Observation of near-side angular correlations in pPb collisions at 5.02TeV with CMS

The first measurement of two-particle correlations in pPb collisions at a center-of-mass energy of 5.02 TeV is presented. The correlations are studied in azimuth, $\phi$ , and pseudorapidity, $\eta$ , as a function of charged particle transverse momentum, $p_{\rm{T}}$ , and multiplicity. A total of two million collisions are used in this analysis. A long range ($2 < \lvert\Delta\eta\rvert < 4$), near-side ($\Delta\phi \approx 0$) ridge-like structure emerges in the two-particle $\Delta\eta - \Delta\phi$ correlation functions of high multiplicity events. This is the first time such a correlation has been seen in proton-nucleus collisions, which resembles a similar correlation seen in a broad range of nucleus-nucleus collisions and in high multiplicity proton-proton collisions at $\sqrt{s} = 7$ TeV. The correlation strength rises approximately linearly with multiplicity and has a maximum in the range of $p_{\rm{T}} = 1-1.5$ $\rm{GeV}/c$ .