On collision duration in the presence of strong overlapping resonance levels

The time delay of wave packets in the case of strong overlapping resonances is discussed. It is shown that the duration of collision at very large level density is much larger than the lifetime of a separate level. It has a value of the order of 2π?/nD, where n is a number of open channels and D is the average level spacing. As a consequence, if the width Γ ? nD, the correlation length of cross section fluctuations must be of the order of nD but not Γ.