X Rays fromμ,π,κ, andΣ−Capture in the Light Elements

A search for x rays from the capture of kaons in helium has disclosed neither $K$- nor $L$- series radiation; the upper limit of the x-ray yield is in the range 7-10%. This contradicts results of an earlier measurement, but is in better agreement with related data on kaon-helium scattering. In the same experimental arrangement, the yields of pionic and muonic x rays in helium were also measured. We find anomalously low yields, accompanied by intensity distributions of the $K$-series members in disagreement with the conventional cascade picture of a predominantly circular set of orbits. Monte Carlo cascade calculations could not duplicate the observed results unless weak Stark mixing, in the form of "sliding transitions" ($n,l\to n,l\pm 1$), was added. Agreement with observation was achieved in muonic, pionic, and kaonic atoms with a single value for the parameter describing the strength of the Stark mixing. Yields and energies of kaonic x rays in other light elements, Li, Be, and C, were also measured. Yields of x rays from muonic and pionic capture in these elements were remeasured also, and cascade calculations like those for helium repeated. In these elements the addition of Stark mixing is not needed to achieve agreement with experiment. In the pionic atoms $2p$-state absorption rates, and in kaonic atoms $3d$-state absorption rates for He, Li, Be, and C can be derived from the experimental data and compared with theoretical values, with good agreement. In addition to the identifiable kaonic transition lines also observed by Wiegand and Mack, additional lines not ascribable to kaonic atoms were found in all three elements. After careful consideration of possible origins of these lines, we ascribe the two lithium lines to $M\alpha$ and $M\beta$, and the Be line to $M\alpha$ transitions in $\Sigma$-hyperonic atoms. Such atoms are formed if ${\Sigma }^{-}$ hyperons from kaon capture (whose abundance is about 15%) are slowed down and stopped in the target. The observed yields and energies are consistent with this interpretation, and with no other we have been able to invent. A line in C, however, cannot be ascribed either to kaonic or $\Sigma$ atoms, and appears to be a pionic $L\alpha$. Why such a line appears only in C is not understood.