Pseudorapidity dependence of long-range two-particle correlations in pPb collisions with CMS

CMS measurements of two-particle correlations of charged particles have previously been published for proton-proton (pp), proton-lead (pPb), and lead-lead (PbPb) systems. This paper studies how the two-particle correlations depend on the relative pseudorapidity of the trigger and associate particles ($\Delta\eta$) utilizing a narrow $\eta$ range for the trigger particle. The data were collected during the 2013 pPb run at a nucleon-nucleon center-of-mass energy of 5.02 TeV. The near-side ($\Delta\phi\approx 0$) jet-like correlation is assumed to be of a generalized Gaussian shape in $\Delta\eta$, and fitted with a pedestal long-range pseudorapidity correlation (ridge) in high-multiplicity collisions. The latter is modeled by combinatorial background multiplied by a linear function in $\Delta\eta$, which is found to describe the data well. The jet correlations are subtracted, and the remaining ridge correlations are studied versus $\Delta\eta$ for small seperation in relative azimuthal angle. Furthermore, the Fourier coefficients of the two-particle correlations are extracted for high-multiplicity collisions, with and without subtraction of jet contributions approximated by the scaled low-multiplicity collision data. The $\eta$ dependence of the azimuthal anisotropy parameters is reported.