Measurement of double J/psi productions with the CMS detector

We present the measurement of the cross section for the simultaneous production of two J/psi mesons in proton-proton collisions with the CMS detector. The two J/psi mesons are fully reconstructed in the mu$+$mu- decay and the signal yield is extracted with an extended maximum likelihood fit. The differential cross section is measured in bins of the double J/psi invariant mass, the absolute difference in rapidity of the two J/psi mesons, and the transverse momentum of the double J/psi system. The results can provide the inputs for QCD calculations and for the constraints on the contribution of double-parton scattering.