Caterina Bloise (Istituto Nazionale Fisica Nucleare (IT)) Caterina Bloise (Laboratori Nazionali di Frascati (LNF))
The V-->Pgamma Dalitz decays, associated to internal conversion of the photon into a lepton pair, are not well described by the Vector Meson Dominance (VMD) models, as in the case of the process omega --> pi0 mu+ mu-, measured by the NA60 collaboration. The only existing data on phi --> eta e+ e- come from the SND experiment, which has measured the Mee invariant mass distribution on the basis of 213 events. At KLOE, a detailed study of this decay has been performed using both eta-->pi+pi-pi0 and eta-->pi0pi0pi0 final states. Simple analysis cuts provide clean signal events (about 14000 and 30000, respectively), with a residual background contamination of 2-3%. We have also studied the decay phi --> pi0 e+ e-, where no data are available on transition form factor. Dedicated analysis cuts strongly reduce the main background component of Bhabha events to ~20%, leading to ~4000 signal events in the whole KLOE data set. The gamma-gamma couplings and partial widths of mesons provide information about their structure and can be measured in the e+e- --> e+e-gamma*gamma* --> e+e-X processes. The study of gamma*gamma* --> eta will be discussed. The data sample consists of an integrated luminosity of 240 pb-1 of data taken at the center of mass energy SQRT(s)=1 GeV - where backgrounds from phi decays are suppressed - without tagging of the e+e- in the final state. The measurement of the cross section for the reaction gamma*gamma* --> eta in the two decay channels eta-->pi+pi-pi0 and eta-->3pi0, with independent systematic uncertainties, together with the extraction of the eta-->gammagamma width, will be presented.
Fabio Bossi (Laboratori Nazionali di Frascati (LNF))