New high statistics measurement of Ke4K_{e4} decay form factors and ππ\pi\pi scattering phase shifts

We report results from a new measurement of the $K_{e4}$ decay $K^{\pm} \rightarrow \pi^{+}\pi^{-}e^{\pm}\nu$ by the NA48/2 collaboration at the CERN SPS, based on a partial sample of more than 670000 $K_{e4}$ decays in both charged modes collected in 2003. The form factors of the hadronic current (F, G, H) and $\pi\pi$ phase difference ($\delta=\delta_{s}-\delta_{p}$) have been measured in ten independent bins of the $\pi\pi$ mass spectrum to investigate the variation. A sizeable acceptance at large $\pi\pi$ mass, a low background and a very good resolution contribute to an improved experimental accuracy, a factor two better than in the previous measurement, when extracting the $\pi\pi$ scattering lengths $a^{0}_{0}$ and $a^{2}_{0}$. Under the assumption of isospin symmetry and using numerical solutions of the Roy equations, the following values are obtained in the plane ($a^{0}_{0}, a^{2}_{0}): a^{0}_{0}=0.233 \pm 0.016_{stat} \pm 0.007_{syst}, a^{2}_{0}=-0.0471 \pm 0.011_{stat} \pm 0.004_{syst}$. The presence of potentially large isospin effects is also considered and will allow comparison with precise predictions from Chiral Perturbation Theory

Search for direct CP violating charge asymmetries in K±→π±π+π−K^\pm\to\pi^\pm\pi^+\pi^- and K±→π±π0π0K^\pm\to\pi^\pm\pi^0\pi^0 decays

A measurement of the direct CP violating charge asymmetries of the Dalitz plot linear slopes $A_g=(g^+-g^-)/(g^++g^-)$ in $K^\pm\to\pi^\pm\pi^+\pi^-$ and $K^\pm\to\pi^\pm\pi^0\pi^0$ decays by the NA48/2 experiment at CERN SPS is presented. A new technique of asymmetry measurement involving simultaneous $K^+$ and $K^-$ beams and a large data sample collected allowed a result of an unprecedented precision. The charge asymmetries were measured to be $A^c_g=(-1.5\pm2.2)\times10^{-4}$ with $3.11\times 10^9$ $K^{\pm}\to\pi^\pm\pi^+\pi^-$ decays, and $A^n_g=(1.8\pm1.8)\times10^{-4}$ with $9.13\times 10^7$ $K^{\pm}\to\pi^\pm\pi^0\pi^0$ decays. The precision of the results is limited mainly by the size of the data sample.Comment: 29 pages, 9 figures. An updated version accepted by the EPJ

SESSION 4: Weak Processes

- Charged Kaon Decays and Charm Decay