  Measurements of charged dihadron angular correlations are presented in
proton-proton (pp) and Lead-Lead (PbPb) collisions, over a broad range of
pseudorapidity and azimuthal angle, using the CMS detector at the LHC. In very
high multiplicity pp events at center-of-mass energy of 7 TeV, a striking
"ridge"-like structure emerges in the two-dimensional correlation function for
particle pairs with intermediate pt of 1-3 GeVc, in the kinematic region
2.0<|\Delta\eta|<4.8 and small \Delta\phi, which is similar to observations in
heavy-ion collisions. Studies of this new effect as a function of particle
transverse momentum are discussed. The long-range and short-range dihadron
correlations are also studied in PbPb collision at a nucleon-nucleon
center-of-mass energy of 2.76 TeV, as a function of transverse momentum and
collision centrality. A Fourier analysis of the long-range dihadron
correlations is presented and discussed in the context of CMS measurements of
higher order flow coefficients.
