Measurement of [eta] meson production in [gamma][gamma] interactions and [Gamma]([eta] [arrow right] [gamma][gamma]) with the KLOE detector

Abstract

(ProQuest: ... denotes formulae and/or non-USASCII text omitted; see image)

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