Violation of CPT and Quantum Mechanics in the K0--K0bar System

We reconsider the model of quantum mechanics violation in the $\ko$--$\kob$ system, due to Ellis, Hagelin, Nanopoulos, and Srednicki, in which \cp- and \cpt-violating signatures arise from the evolution of pure states into mixed states. We present a formalism for computing time-dependent asymmetries in this model and show that present data constrains its parameters significantly. In the future, this model will be put to very stringent tests at a $\phi$ factory. We present the theory of these tests and show the relation between particular $\phi$ decay correlations and the parameters of quantum mechanics violation.