  Measurements of the differential cross sections for the production of exactly
four jets in proton-proton collisions are presented as a function of the
transverse momentum pt and pseudorapidity eta, together with the correlations
in azimuthal angle and the pt balance among the jets. The data sample was
collected in 2010 at a center-of-mass energy of 7 TeV with the CMS detector at
the LHC, with an integrated luminosity of 36 inverse picobarns. The cross
section for a final state with a pair of hard jets with pt > 50 GeV and another
pair with pt > 20 GeV within abs(eta) < 4.7 is measured to be sigma = 330 +- 5
(stat.) +- 45 (syst.) nb. It is found that fixed-order matrix element
calculations including parton showers describe the measured differential cross
sections in some regions of phase space only, and that adding contributions
from double parton scattering brings the Monte Carlo predictions closer to the
data.
