Scalar mesons and δ 0 − δ 2 at KLOE

The KLOE measurements of φ radiative decays and of the ratio Γ(K S → π + π − (γ))/Γ(K S → π 0 π 0) are discussed. The first measurement aims at understanding the real nature of the scalar mesons a 0 and f 0 , whose possible compositions are q ¯ q, qq ¯ q ¯ q, or K ¯ K molecule. The second measurement is related to the estimate of the phase shift difference δ 0 − δ 2. Previous measurements were affected by a large uncertainty due to the presence of radiative effects which are correctly included in our analysis. 1 The KLOE experiment The KLOE experiment collects data at DAΦNE, an e + e −-collider with center of mass energy ∼ 1020 MeV corresponding to the φ meson mass. The detector consists of a large drift chamber surrounded by an electromagnetic calorimeter, both embedded in a magnetic field of ∼ 0.5 Tesla (Fig. 1). The drift chamber [ 1] is a cylinder 4 m in diameter and 3.3 m in length, with a stereo write-geometry for the reconstruction of the longitudinal coordinate. The momentum resolution for particles with p ≥ 100 MeV is σ p /p ≤ 0.5%. The calorimeter [ 2] is a lead/scintillating-fiber sampling calorimeter, composed of a barrel and two end-caps.