Estudio unificado del espectro y propiedades de mesones pesados para energías por debajo y por encima de umbrales mesón-mesón

Resumen

We have pursued a comprehensive study of hidden-flavor heavy mesons for energies below and above open-flavor meson-meson thresholds by means of various theoretical schemes. In the first part of this study, we have used the Born-Oppenheimer (BO) approximation with potentials derived from quenched lattice QCD to analyze quarkonium and quarkonium hybrids. Then, we have used the wave functions calculated within the BO approximation to calculate decay widths of quarkonium and quarkonium hybrids states. Specifically, we have focused on decays by a single photon emission and strong decays to open-flavor meson-meson pairs. In the second part, we have adapted the diabatic framework from molecular physics to strong interactions in order to have a description of heavy mesons, made of quark-antiquark and meson-meson components, based on unquenched lattice QCD studies of string breaking. We have shown that the solutions of the diabatic Schrödinger equation for energies below threshold are bound states, which correspond to heavy mesons stable against decays to an open-flavor meson-meson pair. On the other hand, solutions above threshold are naturally interpreted as stationary scattering states. From them, heavy mesons states are obtained as resonances in the open-flavor meson-meson cross-sections. From a phenomenological point of view, there are two well-established experimental unconventional states that provide ideal case studies for, respectively, the BO approximation and the diabatic framework developed here. On the one hand the Upsilon(10860), whose mass and decay properties are compatible with those of a bottomonium state mixing with the lowest bottomonium hybrid, as calculated within a BO framework equipped with consistent quark pair creation models. On the other hand, the X(3872), which can be interpreted in the diabatic framework as a loosely bound open-charm meson-meson state with a compact charmonium core, as shown by a phenomenological calculation with an effective value of the energy gap. It should be pointed out that the diabatic framework is perfectly general in the sense that it can also be applied for a description of heavy-meson systems made of quarkonium and quarkonium hybrid components, such as the Upsilon(10860). The current limitation preventing this is the lack of lattice QCD input to derive the form of the mixing potential in such systems. Furthermore, the diabatic treatment is also suited for systems containing quarkonium, quarkonium hybrid, and meson-meson components as well. Hence, we conclude that a completely unified study of hidden-flavor mesons below and above open-flavor thresholds is possible by means of the diabatic approach. It is important to notice that the diabatic potential matrix treats on equal grounds the potentials of different channels (e.g.: quarkonium, meson-meson, hybrid,...) as well as the mixing potentials between them, so that the descriptions below and above threshold are connected seamlessly.