Measurements of the rare decay K_{L} -> e^{+} e^{-} e^{+} e^{-}

TL;DR

This paper reports the first detailed measurement of the rare decay K_{L} -> e^{+} e^{-} e^{+} e^{-}, including its branching ratio, CP parameters, and invariant mass spectrum, using data from Fermilab.

Contribution

The study provides the first detailed analysis of the e^{+} e^{-} invariant mass spectrum and precise measurements of CP parameters for this decay mode.

Findings

Branching ratio measured as (3.72 ± 0.18(stat) ± 0.23(syst)) × 10^{-8}

CP parameters beta_{CP} = -0.23 ± 0.09(stat) ± 0.02(syst), gamma_{CP} = -0.09 ± 0.09(stat) ± 0.02(syst)

First detailed study of the e^{+} e^{-} invariant mass spectrum in this decay

Abstract

We observe 441 K_{L} -> e^{+} e^{-} e^{+} e^{-} candidate events with a background of 4.2 events and measure B(K_{L} -> e^{+} e^{-} e^{+} e^{-}) = (3.72 \pm 0.18(stat) \pm 0.23(syst)) \times 10^{-8} in the KTeV/E799II experiment at Fermilab. Using the distribution of the angle between the planes of the e^{+} e^{-} pairs, we measure the CP parameters beta_{CP} = -0.23 \pm 0.09(stat) \pm 0.02(syst) and gamma_{CP} = -0.09 \pm 0.09(stat) \pm 0.02(syst). We also present the first detailed study of the e^{+} e^{-} invariant mass spectrum in this decay mode.