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

Abstract

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 7TeV are presented, using data collected with the CMS detector over a broad range of pseudorapidity (η) and azimuthal angle (φ). Short-range correlations in Δη, 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 η (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 7TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate px of 1-3 GeV/c, 2.0 < |Δη| < 4.8 and Δφ ≈0. This is the first observation of such a long-range, near-side feature in two-particle correlation functions in pp or pp̄ collisions.