QUANTUM NUMBER CONSERVATION IN STATISTICAL-MODELS AND ITS APPLICATIONTO P(P)OVER-BAR-ANNIHILATION AT REST

We investigate the role of exact quantum number conservation in small statistical systems and illustrate the consequences for ppBAR-annihila tion at rest. A group theoretical projection method is used to calcula te a restricted canonical partition function which consists only of st ates allowed by the conservation laws. Special emphasis is put on the conservation of isospin, total angular momentum, and C-, G-, and P-par ities. Our analysis of the partition function shows that it is increas ingly dominated by two-particle states as more of the conservation law s are included. The constraining effects on various multiplicity ratio s and the deviations from the unconstrained limit are discussed in det ail.