CMS-PAS-HIN-15-009

CMS-PAS-HIN-15-009
Azimuthal anisotropy harmonics from long-range correlations in high multiplicity pp collisions at $\sqrt{s} =$ 7 TeV
CMS Collaboration
October 2015

Abstract: Measurements of two- and four-particle angular correlations in pp collisions at $\sqrt{s_{_{NN}}} =$ 7 TeV are presented as a function of charged-particle multiplicities. The data, corresponding to an integrated luminosity of about 6.2 pb $^{-1}$ , were collected during the 2010 LHC pp run using the CMS detector. In high-multiplicity events, a long-range ( $\|\Delta\eta\|>$ 2), near-side ( $\Delta\phi \approx$ 0) structure is found in the two-particle $\Delta\eta$ - $\Delta\phi$ correlation functions. The second-order ( $v_2$ ) and third-order ( $v_3$ ) azimuthal anisotropy harmonics of charged particles, $\text{K}_{\text{S}}^{0}$ and $\Lambda$ / $\overline{\Lambda}$ particles are extracted from long-range two-particle correlations as a function of particle multiplicity and transverse momentum, after correcting for the contribution of back-to-back jet correlations. A $v_2$ and $v_3$ value of about 4% and 1%, averaging over 0.3 $< p_\mathrm{T} <$ 3 GeV/ $c$ , are observed in the high-multiplicity region, and are found to be smaller than values obtained in pPb and PbPb collisions at similar multiplicities. A measurement of four-particle azimuthal correlations is also presented as a function of multiplicity.
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