Hadronic physics at KLOE

Abstract

Abstract. New KLOE results on scalar mesons, γγ physics and η physics are presented.Keywords: Scalar mesons, γγ physics, η meson. PACS: 13.25. Es, 13.25.Jx, 13.66.Bc, 14.40.Aq, 14.40.Cs SCALAR PHYSICSThe structure of the scalars below 1 GeV needs to be further clarified. Several models have been proposed to describe them (e.g. qq, four quarks, KK molecules, etc.). The decay of the scalars into two pseudoscalars (S → PP ′ ) can be used to investigate their nature because the branching ratios and the invariant mass of the two pseudoscalars are sensitive to the scalar structure.For this measurement about 400 pb −1 of KLOE collected data have been used. The analysis has been performed for two different η final states, i.e. η → γγ and η → π + π − π 0 . A kinematic fit has been performed imposing the four momentum conservation, the photon velocity and the invariant masses of both η and π 0 . The ηπ 0 invariant mass distribution has been fitted with the "no-structure" [2] and the "kaon loop"[3] models after background subtraction. The results of the fit are shown in table 1. It is interesting to note that both models give a large coupling of the a 0 (980) with the φ meson, indicating a sizable strange quark content in the a 0 (980). The branching ratio obtained for the two different decay chains are in agreement: BR(φ → ηπ 0 γ) = (7.01 ± 0.10 stat. ± 0.20 syst. ) × 10 −5 for the η → γγ final state and BR(φ → ηπ 0 γ) = (7.12 ± 0.13 stat. ± 0.22 syst. ) × 10 −5 for the η → π + π − π 0 final state. [4]. This decay allegedly proceeds through the intermediateThe kaon pair is produced in a J PC = 0 ++ state, so the two kaons are both K S or K L . We have searched for a final state with a K S K S , with both K S ' decaying to π + π − . This request