Role of quasiparticles in the growth of a trapped Bose-Einstein   condensate
  A major extension of the model of condensate growth introduced by us is made to take account of the evolution of the occupations of lower trap levels (quasiparticles) by scattering processes, and of the full Bose-Einstein formula for the occupations of higher trap levels, which are assumed to have a time independent occupation. The principal effect is a speedup of the growth rate by somewhat less than an order of magnitude, the precise value depending on the the assumptions made on scattering and transition rates for the quasiparticle levels. 
C.W. Gardiner, M.D. Lee, R.J. Ballagh, M.J. Davis, and P. Zoller