Observation of J/psi-pair production in pp collisions at root s=7 TeV

The production of J/psi pairs in proton-proton collisions at a centre-of-mass energy of 7 TeV has been observed using an integrated luminosity of 37.5 pb(-1) collected with the LHCb detector. The production cross-section for pairs with both J/psi in the rapidity range 2 < y(J/psi) < 4.5 and transverse momentum p(T)(J/psi) < 10 GeV/c is