# Evidence for collective multiparticle correlations in $p-Pb$ collisions

CMS Collaboration; Khachatryan, V; Sirunyan, A M; Tumasyan, A; Amsler, C; Canelli, F; Chiochia, V; De Cosa, A; Hinzmann, A; Hreus, T; Kilminster, B; Lange, C; Ngadiuba, J; Pinna, D; Robmann, P; Ronga, F J; Taroni, S; Yang, Y; et al (2015). Evidence for collective multiparticle correlations in $p-Pb$ collisions. Physical Review Letters, 115:012301.

## Abstract

The second-order azimuthal anisotropy Fourier harmonics, v2, are obtained in $p-Pb$ and PbPb collisions over a wide pseudorapidity ($\eta$) range based on correlations among six or more charged particles. The p-Pb data, corresponding to an integrated luminosity of 35  $nb^{−1}$, were collected during the 2013 LHC $p$-Pb run at a nucleon-nucleon center-of-mass energy of $5.02 TeV$ by the CMS experiment. A sample of semiperipheral PbPb collision data at $\sqrt{s_{NN}}$=2.76  TeV, corresponding to an integrated luminosity of $2.5 \mu b^{-1}$ and covering a similar range of particle multiplicities as the $p-Pb$ data, is also analyzed for comparison. The six- and eight-particle cumulant and the Lee-Yang zeros methods are used to extract the $v_2$ coefficients, extending previous studies of two- and four-particle correlations. For both the $p-Pb$ and PbPb systems, the $v_2$ values obtained with correlations among more than four particles are consistent with previously published four-particle results. These data support the interpretation of a collective origin for the previously observed long-range ($\Delta\eta$) correlations in both systems. The ratios of $v_2$ values corresponding to correlations including different numbers of particles are compared to theoretical predictions that assume a hydrodynamic behavior of a p-Pb system dominated by fluctuations in the positions of participant nucleons. These results provide new insights into the multiparticle dynamics of collision systems with a very small overlapping region.

## Abstract

The second-order azimuthal anisotropy Fourier harmonics, v2, are obtained in $p-Pb$ and PbPb collisions over a wide pseudorapidity ($\eta$) range based on correlations among six or more charged particles. The p-Pb data, corresponding to an integrated luminosity of 35  $nb^{−1}$, were collected during the 2013 LHC $p$-Pb run at a nucleon-nucleon center-of-mass energy of $5.02 TeV$ by the CMS experiment. A sample of semiperipheral PbPb collision data at $\sqrt{s_{NN}}$=2.76  TeV, corresponding to an integrated luminosity of $2.5 \mu b^{-1}$ and covering a similar range of particle multiplicities as the $p-Pb$ data, is also analyzed for comparison. The six- and eight-particle cumulant and the Lee-Yang zeros methods are used to extract the $v_2$ coefficients, extending previous studies of two- and four-particle correlations. For both the $p-Pb$ and PbPb systems, the $v_2$ values obtained with correlations among more than four particles are consistent with previously published four-particle results. These data support the interpretation of a collective origin for the previously observed long-range ($\Delta\eta$) correlations in both systems. The ratios of $v_2$ values corresponding to correlations including different numbers of particles are compared to theoretical predictions that assume a hydrodynamic behavior of a p-Pb system dominated by fluctuations in the positions of participant nucleons. These results provide new insights into the multiparticle dynamics of collision systems with a very small overlapping region.

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Item Type: Journal Article, refereed, original work 07 Faculty of Science > Physics Institute 530 Physics English 18 February 2015 17 Feb 2016 14:20 08 Dec 2017 18:17 American Physical Society 0031-9007 https://doi.org/10.1103/PhysRevLett.115.012301 http://arxiv.org/abs/1502.05382v2 (Organisation)