Spectrum and Decays of Hadronic Atoms

Abstract

Using non relativistic effective Lagrangian techniques, we analyze the hadronic decay of the pi+pi- atom and the strong energy-level shift of pionic hydrogen in the ground state. We derive general formulae for the width and level shift, valid at next-to-leading order in isospin breaking. The result is expressed in terms of hadronic threshold amplitudes that include isospin-breaking effects. In order to extract isospin symmetric scattering lengths from the data, we invoke chiral perturbation theory, that allows one to relate the scattering lengths to the threshold amplitudes.

8 pages. Talk given at ``8th International Symposium on Meson-Nucleon Physics and the Structure of the Nucleon (MENU99)'', Zuoz, Switzerland, August 16-20, 1999