Bose-Einstein correlation and resonance production of pionic final states in anti-proton annihilation at rest

Bose-Einstein correlation is the name of the fact that in multiple-particle reactions, identical bosons are preferentially emitted under small relative momentum. This effect is understood as the symmetry of the quantum mechanical amplitude under boson exchange. It is the basis of several models that try to derive properties of the boson source, such as its size, from the observed correlations. They make certain assumptions on the source's chaoticity. Bose-Einstein correlation was discovered 1959 in antiproton annihilation and has since become an important tool in many areas of particle physics. The CPLEAR experiment at CERN studies neutral kaons produced by annihilating antiprotons at rest through the reactions $p\overline{p}\to K^-\pi+K^0$ and $p\overline{p}\to K^+\pi-\overline{K}^0$. These events make up only a few per thousand annihilation reactions. The vast majority are pionic final states, ideal for studying Bose-Einstein correlations of identical pions. We studied $p\overline{p}$ annihilations into $2\pi+2\pi, 2\pi+2\pi-\pi^0$ and $3\pi+3\pi-$. In a first step, the classical one-dimensional correlation functions could be reproduced successfully, though the correlation strength was in some cases up to twice as large as expected by the chaotic models. Next, an exclusive analysis method was developed, using the measured momenta of all particles in an event, not only that of one pion pair. The resulting double-differential distributions exhibit surprising features. The correlation of one pion pair strongly depends on the other pions present in the event, even after correcting for the trivial phase space effects. We found that the correlation of an identical pion pair is strongest when the other identical pairs in the event are also emitted with similar momentum. In some regions of phase space, the correlation strength reaches values around 10. This is in contradiction to the chaotic models of pion production. The 5-pion final state is an especially fertile study object, because the neutral pion does not take part in the correlations, and it can be used to vary the total energy of the charged pions. Special emphasis is also laid on the behavior of the different resonances apparent in the pion spectra. Without offering an exhaustive explanation of (he experimental findings, we point out the possibility that antiproton annihilation could be a fast, coherent process, and the observed boson correlations are due to the symmetrized wave function of resonances and final state interactions. A second focus of this thesis is the description of the CPLEAR detector readout system, and of a software driver developed for it.