Separation of quantum correlated particles by a heat bath

We consider the action of a heat bath on one particle of a pair of spin-$\frac{1}{2}$ particles in a singlet state. The related relaxation effects are described by the Pauli master equation. We show that the density matrix of the two-particle system tends toward a product. The interpretation of this result is, however, complicated by the nonuniqueness of the decomposition of a given density matrix into pure states. To circumvent this difficulty we study separately the terms describing the fluctuations and the friction. The first one does not modify the correlations, although it screens them but the second one separates the systems. The action of a fluctuating magnetic field on one particle of a correlated pair is also investigated.