Structure of the scalar mesonsf0(980) anda0(980)

Abstract

We investigate the structure of the scalar mesons f 0 (975) and a 0 (980) within realistic meson-exchange models of the ππ and πη interactions. Starting from a modified version of the Jülich model for ππ scattering we perform an analysis of the pole structure of the resulting scattering amplitude and find, in contrast to existing models, a somewhat large mass for the f 0 (975) (m f 0 = 1015 MeV, Γ f 0 = 30 MeV). It is shown that our model provides a description of J/ψ → φππ/φKK data comparable in quality with those of alternative models. Furthermore, the formalism developed for the ππ system is consistently extended to the πη interaction leading to a description of the a 0 (980) as a dynamically generated threshold effect (which is therefore neither a conventional qq state nor a KK bound state). Exploring the corresponding pole 1 position the a 0 (980) is found to be rather broad (m a 0 = 991 MeV, Γ a 0 = 202 MeV). The experimentally observed smaller width results from the influence of the nearby KK threshold on this pole.

Jülich hyperon-nucleon model revisited

“…The correlations between the two mesons have been taken into account by means of ππ − KK amplitudes, determined in the field theoretical framework of Refs. [16][17][18], which provide an excellent description of empirical ππ data up to 1.3 GeV. With the help of unitarity and dispersion-theoretical methods, the baryonbaryon amplitudes for correlated ππ and KK exchange in the J P = 0 + (σ ) and J P = 1 − (ρ) t-channels have then been determined.…”

“…For details on the model and a comparision of the resulting ππ phase shifts with experimental values we refer the reader to Refs. [17,18].…”

“…[14], but was extended in a recent paper [15] by the Jülich group so that now a full and consistent microscopic derivation of correlated ππ exchange in various baryon-baryon (BB ) channels with strangeness S = 0, −1, and −2 is available. The starting point was a field theoretical model for both the NN → ππ Born amplitudes and the ππ and KK elastic scattering [16][17][18]. Thus, the KK channel is treated on an equal footing with the ππ channel in order to reliably determine the influence of KK correlations in the relevant t-channels.…”

Production of a0 mesons in pp and pn reactions

“…[4,5,6,7,8,9,10] and references therein). Different authors interpreted them as unitarized qq states or as four-quark cryptoexotic states or as KK molecules or even as vacuum scalars (Gribov's minions).…”

Coupled channel study of a0 resonances

“…Many conflicting view-points in which scalars are treated as qq or qqqq states, two-meson quasi-bound states and mixed states including glueballs coexist (see, for example, [8][9][10][11][12][13]). …”