Speaker
Dr
Andreas Winhart
(Institut fuer Physik, Universitaet Mainz)
Description
The main goal of the NA48 experiment at the CERN SPS has been the
search for direct CP violation (CPV) in kaon decays. The observable
$\eta_{+-}$ is related to the parameters of indirect and direct CPV
($\eta_{+-} = \varepsilon + \varepsilon^\prime$) and defined as
the CP
violating amplitude ratio of the neutral kaon decaying into two
charged pions: $\eta_{+-} = A(K_L \to \pi^+\pi^-)/A(K_S \to
\pi^+\pi^-)$. NA48 has determined $|\eta_{+-}|$ via the
measurement of
the ratio of decay rates $\Gamma(K_L \to \pi^+\pi^-)/\Gamma(K_L \to
\pi e \nu)$. The data were taken during a dedicated run in 1999 using
a pure $K_L$ beam. The analysis is based on 47000 $K_L \to
\pi^+\pi^-$
and five million $K_L \to \pi e \nu$ decays.
Complementary with $\varepsilon^\prime/\varepsilon$, the observable
in the charged kaons sector is the asymmetry $A_g = (g^+ -
g^-)/(g^+ +
g^-)$ of the linear slope parameter $g$ in the Dalitz plot of $K^\pm
\to 3\pi$ decays. Any non-zero value of $A_g$ would reflect evidence
for direct CPV. SM predictions for the charge asymmetry give an upper
limit of a few $10^{-5}$, while theoretical calculations involving
processes beyond the SM do not exclude substantial enhancements of
$A_g$. The NA48/2 experiment used simultaneous $K^+/K^-$ beams, and
from the data samples taken in 2003 and 2004, $3.11 \times 10^9 K^\pm
\to \pi^\pm\pi^+\pi^-$ and $9.13 \times 10^7 K^\pm \to
\pi^\pm\pi^0\pi^0$ were selected. The charge asymmetry parameter
$A_g$
was determined with a total uncertainty of $\sim 2\times 10^{-4}$ for
each mode, ten times more accurate than previous measurements.
Primary author
Dr
Andreas Winhart
(Institut fuer Physik, Universitaet Mainz)
