Meson electromagnetic form factors

The electromagnetic structure of the pseudoscalar meson nonet is completely described by the sophisticated Unitary&Analytic model, respecting all known theoretical properties of the corresponding form factors.Comment: Invited talk on 12th International Workshop on Meson Production, Properties and Interaction Krakow, Poland, 31 May - 5 June 2012. (11 latex pages, 7 eps figures

One-photon decay of the tetraquark state X(3872)→γ+J/ψX(3872) \to \gamma + J/\psi in a relativistic constituent quark model with infrared confinement

We further explore the consequences of treating the X(3872) meson as a tetraquark bound state by analyzing its one-photon decay X => \gamma + J/psi in the framework of our approach developed in previous papers which incorporates quark confinement in an effective way. To introduce electromagnetism we gauge a nonlocal effective Lagrangian describing the interaction of the X(3872) meson with its four constituent quarks by using the P-exponential path-independent formalism. We calculate the matrix element of the transition X => \gamma+ J/psi and prove its gauge invariance. We evaluate the X=> \gamma + J/psi decay width and the longitudinal/transverse composition of the J/psi in this decay. For a reasonable value of the size parameter of the X(3872) meson we find consistency with the available experimental data. We also calculate the helicity and multipole amplitudes of the process, and describe how they can be obtained from the covariant transition amplitude by covariant projection.Comment: 13 pages, 5 figures. Typos corrected, version matching the one published in PR