The recent discovery of a large CP violating asymmetry in KL-->pi+pi-e+e- mode has prompted us to seach for the associated KL-->pi 0 pi 0 e+e- decay mode in the KTeV-E799 experiment at Fermilab. In 2.7 x 10(11) K(L) decays, one candidate event has been observed with an expected background of 0.3 event, resulting in an upper limit for the KL-->pi 0 pi 0 e+e- branching ratio of 6.6 x 10(-9) at the 90% C.L.

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The KTeV/E799 experiment at Fermilab has searched for the rare kaon decay K(L)-->pi(0)e(+)e(-). This mode is expected to have a significant CP violating component. The measurement of its branching ratio could support the standard model or could indicate the existence of new physics. This Letter reports new results from the 1999-2000 data set. One event is observed with an expected background at 0.99+/-0.35 events. We set a limit on the branching ratio of 3.5x10(-10) at the 90% confidence level. Combining with the previous result based on the data set taken in 1997 yields the final KTeV result: BR(K(L)-->pi(0)e(+)e(-))<2.8x10(-10) at 90% C.L.

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We present a measurement of the charge asymmetry δ L in the mode K L → π ± e ∓ ν based on 298 million analyzed decays. We measure a value of δ L = (3322 ± 58(stat) ± 47(sys)) · 10 −6 , in good agreement with previous measurements and 2.4 times more precise than the current best published result. The result is used to place more stringent limits on CPT and ∆S = ∆Q violation in the neutral kaon system. PACS numbers: 11.30. Er, 13.25.Es, The charge asymmetry in K L semileptonic decays is deeply related to CP violation through neutral kaon mixing. TheBR(e + π − ) + BR(e − π + ) . Assuming ∆S = ∆Q and no CPT violation in the decayTo first order in the parameters that violate CP and CPT,The terms Y and Re(x −x) parameterize CPT violation in the ∆S = ∆Q and ∆S = −∆Q transitions respectively[1, 2]:In the Standard Model, the ∆S = ∆Q violation is CPTconserving and occurs in 2nd order weak decays. Estimates for |x| are in the range 10 −7 [3]. δ L is modified to order |x| 2 and will not be considered in this letter.