Bulg. J. Phys. vol.44 no.1 (2017), pp. 068-075

Collisional Effects on the Dipole Transitions of Pionic Helium

B. Obreshkov
Institute for Nuclear Research and Nuclear Energy, Bulgarian Academy of Sciences, Sofia 1784, Bulgaria
Abstract. The collision-induced shift and broadening of selected dipole transition lines of pionic helium in gaseous helium at low temperatures up to T=12 K and pressure up to a few bar are calculated in the approximation of binary collisions. We predict blue shifts of the resonance frequencies of the unfavored and red shifts for the favored transitions. The collisional Stark mixing and quenching of the metastable states of the pionic atom is found to be unlikely at thermal energies due to the large separation between the energy levels in the pionic atom within the same energy shell.

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