Measurement of η-meson production in γγ interactions and Γ(η → γγ) with the KLOE detector

Abstract

The work done during my Ph.D. is focused on the analysis of the data taken by the KLOE (K LOng Experiment) detector at the -factory DA NE. The topic of my work is \

physics", i.e. the processes e+e􀀀 ! e+e􀀀

! e+e􀀀X, in which each lepton irradiates a virtual photon and the two photons produce the nal state X. The study of

interactions allows one to explore states with quantum numbers JPC = 0 +; 2 +, and to produce scalar and pseudoscalar mesons in the nal state. In particular I focused on the study of the process e+e􀀀 ! e+e􀀀 , analyzing both the charged and neutral decay channels of the meson, ! + 􀀀 0 and ! 0 0 0, and using the data taken by KLOE at p s = 1 GeV, with an integrated luminosity of 240 pb􀀀1. The choice of studying o -peak data is driven by the need to reduce the background from the decays of the meson, which has mass 1020 MeV. The cross section of the irreducible background e+e􀀀 ! is measured in a dedicated analysis. The cross section of the process e+e􀀀 ! e+e􀀀 is measured separately for the two decay channels, and then combined. Finally, the partial width 􀀀( !

) is extracted, obtaining a result which is in agreement with the PDG average, and represents the most precise measurement to date. The paper \Measurement of meson production in

interactions and 􀀀( !

) with the KLOE detector" has been accepted by JHEP and is available at http://arxiv.org/abs/1211.1845.