The two-photon width Îγγâ of the ηcâ meson has been
measured with the L3 detector at LEP. The ηcâ is studied in the decay
modes Ï+ÏâÏ+Ïâ, Ï+ÏâK+Kâ, Ks0âK±Ïâ,
K+KâÏ0, Ï+Ïâη, Ï+ÏâηâČ, and Ï+Ïâ
using an integrated luminosity of 140 pbâ1 at sââ91 GeV and
of 52 pbâ1 at sââ183 GeV. The result is
Îγγâ(ηcâ)=6.9±1.7(stat.)±0.8(sys.)±2.0(BR) keV. The Q2 dependence of the ηcâ 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 Ï-pole. In addition,
a signal of 29±11 events is observed at the Ïcâ0 mass. Upper limits
for the two-photon widths of the Ïcâ0, Ïcâ2, and ηcâČâ are also
given