Evidence for collectivity in pp collisions at the LHC

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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.

CMS, Physics, Heavy ion, Ridge, Correlation, pp, TRANSVERSE-MOMENTUM DEPENDENCE, PROTON-PROTON, FLOW, PSEUDORAPIDITY, MULTIPLICITY, Astronomy & Astrophysics, Physics, Nuclear, Physics, Particles & Fields
Khachatryan, V., Sirunyan, A. M., Tumasyan, A., Adam, W., Asilar, E., Bergauer, T., Brandstetter, J., Brondolin, E., Dragicevic, M., Erö, J., Flechl, M., Friedl, M., Frühwirth, R., Ghete, V. M., Hartl, C., Hörmann, N., Hrubec, J., Jeitler, M., König, A., … Woods, N. (2017). Evidence for collectivity in pp collisions at the LHC. In Physics Letters B (Vol. 765, pp. 193–220). Elsevier BV. https://doi.org/10.1016/j.physletb.2016.12.009