$ is suggested. We predict the BRs of $\bar{B}\to D^{0(*)} (J/\Psi) f_{0}(980)$ to be ${\cal {O}}(10^{-4})$ (${\cal {O}}(10^{-5})$) while the unknown wave functions of $D^{(*)0}$ ($J/\Psi$) are chosen to fit the observed decays $\bar{B}\to D^{(*)0} \pi^{0} (J/\Psi K^{0(*)})$.

From Dalitz-plot analyses of $D^+\to\pi^-\pi^+\pi^+$ and $D^+\to K^-\pi^+\pi^+$ decays, we find evidence for light and broad scalar resonances sigma(500) and kappa(800). From a Dalitz-plot analysis of $D^+_s\to\pi^-\pi^+\pi^+$ decays, we measure the masses and decay widths of the scalar resonances f_0(980) and f_0(1370).

The nonleptonic weak decays of charmed mesons into a scalar meson and a pseudoscalar meson are studied. The scalar mesons under consideration are $\sigma$ [or $f_0(600)$], $\kappa$, $f_0(980)$, $a_0(980)$ and $K^*_0(1430)$. A consistent picture provided by the data implies that the light scalars below or near 1 GeV form an SU(3) flavor nonet and are predominately the $q^2\bar q^2$ states, while the scalar mesons above 1 GeV can be described as a $q\bar q$ nonet. Hence, we designate $q^2\bar q^2$ to $\sigma, \kappa, a_0(980), f_0(980)$ and $q\bar q$ to $K^*_0$. Sizable weak annihilation contributions induced from final-state interactions are essential for understanding the data. Except for the Cabibbo doubly suppressed channel $D^+\to f_0K^+$, the data of $D\to\sigma\pi, f_0\pi, f_0K, K^*_0\pi$ can be accommodated in the generalized factorization approach. However, the predicted rates for $D\to a_0\pi, a_0K$ are too small by one to two orders of magnitude when compared with the preliminary measurements. Whether or not one can differentiate between the two-quark and four-quark pictures for the $f_0(980)$ produced in the hadronic charm decays depends on the isoscalar $f_0-\sigma$ mixing angle in the $q\bar q$ model.

Weak decays of charm mesons has been used for studies of light quark spectroscopy, with particular emphasis on the J^{PC}=0^{++} states. Recent results on light scalars are summarized and some conceptual issues are discussed, especially the relation between charm decays and hadronic production.

We present a new model independent amplitude analysis of reaction pi(-)p->pi(-) pi(+)n measured at CERN at 17.2 GeV/c on polarized target using a Monte Carlo method for dipion mass 580-1080 MeV. The two solutions for measured moduli |Sbar|^2 and |S|^2 of the two S-wave transversity amplitudes Sbar and S show res onant behaviour below 800 MeV corresponding to a scalar resonance sigma(770). Simultaneous fits to |Sbar|^2 and |S|^2 include f_0(980). The CERN data on polar ized target supplemented by the assumption of analyticity of production amplitud es in dipion mass allow to determine the helicity amplitudes S_0 (a_1 exchange) and S_1 (pi exchange) from fitted transversity amplitudes. The sign ambiguity in sigma(770) contribution leads to 2 solutions. In the "down" solution sigma(770) is suppressed in the helicity flip amplitude S_1 and thus also in pi(-)pi(+)-> pi(-)pi(+) scattering. Most contribution of sigma(770) to pion production is in the nonflip amplitude S_0, or in pi(-)a_1(+)->pi(-)pi(+) scattering. In the "up" solution the situation is reversed. The "up" solution is excluded by unitarity in pipi scattering. The "down" solution, and thus the evidence for sigma(770), is in agreement with unitarity in both pi(-)pi(+)->pi(-)pi(+) and pi(-)a_1(+)-> pi(-)pi(+) scattering. There are 4 "down" solutions (1, 1bar), (2, 1bar), (1, 2bar) and (2, 2bar). The sigma(770) resonance manifests itself as a broad resonant structure at ~ 720 MeV in the flip amplitude |S_1|^2 in solutions (1, 1bar) and (2, 1bar). The contribution of sigma(770) to |S_1|^2 is small in solutions (1, 2bar) and (2, 2bar). The metamorphosis of a narrow sigma(770) in the nonflip amplitude S_0 into a broad resonant structure in the flip amplitude S_1 is a new phenomenon related to breaking of scale and chiral symmetry in QCD.

A model-dependent analysis of the hadronic substructure in tau- -> pi- pi- pi+ neutrino decay is reported. The decay is dominated by the process tau- -> a1(1260)- + neutrino, in which a1(1260)- -> rho0 pi- in an S-wave decay. Amplitudes involving a1(1260) decays into isoscalars, especially a_1(1260)- -> f0(600)pi-, are large. tau- -> pi- pi- pi+ neutrino decays via the pseudoscalar pi(1300)- are small. These results support the resonant substructure reported in the previously reported analysis of tau- -> pi0 pi0 pi- neutrino decay mode from the same CLEO II data sample.

Recent hadronic charm decay results from fixed-target experiments are presented. New measurements of the D0 to K-K+K-pi+ branching ratio are shown as are recent results from Dalitz plot fits to D+ to K-K+pi+, pi+pi-pi+, K-pi+pi+, K+pi-pi+ and D_s+ to pi+pi-pi+, K+pi-pi+. These fits include measurements of the masses and widths of several light resonances as well as strong evidence for the existence of two light scalar particles, the pipi resonance sigma and the Kpi resonance kappa.

We present recent results on light mesons based on Dalitz plot analyses of charm decays from Fermilab experiment E791. Scalar mesons are found to have large contributions to the decays studied, $D^+\to K^-\pi^+\pi^+$ and $D^+, D_s^+\to\pi^-\pi^+\pi^+$. From the $K\pi\pi$ final state, we find good evidence for the existence of the light and broad $\kappa$ meson and we measure its mass and width. We also discuss recently published results on the 3$\pi$ final states, especially the measurement of the $f_0$ parameters and the evidence for the $\sigma$ meson from $D^+\to\sigma\pi^+$. These results demonstrate the importance of charm decays as a new environment for the study of light meson physics.

The KLOE detector at DAFNE, the Frascati phi-factory, has collected about 30 pb^-1 by the end of 2000, corresponding to about 90 millions of phi(1020) mesons produced. The five photon final state has been exploited to study the rare decays of phi into f0(980) photon and a0(980) photon, with statistical accuracy never reached before. The preliminary results for these branching ratios, from a data sample of 17 pb^-1, are the following: BR(phi-->f0(980) photon)=(23.7 +- 0.6 (stat.) times 10^-5, BR(phi--> a0(980) photon)=(5.8 +- 0.5 (stat.)) times 10^-5. The systematic error is expected to be less than 10%, a precise evaluation is going on. For the ratio of the branching ratios of phi--> f0 photon to phi--> a0 photon we find 4.1 +- 0.4 (stat.).

We study the decay $\phi\to\gamma K^+K^-$ taking into account the scalar mesons production $\phi\to\gamma(f_0+a_0) \to\gamma K^+K^-$ and the final state radiation. We note that the relative sign between the final state radiation amplitude and the scalar meson production amplitude is fixed in the $K^+K^-$ loop model which describes data on the $\phi\to \gamma f_0\to\gamma\pi\pi$ and $\phi\to\gamma a_0\to\gamma\pi\eta$ decays. As consequence this model predicts the definite interference between the final state radiation and the scalar resonance production amplitudes. We calculate the mass spectra of the $\phi\to\gamma K^+K^-$ decay and the differential cross-sections for $e^+e^-\to\phi\to\gamma K^+K^-$ and for $e^+e^-\to\phi\to\gamma K^0\bar K^0$ reactions.

The inclusive production of the meson resonances $\rho^{0}(770)$, $f_0(980)$ and $f_2(1270)$ in neutrino-nucleus charged current interactions has been studied with the NOMAD detector exposed to the wide band neutrino beam generated by 450 GeV protons at the CERN SPS. For the first time the $f_{0}(980)$ meson is observed in neutrino interactions. The statistical significance of its observation is 6 standard deviations. The presence of $f_{2}(1270)$ in neutrino interactions is reliably established. The average multiplicity of these three resonances is measured as a function of several kinematic variables. The experimental results are compared to the multiplicities obtained from a simulation based on the Lund model. In addition, the average multiplicity of $\rho^{0}(770)$ in antineutrino - nucleus interactions is measured.

We analyze the pi pi production amplitudes in the excited Upsilon decay processes, Upsilon(2S)-->Upsilon(1S)pi+pi-, Upsilon(3S)-->Upsilon(1S)pi+pi- and Upsilon(3S)-->Upsilon(2S)pi+pi-, and the pi pi and KKbar production amplitudes in the charmonium decay processes, psi(2S)-->J psi pi+pi- and J psi-->phi pi+pi-, phi K+K-. The amplitudes are parametrized by the sum of Breit-Wigner amplitudes for the sigma and the other relevant particles and of the direct 2pi-production amplitude, following the VMW method. All the pi pi (and KKbar) invariant mass spectra are reproduced well with the sigma Breit-Wigner amplitude by using the common parameters, m_sigma=526^(+48)_(-37) MeV and Gamma_sigma =301^(+145)_(-100) MeV, which is almost consistent with the values obtained in our previous phase shift analyses. This strongly suggests the existence of light sigma-meson.

The results of analyses obtained in Part I are examined from the viewpoint of chiral symmetry. The mass spectra of pi pi system are widely believed to be suppressed generally near the threshold, because of the derivative coupling property of Nambu-Goldstone pi meson. However, this suppression does not hold in the processes with large energy release, and the steep increase from the pi pi threshold observed in the transition Upsilon (3S-->1S) is shown to be consistent with general constraints from chiral symmetry.