Measurement of gamma gamma->taut au and the limint on tau anomalous magnetic
and
electric moment
L3 collaboration
The QED processes e+e-
--> e+e- mu+mu- and e+e- --> e+e- tau+tau- are studied
with the
L3 detector at LEP using an untagged data sample collected
at
centre-of-mass energies 161 GeV < sqrt(s) < 209 GeV. The TAU
-pairs
are
observed through the associated decay of one tau into
e nu nu
and the
other into pi pi nu. The cross sections are measured
as a function of sqrt(s).
For muon pairs, the cross
section of the g g --> mu+mu-
process is also measured
as a
function of the two-photon centre-of-mass energy for 3 GeV
< W(gg) < 40 GeV.
Good agreement is found between these measurements
and the O (alpha^4)
QED expectations. In
addition, limits on the anomalous magnetic
and electric dipole moments of the tau lepton are
extracted.