Observation of Long-Range, Near-Side Angular Correlations in Proton-Proton Collisions at the LHC

Results on two-particle angular correlations for charged particles emitted in proton-proton collisions at center-of-mass energies of 0.9, 2.36, and 7 TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity ($\eta$) and azimuthal angle ($\phi$). Short-range correlations in $\Delta\eta$, which are studied in minimum bias events, are characterized using a simple "independent cluster" parametrization in order to quantify their strength (cluster size) and their extent in $\eta$ (cluster decay width). Long-range azimuthal correlations are studied differentially as a function of charged particle multiplicity and particle transverse momentum using a 980 nb$^{-1}$ data set at 7 TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate transverse momentum of 1-3 GeV/c, $2.0 < \vert\Delta\eta\vert < 4.8$ and $\Delta\phi \sim 0$. This is the first observation of such a long-range, near-side feature in two-particle correlation functions in $pp$ or $p\bar{p}$ collisions.