Formation of the ηc in two-photon collisions at LEP

The two-photon width Γγγ of the ηc meson has been measured with the L3 detector at LEP. The ηc is studied in the decay modes π+π−π+π−, π+π−K+K−, K0sK±π∓, K+K−π0, π+π−η, π+π−η′, and ρ+ρ− using an integrated luminosity of 140 pb−1 at s≃91 GeV and of 52 pb−1 at s≃183 GeV. The result is Γγγ(ηc)=6.9±1.7stat±0.8sys±2.0(BR) keV. The Q2 dependence of the ηc cross section is studied for Q2<9 GeV2. It is found to be better described by a Vector Meson Dominance model form factor with a J-pole than with a ρ-pole. In addition, a signal of 29±11 events is observed at the χc0 mass. Upper limits for the two-photon widths of the χc0, χc2, and ηc′ are also given.