Study of Z Boson Pair Production in $e^{+}e^{-}$ Collisions at LEP at $\sqrt{s}$=189 GeV

The pair production of Z bosons is studied using the data collected by the L3 detector at LEP in 1998 in $\rm e^+e^-$ collisions at a centre--of--mass energy of 189\,GeV. All the visible final states are considered and the cross section of this process is measured to be $0.74^{+0.15}_{-0.14}\,{(\rm stat.)}\,{\pm 0.04}\,{(\rm syst.)}\, \mathrm{pb}$. Final states containing b quarks are enhanced by a dedicated selection and their production cross section is found to be $0.18^{+0.09}_{-0.07}\,{(\rm stat.)}\,\pm 0.02\,{\rm (syst.)}\, \mathrm{pb}$. Both results are in agreement with the Standard Model predictions. Limits on anomalous couplings between neutral gauge bosons are derived from these measurements