PARAMETERS FOR ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ DECAYS

These are the $\mathit CP$-violating parameters in the $\phi $ distribution, where $\phi $ is the angle between the planes of the two ${{\mathit e}^{+}}{{\mathit e}^{-}}$ pairs in the kaon rest frame:
$\mathit d\Gamma /\mathit d\phi $ ${}\propto$ 1 +$\beta _{\mathit CP}$ cos $(2\phi )$ + $\gamma _{\mathit CP}$ sin$(2\phi )$
where $\beta _{CP}$ = $-0.20$ and $\gamma _{CP}$ = 0 values correspond to no $\mathit CP$ violation.

$\beta _{\mathit CP}$ from ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$

INSPIRE   PDGID:
S013BCP
VALUE EVTS DOCUMENT ID TECN  COMMENT
$\bf{ -0.19 \pm0.07}$ OUR AVERAGE
$-0.13$ $\pm0.10$ $\pm0.03$ 200 1
LAI
2005B
 NA48
$-0.23$ $\pm0.09$ $\pm0.02$ 441
ALAVI-HARATI
2001D
 KTEV $\mathit M_{ {{\mathit e}} {{\mathit e}} }>$8 MeV/$\mathit c{}^{2}$
1  LAI 2005B obtains $\beta _{CP}$ = $-0.13$ $\pm0.10~$(stat) if $\gamma _{CP}$ = 0 is assumed.
Conservation Laws:
$\mathit CP$ VIOLATION OBSERVED
References:
LAI 2005B
PL B615 31 Measurement of the ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$ Decay Rate
ALAVI-HARATI 2001D
PRL 86 5425 Measurements of the Rare Decay ${{\mathit K}_L^0}$ $\rightarrow$ ${{\mathit e}^{+}}{{\mathit e}^{-}}{{\mathit e}^{+}}{{\mathit e}^{-}}$