The mass of the $\pi^-$

The most precise values of the mass of the negatively charged pion have been determined from several measurements of X-ray wavelengths for transitions in pionic atoms at PSI. The Particle Data Group gives the average m_{\pi^-}mπ− = (139.570 61 \pm± 0.000 24) MeV/c^22.

Structure of double pionic atoms

We study theoretically the structure of double pionic atoms, in which two negatively charged pions (π-) are bound in the atomic orbits. The double pionic atom is considered to be an interesting system from the point of view of the multi bosonic systems. In addition, it could be possible to deduce valuable information on the isospin I = 2 π π interaction and the pion-nucleus strong interaction. In this paper, we take into account the π π strong and electromagnetic interactions, and evaluate the effects on the binding energies by perturbation theory for the double pionic atoms in heavy nuclei. We investigate several combinations of two pionic states and find that the order of magnitude of the energy shifts due to the π π interaction is around 10 keV for the strong interaction and around 100 keV for the electromagnetic interaction for the ground states.

Phenomenological nuclear density distributions

A recently proposed semiphenomenological density distribution for neutrons and protons in nuclei is discussed. This density was derived using the separation energies of the last neutron or proton. A com­parison is made with the symmetrised Fermi density distribution with parameters determined by fitting electron scattering experimental data and with a Fermi density with parameters coming from a recent anal­ysis of pionic atoms. Theoretical expressions for rms radii for neutron, proton and matter distributions are proposed, which give the average trend of the variation of these quantities as functions of Ν, Ζ and A respectively. To facilitate the use of the new density all the parameters needed in a practical application are tabulated for a series of nuclei. Some applications of the new density are also discussed.

From nucleons to nuclei (chiral soliton approach)

We discuss the properties of nucleons in nuclear matter and the properties of nucleonic systems in the framework of an in-medium modified Skyrme Lagrangian. The modification is achieved by introducing the medium functionals into the original Skyrme Model Lagrangian in free space[Formula: see text]. The parameters of the medium functionals are related to the low density phenomenology (i.e. to the pionic atoms3) from the one side and to the properties of nuclear matter at the saturation density [Formula: see text] from the other side. After fitting the parameters of the model, the extrapolations into the low density and high density regions showed that the model can successfully describe the Equations of State (EoS) of nuclear matter in the wide range of densities including the high critical densities existing in the interiors of neutron stars.