Abstract
In recent years, the discovery in quarkonium spectrum of several states not predicted by the naive quark model has awakened a lot of interest. A possible description of such states requires the enlargement of the quark model by introducing quark-antiquark pair creation or continuum coupling effects. The unquenching of the quark models is a way to take these new components into account. In the spirit of the Cornell Model, this is usually done by coupling perturbatively a quark-antiquark state with definite quantum numbers to the meson-meson channel with the closest threshold. In this work we present a method to coupled quark-antiquark states with meson-meson channels, taking into account effectively the nonperturbative coupling to all quark-antiquark states with the same quantum numbers. The method will be applied to the study of the X(3872) resonance and a comparison with the perturbative calculation will be performed.
Highlights
Constituent quark models (CQM) have been extremely successful in describing the properties of hadrons such as the spectrum and the magnetic moments
The baryon wave function consists of a zerothorder three-valence quark configuration plus a sum over baryon-meson loops
The method is applied to the coupling of the X(3872) resonance to the 1++ qq states and the results were compared with those of the perturbative calculation of Ref. [13]
Summary
Constituent quark models (CQM) have been extremely successful in describing the properties of hadrons such as the spectrum and the magnetic moments. Van Beveren and Rupp [4, 5] showed the influence of continuum channels on the properties of hadrons, in a model which describes the meson as a system of one or more closed quark-antiquark states in interaction with several two meson channels. Bijker and Santopinto [6] developed an unquenched quark model for baryons, in which a constituent quark model is modified to include, as a perturbation, a QCDinspired quark-antiquark creation mechanism Under this assumption, the baryon wave function consists of a zerothorder three-valence quark configuration plus a sum over baryon-meson loops. Afterwards, the contribution of each “quenched” state is determined by expanding the obtained wave function in a bare quark-antiquark base In this way, one incorporates from scratch all possible qq states and allows the deformation of the bare qq wave function due to interaction with the meson-meson channels.
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