  The nu=5/2 fractional quantum Hall state is studied numerically, directly
including the effects of electron scattering between neighboring Landau levels.
Significant reduction of the excitation gap caused by the LL mixing explains
the discrepancy between earlier calculations and experiments. On the other
hand, LL mixing also considerably reduces overlaps with the Moore--Read
wavefunction, raising a question of the actual realization of nonabelian
quasiparticles in present experiments.
