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 (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 7TeV. In high multiplicity events, a pronounced structure emerges in the two-dimensional correlation function for particle pairs with intermediate p(T) of 1-3 GeV/c, 2.0 <vertical bar Delta(eta)vertical bar < 4.8 and Delta phi approximate to 0. This is the first observation of such a long-range, near-side feature in two-particle correlation functions in p p or p (p) over bar collisions

Possible multiparticle ridge-like correlations in very high multiplicity proton–proton collisions

“…After the penalty factors which we have enumerated are included, the estimated cross-section for the collision of aligned flux tubes is reduced to a value in the neighborhood of 1 microbarn. This is quite similar to the cross section for events with a trigger of more than 110 charged-particle tracks used in the CMS experimental 'ridge' analysis [1].…”

“…We have suggested that the ridge-like correlation found by the CMS collaboration [1,2] in high-multiplicity events in pp collisions at the LHC could be evidence for the collision of aligned high-intensity flux tubes connecting the valence quarks of the colliding protons. A key property is the correlation of ridge events between positive and negative rapidity.…”

“…To be precise, plots of the two-body correlation in relative azimuthal angle δφ, integrated over relative pseudo-rapidity δη at a fixed range of transverse momentum p ⊥ , exhibit a tendency to peak at δφ 0 [1,2].…”

Flow and correlation phenomena measurements in pp, pPb and PbPb collisions at CMS

“…Amazingly, similar correlations were discovered in 2010 at the LHC in high multiplicity events produced in pp collisions at 7 TeV [2] and, some time later, also in pPb collisions, raising questions about the possible common nature of the systems formed in pp, pA and AA collisions.…”

“…6. The normalized SC (2,3) values are found to be very similar between pPb and PbPb systems at high multiplicities. Taken together with the v n results in Fig.…”