ZZ production at hadron colliders in NNLO QCD

We report on the first calculation of next-to-next-to-leading order (NNLO) QCD corrections to the inclusive production of Z-boson pairs at hadron colliders. Numerical results are presented for pp collisions with centre-of-mass energy (s) ranging from 7 to 14 TeV. The NNLO corrections increase the NLO result by an amount varying from 11% to 17% as s goes from 7 to 14 TeV. The loop-induced gluon fusion contribution provides about 60% of the total NNLO effect. When going from NLO to NNLO the scale uncertainties do not decrease and remain at the ±3% level.