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We investigate colorless (mesonic) 3q − qq components in the nucleon and the Roper resonance N * (1440). Starting from constituent quarks and gluons we estimate the excitation of qq pairs in a gluon exchange model with the strong coupling constant extracted from a comparison with a non-perturbative resonating group calculation of the π, η, ρ and ω content of the nucleon. Applying the same model to the Roper resonance, we find as the most striking result a very strong scalar-isoscalar σ-content of the N * (1440) with a strength of the 3q − qq configurations comparable to the 3q component itself.Keywords: Constituent quark model, qq admixture, Roper resonance PACS: 12.39. Jh,12.39.Pn,14.20.Gk,21.45.+v Among the excited states of the nucleon, i.e. the baryon resonances in the continuum, the Roper resonance N * (1440) as the first excited state with the quantum numbers of the nucleon (J π , T ) = (2 ), plays a particular role. On the one side, parameterizing conventionally the Roper resonance as a system of three constituent quarks, most quark models predict the position of the Roper resonance as generally several hundred MeV above its experimental value [1][2][3]. On the other side, the N * (1440) seems to dominate the dynamics of coherent near threshold 2π production, both in pp → ppππ [4][5][6][7] and πA → ππA collisions [8,9], through the coupling to a virtual σ-meson (which subsequently then decays into two pions). Thus it is hoped that from the study of the Roper-induced dynamics ultimately shed light on the σ-degree of freedom -which is generally phrased as a 2π resonance with a mass and width of m σ ∼ Γ σ ∼ 550M eV [10] -both in the NN and in nuclear systems, where the σ-meson provides the medium range attraction; in addition, it might provide information of a partial restoration of chiral symmetry in dense nuclear matter * Supported in part by Forschungszentrum FZ Jülich (COSY) †

This is the first of a series of papers on a consistent model independent analysis of the complete experimental information on the reaction πN → ππN at pion momenta up to 500 MeV/c. The paper summarizes the theoretical approach and details of the computational procedure. The complete database on total cross sections in 5 ππN channels is given together with a critical discussion of their model independent analysis. * This work was funded by the Deutsche Forschungsgemeinschaft (DFG), Bundesminister für Forschung und Technologie (BMFT), and the Kernforschungsanlage Jülich (KFA) and Russian Ministry of Education Grant G13.018 0