Measurement of {eta} meson production in {gamma}{gamma} interactions and {Gamma}({eta}-->{gamma}{gamma}) with the KLOE detector

We present a measurement of {eta} meson production in photon-photon interactions produced by electron-positron beams colliding with sqrt{s}=1 GeV. The measurement is done with the KLOE detector at the phi-factory DA{Phi}NE with an integrated luminosity of 0.24 fb^{-1}. The e^+e^- --> e^+e^-{eta} cross section is measured without detecting the outgoing electron and positron, selecting the decays {eta}-->{pi}^+{pi}^-{pi}^0 and {eta}-->{pi}^0{pi}^0{pi}^0. The most relevant background is due to e^+e^- --> {eta}{gamma} when the monochromatic photon escapes detection. The cross section for this process is measured as {sigma}(e^+e^- -->{eta}{gamma}) = (856 pm 8_{stat} pm 16_{syst}) pb. The combined result for the e^+e^- -->e^+e^-{eta} cross section is {sigma}(e^+e^- -->e^+e^-{eta}) = (32.72 pm 1.27_{stat} pm 0.70_{syst}) pb. From this we derive the partial width {Gamma}({eta}-->{gamma}{gamma}) = (520 pm 20_{stat} pm 13_{syst}) eV. This is in agreement with the world average and is the most precise measurement to date.