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The excitation of the Roper resonance $N^*(1440)$ in $NN$ collisions leading to single and double pion production exhibits a structure in the energy dependence of the total cross section, which does not correspond to the usual opening of the $N^*(1440)$ production channel, but rather to the formation of dibaryon states with $I(J^P) = 0(1^+)$ and $1(0^+)$ at the $N^*(1440)N$ threshold. This is very similar to the situation at the $Delta(1232)N$ threshold, where meanwhile a number of dibaryonic resonances have been found.
The cross sections for the reactions pp -> p Lambda^0K^+ and pn -> n Lambda^0K^+ are calculated near threshold of the final states. The theoretical ratio of the cross sections R = sigma(pn -> n Lambda^0K^+)/ sigma(pp ->pLambda^0K^+) = 3 shows the e
The near-threshold n p -> d pi0 cross section is calculated in chiral perturbation theory to next-to-leading order in the expansion parameter sqrt{M m_pi}/Lambda_chi. At this order irreducible pion loops contribute to the relevant pion-production ope
An experimental study of $omega$ photoproduction on the proton was conducted by using the Crystal Ball and TAPS multiphoton spectrometers together with the photon tagging facility at the Mainz Microtron MAMI. The $gamma ptoomega p$ differential cross
Photoproduction of the $omega$ meson on the proton has been experimentally studied near the threshold. The total cross sections are determined at incident energies ranging from 1.09 to 1.15 GeV. The 1/2 and 3/2 spin-averaged scattering length $a_{ome
Observation of a narrow structure at $Wsim 1.68$ GeV in the excitation functions of some photon- and pion-induced reactions may signal a new narrow isospin-1/2 $N(1685)$ resonance. New data on the $gamma N to pi eta N$ reactions from GRAAL seems to r