A MEASUREMENT OF THE RATE OF FORMATION OF PION-MUON ATOMS IN LONG-LIVED NEUTRAL KAON DECAY

A pion and muon of opposite charge can be bound by their mutual attraction in the same way that a proton and electron are bound in a hydrogen atom. The realization that such "pi-mu atoms" are naturally formed in the decay of long-lived neutral K-mesons led to their discovery five years ago. At the same time, it was noted that pi-mu atoms could provide a means for probing the interaction between a pion and muon. The first step in this direction is to measure the probability of formation of pi-mu atoms in the decay of the K-long to pion, muon, and neutrino. This probability is proportional to the square of the pi-mu atom wave function at the origin. Thus, it reflects the nature of the force between a pion and muon.

This thesis describes the experiment in which we measured the rate of pi-mu atom formation to an accuracy of twelve per cent. The data were taken at the Fermi National Accelerator Laboratory using a high-energy kaon beam and wire-chamber spectrometer. Unbound pi-mu pairs from kaon decay were used for normalization. Our results are close to theoretical expectations.

In the same experiment, we observed decays of the K-mesons to final states which included photons. The study of the photons improved our understanding of the apparatus, and stimulated an investigation of rare kaon decays.