Measurement of prompt JPSI pair production in pp collisions at sqrt{s}= 7 TeV

Production of prompt J/psi meson pairs in proton-proton collisions at sqrt(s)
= 7 TeV is measured with the CMS experiment at the LHC in a data sample
corresponding to an integrated luminosity of about 4.7 inverse femtobarns. The
two J/psi mesons are fully reconstructed via their decays into muon pairs. This
observation provides for the first time access to the high-transverse-momentum
region of J/psi pair production where model predictions are not yet
established. The total and differential cross sections are measured in a phase
space defined by the individual J/psi transverse momentum pt[J/psi] and
rapidity abs(y[J/psi]): abs(y[J/psi]) < 1.2 for pt[J/psi] > 6.5 GeV; 1.2 <
abs(y[J/psi]) < 1.43 for a pt threshold that scales linearly with abs(y[J/psi])
from 6.5 to 4.5 GeV; and 1.43 < abs(y[J/psi]) < 2.2 for pt[J/psi] > 4.5 GeV.
The total cross section, assuming unpolarized prompt J/psi pair production is
1.49 +/- 0.07 (stat.) +/- 0.13 (syst.) nb. Different assumptions about the
J/psi polarization imply modifications to the cross section ranging from -31%
to +27%.