Electron Emission from Mesonic Atoms

The yield and energy distribution of electrons emitted from absorptions of stopping $K^{-}$ mesons in nuclear emulsions have been measured. In the electron energy range from 20-70 keV, the yield in the heavy elements Ag and Br has been analyzed to consist of 14% background electrons contributed by radioactivity, and 24% contributed by the radiationless Auger process in the $K$-mesonic atom. This Auger yield is considerably less than would be expected theoretically from existing conventional analyses of the $K^{-}$-mesonic atom cascade in Ag and Br. A possible explanation of the discrepancy is given in terms of a description involving Stark mixing in highly excited mesonic states. This gives rise to nuclear capture from the $f$ and $d$ angular momentum substates of highly excited levels. The probable effect of such a capture mechanism on the rate of multinucleon captures in nuclei is briefly discussed. Further experimental results are given on electron emission from $\pi$-mesonic atoms, and other data on $\mu$-mesonic and $\Sigma$-hyperonic atoms are also reviewed.