RARE K DECAYS.

In the rush to explore the B system, one should not ignore the potential of rare K decays. The charged and neutral FCNC K {yields} {pi}{nu}{bar {mu}} decays are theoretically very clean, on a par with B {yields} {psi}K{sub S}, which measures {beta}, and much less problematic than B {yields} {pi}{pi} and B{sub s} {yields} K{sup +}K{sup -} or B{sub s} {yields} K*{sup +}K*{sup -} which have been proposed to measure {alpha} and {gamma} respectively. B(K{sup +} {yields} {pi}{sup +}{nu}{bar {nu}}), which in the Standard Model yields information on |V*{sub ts}V{sub td}|, is closely related to the ratio of B{sub d} - {bar B}{sub d} to B{sub s}-{bar B}{sub s}, mixing, which yields |V{sub td}/V{sub ts}|. It is essential to compare such clean measurements from the B and K sectors, because new physics is likely to manifest itself in apparent disagreements[12]. Measuring the branching ratios of K {yields} {pi}{nu}{bar {nu}} decays is a challenge, but the current proven reach in sensitivity for the charged mode and the prospect of measuring the neutral mode at AGS-2000 indicate that this window into flavor physics is on the verge of becoming an exploitable reality.