To understand the various results on the N*(1440 MeV͒ resonance in a consistent way, the data on ␣-p scattering at E ␣ ϭ4.2 GeV were reanalyzed assuming projectile and target excitation, and their interference. A quantitative fit of the spectrum is obtained, assuming for the N* mass distribution a threshold modified Breit-Wigner shape with momentum-dependent width and resonance parameters M ϭ1390Ϯ20 MeV and ⌫ ϭ190Ϯ30 MeV. This, however, is not consistent with the data on -N scattering which, in general, require a higher resonance mass and a larger width. Both systems, ␣-p and -N, can be described consistently in a T-matrix formalism, assuming two structures in the P 11 (1440 MeV) resonance, from which only the first one is observed in ␣-p. For this structure the elastic -N width is small and the decay into the 2(s)-N channel is large. This strongly supports the conclusions drawn from ␣-p scattering. The second structure at higher mass has a strong decay into the ⌬ channel and can be well understood as a second-order excitation of the ⌬(1230 MeV). The two resonance picture of the P 11 (1440 MeV) resonance is supported by ␥-induced reactions; no evidence is found for the first N*, however, the second resonance is observed ͑although more or less obscured by nonresonant -⌬ production͒. A further crucial test of the existence of two structures in the Roper resonance is provided by exclusive ␣-p experiments; a N* decay pattern should be found quite different from -N with a very strong 2 decay.

No abstract

No abstract

Spectra of p-p and π -p scattering at beam momenta between 6 and 30 GeV/c have been reanalyzed. These show strong excitation of N * resonances, the strongest one corresponding to the "scalar" P 11 excitation (breathing mode) at m 0 = 1400 ± 10 MeV with = 200 ± 20 MeV. The result of a strong scalar excitation is supported by a large longitudinal amplitude S 1/2 extracted from e-p scattering. From exclusive data on p + p → ppπ + π − , a large 2π -N decay branch for the P 11 resonance of B 2π = 75 ± 20% has been extracted.The differential cross sections were described in a double-folding approach, assuming multigluon exchange as the dominant part of the effective interaction between the constituents of projectile and target. First, the parameters of the interaction were fitted to elastic scattering; then, with this interaction, the inelastic cross sections were described in the distorted wave Born approximation (DWBA). A good description of the data requires a surface peaked transition density, quite different from that of a pure radial mode. In contrast, the electron scattering amplitude S 1/2 is quite well described by a breathing mode transition density with radial node. This large difference between charge and matter transition densities suggests that in p-p scattering the coupling to the multigluon field is much more important than the coupling to the valence quarks. A multigluon (or sea-quark) transition density is derived, which also shows breathing, indicating a rather complex multiquark structure of N and N * including additional multigluon (or q 2nq 2n ) creation out of the ground state vacuum.

No abstract