Pi meson

Deser S., Goldberger M. L., Baumann K. and Thirring W. Energy Level Displacements in Pi-Mesonic Atoms, Phys. Rev. 96, 774-776 (1954) Anagnostopoulos D. F. et al., Precision measurements in pionic hydrogen, Nucl. Phys. A 721, 849-852 (2003). 

At still higher energies, let us say 100 MeV and beyond, we move from nuclear physics to the domain of particle physics. In this arena unstable particles are created which release gamma photons as part and parcel of their decay process. When two protons of very high energy run into one another, they sometimes generate neutral pi mesons which then decay to gamma photons. 

BOSONS. Those elementary particles for which there is symmetry under intra-pair production. They obey Bose-Einstein statistics. Included are photons, pi mesons, and nuclei with an even number of particles. (Those particles for which there is antisymmetry fermions.) See Mesons Particles (Subatomic) and Photon and Photonics. 

Metastable muonium atoms in the 2s state have been produced with a beam foil technique at LAMPF and at the Tri University Meson Physics Facility (TRI-UMF) at Vancouver, Canada. Only moderate numbers of atoms could be obtained. The velocity resonance nature of the electron transfer reaction results in a muonium beam at keV energies. Very difficult and challenging experiments using electromagnetic transitions in excited states, particularly the 2 Si/2 2 Pi/2 classical Lamb shift and 2 Si/2-2 P3/2 splitting could be induced with microwaves. However, the achieved experimental accuracy at the 1.5 % level [18,19,20], does not represent a severe test of theory yet. 

A-z-k) in the lab system, respectively, wave function of TT+TT bound state with the Coulomb potential only squared at the origin with the principal quantum number n and the orbital momentum Z = 0, Pb is the Bohr momentum in 2, dan/dpidp2 is the double inclusive production cross section for tt+tt -pairs from short lived sources without taking into account 7r+7T Coulomb interaction in the hnal state, p and P2 are the 7t+ and 7t momenta in the lab system. The momenta of 7t+ and 7t mesons obey the relation Pi P2 The A2W are produced in states with different principal quantum numbers n and are distributed according to n Wi = 83%, W2 = 10.4%, W3 = 3.1%, W >4 = 3.5%. The probability of A2tt production in K, K, p, p, xp and T mesons decay were calculated in [34]. 

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