  A measurement of the W boson pair production cross section in proton-proton
collisions at sqrt(s) = 8 TeV is presented. The data collected with the CMS
detector at the LHC correspond to an integrated luminosity of 19.4 inverse
femtobarns. The W+W- candidates are selected from events with two charged
leptons, electrons or muons, and large missing transverse energy. The measured
W+W- cross section is 60.1 +/- 0.9 (stat) +/- 3.2 (exp) +/- 3.1 (theo) +/- 1.6
(lum) pb = 60.1 +/- 4.8 pb, consistent with the standard model prediction. The
W+W- cross sections are also measured in two different fiducial phase space
regions. The normalized differential cross section is measured as a function of
kinematic variables of the final-state charged leptons and compared with
several perturbative QCD predictions. Limits on anomalous gauge couplings
associated with dimension-six operators are also given in the framework of an
effective field theory. The corresponding 95% confidence level intervals are
-5.7 < c[WWW]/Lambda^2 < 5.9 TeV^{-2}, -11.4 < c[W]/Lambda^2 < 5.4 TeV^{-2},
-29.2 < c[B]/Lambda^2 < 23.9 TeV^{-2}, in the HISZ basis.
