  Multiparticle symmetrization effects are contributions to the spectra of
Bose-symmetrized states which are not the product of pairwise correlations.
Usually they are neglected in particle interferometric calculations which aim
at determining the geometry of the boson emitting source from the measured
momentum distributions. Based on a method introduced by Zajc and Pratt, we give
a calculation of all multiparticle symmetrization effects to the one- and
two-particle momentum spectra for a Gaussian phase space distribution of
emission points. Our starting point is an ensemble of N-particle
Bose-symmetrized wavefunctions with specified phase space localization. In
scenarios typical for relativistic heavy ion collisions, multiparticle effects
steepen the slope of the one-particle spectrum for realistic particle phase
space densities by up to 20 MeV, and they broaden the relative momentum
dependence of the two-particle correlations. We discuss these modifications and
their consequences in quantitative detail. Also, we explain how multiparticle
effects modify the normalization of the two-particle correlator. The resulting
normalization conserves event probabilities, which is not the case for the
commonly used pair approximation. Finally, we propose a new method of
calculating Bose-Einstein weights from the output of event generators, taking
multiparticle correlations into account.
