We report progress on calculating the KL-KS mass difference in lattice QCD. T he calculation is performed on a 2+1 flavor, domain wall fermion, 163×32
Nearby in the stack
en semble with a 421 MeV pion mass. We include only current-current operators and drop all disconnected and double penguin diagrams in the calculation. The calculation is made finite through the GIM mechanism by introducing a valence charm quark. The long distance effects are discussed separately for each of the two parity channels. Whil e we find a clear long distance contribution from the parity odd channel, the signal to noise ratio in the parity even channel is exponentially decreasing and the two-p ion state can be seen in only a subclass of amplitudes. We obtain the mass differenc e