Evidence for collective multi-particle correlations in pPb collisions

Khachatryan, V. and Sirunyan, A. M. and Tumasyan, A. and Adam, W. and Bergauer, T. and Filipovic, Nicolas and Bencze, György and Hajdu, Csaba and Hidas, Pál and Horváth, Dezső and Siklér, Ferenc and Veszprémi, Viktor and Vesztergombi, György and Zsigmond, Anna Júlia and Karancsi, János and Molnár, József and Pálinkás, József and Makovec, Alajos and Trócsányi, Zoltán and Ujvári, Balázs and Veres, Gábor (2015) Evidence for collective multi-particle correlations in pPb collisions. PHYSICAL REVIEW LETTERS, 115 (1). ISSN 0031-9007

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Abstract

The second-order azimuthal anisotropy Fourier harmonics, v2, are obtained in pPb and PbPb collisions over a wide pseudorapidity (η) range based on correlations among six or more charged particles. The pPb data, corresponding to an integrated luminosity of 35 nb−1 , were collected during the 2013 LHC pPb run at a nucleonnucleon center-of-mass energy of 5.02 TeV by the CMS experiment. A sample of semiperipheral PbPb collision data at √sNN = 2.76 TeV, corresponding to an integrated luminosity of 2.5 µb −1 and covering a similar range of particle multiplicities as the pPb data, is also analyzed for comparison. The six- and eight-particle cumulant and the Lee-Yang zeros methods are used to extract the v2 coefficients, extending previous studies of two- and four-particle correlations. For both the pPb and PbPb systems, the v2 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 (large ∆η) correlations in both systems. The ratios of v2 values corresponding to correlations including different numbers of particles are compared to theoretical predictions that assume a hydrodynamic behavior of a pPb 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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