UNITARITY OF NEUTRAL KAON SYSTEM

In a neutral kaon system, where we always use a non-hermitian Hamilton ian for convenience of treating decay processes, unitarity seems to be lost. If we take decay channels (pi pi, pi pi pi, pi l nu, ..., etc.) into account, however, the Hamiltonian of the entire system must be h ermitian. We attempt to derive an effective Hamiltonian with respect t o only KO and (K) over bar(0) states, starting from a hermitian Hamilt onian. For brevity, we take only a pi pi state into account as the dec ay channel in this paper. We cannot avoid an oscillation between K-0, (K) over bar(0) and pi pi states if we start from a hermitian Hamilton ian whose states all have discrete energy levels. We therefore treat t he pi pi state more appropriately as to have a continuous energy spect rum to achieve the decay of K-0 and (K) over bar(0) into pi pi. As a c onsequence, we find a time evolution which differs from what we expect in the conventional method immediately after the decay starts, though it recovers Fermi's golden rule for a sufficiently long time scale.