  A two-slit interference of a massive particle in the presence of environment
induced decoherence is theoretically analyzed using a fully quantum mechanical
calculation. The Markovian Master equation, derived from coupling the particle
to a harmonic-oscillator heat bath, is used to obtain exact solutions which
show the existence of an interference. Interestingly, decoherence does not
affect the pattern, but only leads to a reduction in the fringe visibility.
