Decays of baryon resonances in the second and the third resonance region into Nπ0π0 are studied by photoproduction of two neutral pions off protons. Partial decay widths ofN and ∆* resonances decaying into ∆(1232)π,N(ππ)S ,N(1440)P11π, and N(1520)D13π are determined in a partial wave analysis of this data and of data from other reactions. Several partial decay widths were not known before. Inte...

The excited state lifetimes of DNA bases are often very short due to very efficient non-radiative processes assigned to the ππ*-nπ* coupling. A set of protonated aromatic diazine molecules (pyridazine, pyrimidine and pyrazine C4H5N2(+)) and protonated pyrimidine DNA bases (cytosine, uracil and thymine), as well as the protonated pyridine (C5H6N(+)), have been investigated. For all these molecul...

An elementary derivation is given of Cabibbo’s formula for subthreshold ππ charge-exchange (cx) interference in the three-meson final states produced in certain meson decays. The relative phase between the two interfering decay amplitudes from the ππ and ππ channels is found to depend almost entirely on the ClebschGordan coefficients appearing in the dominant isospin component of the final stat...

A new evaluation of the universal ππ scattering length relation is used to extract the ππ s-wave scattering lengths from threshold pion production data. Previous work has shown that the chiral perturbation series relating threshold pion production to ππ scattering lengths appears to converge well only for the isospin-2 case, giving a2 = −0.031±0.007m−1 π . A model-independent and data-insensiti...

We perform a dispersive theoretical study of the reaction γγ → ππ emphasizing the low energy region. The large source of theoretical uncertainty to calculate the γγ → ππ total cross section for √ s & 0.5 GeV within the dispersive approach is removed. This is accomplished by taking one more subtraction in the dispersion relations, where the extra subtraction constant is fixed by considering new ...

We perform a dispersive theoretical study of the reaction γγ → ππ emphasizing the low energy region. The large source of theoretical uncertainty to calculate the γγ → ππ total cross section for √ s & 0.5 GeV within the dispersive approach is removed. This is accomplished by taking one more subtraction in the dispersion relations, where the extra subtraction constant is fixed by considering new ...

The recent experimental data of both ππ/Kπ scattering and production processes, suggesting the existence of scalar σ and κ mesons, are reviewed. In many ππ/Kπ production processes the direct effects of their productions are observed, while they are, because of chiral symmetry, hidden in scattering processes, and now σ(500∼600) and κ(800∼900) are considered to be confirmed experimentally. The re...

We demonstrate that, together with the available experimental information , chiral symmetry determines the low energy behaviour of the ππ scattering amplitude to within very small uncertainties. In particular, the threshold parameters of the S–, P –, D– and F –waves are predicted, as well as the mass and width of the ρ and of the broad bump in the S–wave. The implications for the coupling const...