Measurement of \eta meson production in \gamma \gamma interactions and \Gamma \left ( \eta ightarrow \gamma \gamma ight ) with the KLOE detector

摘要

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^{-}\rightarrow e^{+}e^{-}\eta cross section is measured without detecting the out-going electron and positron, selecting the decays \eta \rightarrow \pi ^{+}\pi ^{-}\pi ^{0} and \eta \rightarrow \pi ^{0}\pi ^{0}\pi ^{0}. The most relevant background is due to e^{+}e^{-}\rightarrow \eta \gamma when the monochromatic photon escapes detection. The cross section for this process is measured as \sigma \left ( e^{+} e^{-}\rightarrow \eta \gamma \right ) = \left ( 856\pm 8_{stat}\pm 16_{syst} \right )pb. The combined result for the e^{+}e^{-}\rightarrow e^{+}e^{-}\eta cross section is \sigma \left ( e^{+} e^{-}\rightarrow e^{+}e^{-}\eta \right ) = \left ( 32.72 \pm 1.27_{stat}\pm 0.70_{syst} \right )pb. From this we derive the partial width \Gamma \left ( \eta \rightarrow \gamma \gamma \right )=\left ( 520\pm 20_{stat}\pm 13_{syst} \right ) eV. This is in agreement with the world average and is the most precise measurement to date.