Publisher's Note: Mesonic content of the nucleon and the Roper resonance [Phys. Rev. C 75, 067001 (2007)]

Abstract

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) †

Experimental and theoretical backgrounds for generation of dibaryons inNNand3Ninteractions

“…The above similarities manifest much further in decays mode. In fact, as it was found on recent detailed studies for the Roper decay modes [35,30,31], the scalar-isoscalar 2π channel plays a leading role in the Roper decay, contrary to the previous belief about dominance for R → ∆ + π decay mode (we do not discuss here the well known π channel decay into the nucleon ground state). In line with this, the interpretation and explanation for ABC-puzzle should also be related to the dibaryon decay into 2π channel (with σ-meson generation).…”

The N*(1710) as a resonance in the ππN system

“…There are many findings which support this idea, e.g., a strong σN coupling to the Roper resonance reported in [21,22], an important contribution from the two meson cloud to the masses of the SU(3) antidecuplet members found in [23], and a good reproduction of the data on the Σπ distribution in the π − p → K 0 Σπ reaction by taking the ππN decay channel of the N * (1710) into account [24]. Hence, a study of the three-body structure of these resonances could shed more light on their properties.…”

Valence quark contributions for theγN→P11(1440)form factors

“…The γN → P 11 (1440) transition amplitudes have been studied in several ways: treating the Roper as a quarkgluon system [12], a pure valence quark system [4,[13][14][15][16][17][18], and a valence quark system dressed by qq pairs [19][20][21][22][23]. Relativity has proven to be very important, not only for a large Q 2 , but also for the region Q 2 ∼ 0.…”