  We analyze the effect of spin degree of freedom on fidelity decay and entropy
production of a many-particle fermionic(bosonic) system in a mean-field,
quenched by a random two-body interaction preserving many-particle spin $S$.
The system Hamiltonian is represented by embedded Gaussian orthogonal ensemble
(EGOE) of random matrices (for time-reversal and rotationally invariant
systems) with one plus two-body interactions preserving $S$ for
fermions/bosons. EGOE are paradigmatic models to study the dynamical transition
from integrability to chaos in interacting many-body quantum systems. A simple
general picture, in which the variances of the eigenvalue density play a
central role, is obtained for describing the short-time dynamics of fidelity
decay and entropy production. Using some approximations, an EGOE formula for
the time ($t_{sat}$) for the onset of saturation of entropy, is also derived.
These analytical EGOE results are in good agreement with numerical
calculations. Moreover, both fermion and boson systems show significant spin
dependence on the relaxation dynamics of the fidelity and entropy.
