The reactions $\pi\pi \rightarrow \pi\pi$ π π → π π and $\gamma\gamma \rightarrow \pi\pi$ γ γ → π π in $\chi$ χ PT with an isosinglet scalar resonance

Measurement of Γ ( K S → π + π − ( γ ) ) / Γ ( K S → π 0 π 0 )

We have measured the ratio R S = Γ(KS → π π(γ))/Γ(KS → π π) with the KLOE detector at the DAΦNE ee collider. This measurement is fully inclusive with respect to the ππγ final state. The sample of over 10 two-pion decays of tagged KS mesons allows a statistical error as low as ∼ 0.1% to be obtained. The accuracy is limited by systematic uncertainties, which are estimated primarily from data. We ...

η → π + π − π 0 γ in Chiral Perturbation Theory

0 Observation of the φ → π + π − π + π − Decay

Using 11.6 pb of data collected in the energy range 0.984–1.06 GeV by CMD-2 at VEPP-2M, the cross section of the reaction e+e− → π+π−π+π− has been studied. For the first time an interference pattern was observed in the energy dependence of the cross section near the φ meson. The branching ratio of the φ → π+π−π+π− decay double suppressed by the G-parity and OZI rule is measured Br(φ → ππππ) = (...

Direct CP Violation in KL → π + π − γ

CP violation due to interference between KL and KS decays into π +π−γ is analyzed in the Standard Model. The CP-violating parameter ǫ+−γ , which is the difference between η+−γ and η+−, receives dominant contributions from K 0− K̄ mixing and the gluon penguin diagram; its magnitude is calculated to be 10−2ǫ at a typical region of the Dalitz plot. Genuine direct CP violation in KL → π+π−γ decay or...

Reanalysis of CP Violation in K L → π + π − γ

We present a reanalysis of direct CP violation in the decay K L → π + π − γ. We point out an existing discrepancy between the theoretical and experimental definitions of ǫ ′ +−γ. Adopting the experimental definition of ǫ ′ +−γ , we estimate that ǫ ′ +−γ /ǫ could be as large as a few times 10 −4 both within the standard model and beyond. We discuss these estimates in detail and we also show how ...