Search for the Rare DecayKL→π0e+e−

Abstract

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.

Probing light thermal dark matter with a Higgs portal mediator

“…The gaps in the coverage near m φ ∼ 2 − 3 GeV are regions vetoed by the search criteria in [58,59]. In the same parameter space, we also show bounds from measurements of the K L → π 0 + − branching ratio [60,61] as extracted in [57] for light scalars using the analysis to bound pseduoscalar mediators in [40].…”

New Physics Implications of Recent Search for KL→π0νν¯Kitahara1, Okui2, Pérez3 et al. 2020Phys. Rev. Lett.7911260View full textAdd to dashboardCite

“…Assuming lepton flavor universality, the above operators can be sensitive to CP-violating flavor changing neutral current such as K L → π 0 + − ( = e, µ) and K S → µ + µ − , whose branching ratios are experimentally bounded as ∼ < (a few) × 10 −10 [21][22][23]. In light…”

Dark forces coupled to nonconserved currents

“…However, this weak-isospin breaking in the EFT means that π ± → e ± νX decays, as discussed in section III D, are energy-enhanced. In the model of [9], in which X has dimension-4 couplings to electrons, but not to pions or neutrinos, the induced [50,53,54], B → KX (blue) [45][46][47][48][49], Z → Xγ (red) [30][31][32][33][34], very displaced decays at the CHARM proton beam dump experiment [58], and monojets [98]. The enhanced K → πX decays result in larger X production than computed in naive analyses [59,60].…”