Abstract:
Measurements of two- and multi-particle angular correlations in pp collisions at \(\sqrt{s}\) = 5,7, and 13 TeV are presented as a function of charged-particle multiplicity. The data, corresponding to integrated luminosities of 1.0 pb\(^{-1}\) (5 TeV), 6.2 pb\(^{-1}\) (7 TeV), and 0.7 pb\(^{-1}\) (13 TeV), were collected using the CMS detector at the LHC. The second-order (\(v_{2}\)) and third-order (\(v_{3}\)) azimuthal anisotropy harmonics of unidentified charged particles, as well as \(v_{2}\) of \(K_{S}^{0}\) and \(\Lambda / \overline{\Lambda}\) particles, are extracted from long-range two-particle correlations as functions of particle multiplicity and transverse momentum. For high-multiplicity pp events, a mass ordering is observed for the v2 values of charged hadrons (mostly pions), \(K_{S}^{0}\), and \(\Lambda / \overline{\Lambda}\), with lighter particle species exhibiting a stronger azimuthal anisotropy signal below \(p_T \approx 2GeV/c\). For 13 TeV data, the \(v_{2}\) signals are also extracted from four- and six-particle correlations for the first time in pp collisions, with comparable magnitude to those from two-particle correlations. These observations are similar to those seen in pPb and PbPb collisions, and support the interpretation of a collective origin for the observed long-range correlations in high-multiplicity pp collisions.
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