Extracting short-distance physics from KL,S → π0e+e- decays

We present a new analysis of the rare decay K-L --> pi(0)e(+)e(-) taking into account important experimental progress that has recently been achieved in measuring K-L --> pi(0)gammagamma and K-S --> pi(0)e(+)e(-). This includes a brief review of the direct CP-violating component, a calculation of the indirect CP-violating contribution, which is now possible after the measurement of K-S --> pi(0)e(+)e(-). and a reanalysis of the CP-conserving part. The latter is shown to be negligible, based on experimental input from K-L --> pi(0)gammagamma, a more general treatment of the form factor entering the dispersive contribution, and on a comparison with the CP-violating rate, which can now be estimated reliably. We predict B(K-L --> pi(0)e(+)e(-)) (3.2(-0.8)(+1.2)) X 10(-11) in the Standard Model, dominated by CP violation with a sizable contribution (similar to40%) from the direct effect, largely through interference with the indirect one. Methods to deal with the severe backgrounds for K-L --> pi(0)e(+)e(-) using Dalitz-plot analysis and time-dependent K-L-K-S interference are also briefly discussed. (C) 2003 Elsevier B.V. All rights reserved.