Pion Multiplicity Distribution in Proton-Antiproton Annihilation at Rest

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The pion multiplicity distribution is widely believed to reflect the statistical aspects of pp annihilation at rest. We try to reproduce it in a grand canonical picture with explicit conservation of electric charge, isospin, total angular momentum, and the parity quantum numbers P, C, and G via the projection operator formalism. Bose statistics is found to be non-negligible, particularly in fixing the interaction volume. The calculated pion multiplicity distribution for nπ = 5 turns out to depend strongly on the conservation of the angular momentum and connected quantum numbers, as well as on the spin state occupation in S-wave annihilation. However, the empirical Gaussian pion multiplicity distribution cannot be reproduced. This calls in question either the statistical ansatz or the rather old data themselves.