Measurements of Neutral Kaon Decays to Two Electron Positron Pairs

Abstract

OF THE DISSERTATION Measurements of Neutral Kaon Decays to Two Electron-Positron Pairs by Eva Halkiadakis Dissertation Director: Sunil V. Somalwar We observed 441 KL → e+e−e+e− events with a background of 4.2 events in the KTeV/E799II experiment at Fermilab. We present here a measurement of the KL → e+e−e+e− branching ratio (B), a study of CP symmetry and the first detailed study of the e+e− invariant mass spectrum in this decay mode. We used the e+e− mass spectrum in KL → e+e−e+e− to measure the KLγ∗γ∗ form factor which sheds light on the structure of KL → γ∗γ∗ transitions. The parameter αK∗ of Bergstrom, Masso and Singer [1] describes the relative strength of an intermediate pseudoscalar decay amplitude and a vector meson decay amplitude. We measured αeff K∗ = −0.14± 0.16stat ± 0.15syst, which takes into account both the form factor and radiative effects. This is the first form factor measurement using KL → e+e−e+e− . We also measured B(KL → e+e−e+e− ) = (3.72± 0.18stat ± 0.23syst)× 10−8. Using the the distribution of the angle between the planes of the e+e− pairs, we measured the CP parameters βCP = −0.23 ± 0.09stat ± 0.02syst and γCP = −0.09 ± 0.09stat ± 0.02syst for Mee > 8MeV . The parameter βCP is an indicator of the CP eigenstate of KL and γCP measures the amount of CP violation in the decay. We found that the 90% CL limit on |γCP| is < 0.21. The CP measurements are based on a restricted sample of 264 events, a factor of 10 more than the previous measurement.