Observation of long-range, near-side angular correlations in proton-proton collisions at the LHC

TLDR

The analysis used an independent cluster model to quantify short‑range correlations and examined long‑range azimuthal correlations versus multiplicity and transverse momentum in 7 TeV proton‑proton collisions with 980 pb⁻¹ of data. In high‑multiplicity 7 TeV pp collisions, a pronounced long‑range near‑side ridge appears for particle pairs with 1–3 GeV/c transverse momentum, marking the first observation of such a feature in proton‑proton or proton‑antiproton collisions.

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 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 inverse nb 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< |Delta(eta)| <4.8 and Delta(phi) near 0. This is the first observation of such a long-range, near-side feature in two-particle correlation functions in pp or p p-bar collisions.