Extracting short-distance physics from KL,S→π0e+e− decays Original Research Article

We present a new analysis of the rare decay KL→π0e+e− taking into account important experimental progress that has recently been achieved in measuring KL→π0γγ and KS→π0e+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 KS→π0e+e−, and a reanalysis of the CP-conserving part. The latter is shown to be negligible, based on experimental input from KL→π0γγ, 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(KL→π0e+e−)=(3.2+1.2−0.8)×10−11 in the Standard Model, dominated by CP violation with a sizable contribution (∼40%) from the direct effect, largely through interference with the indirect one. Methods to deal with the severe backgrounds for KL→π0e+e− using Dalitz-plot analysis and time-dependent KL–KS interference are also briefly discussed.