Browsing by Subject "two-particle [correlation function]"

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    Measurement of long-range pseudorapidity correlations and azimuthal harmonics in √sNN=5.02 TeV proton-lead collisions with the ATLAS detector
    (2014) Aad, G; Abbott, B; Abdallah, J; Abdel Khalek, S; Abdinov, O; Aben, R; Abi, B; Abolins, M; AbouZeid, O S; Abramowicz, H; Abreu, H; Abreu, R; Abulaiti, Y; Acharya, B S; Adamczyk, L; Adams, D L; Adelman, J; Adomeit, S; Adye, T; Agatonovic-Jovin, T; Aguilar-Saavedra, J A; Agustoni, M; Ahlen, S P; Ahmadov, F; Aielli, G; Akerstedt, H; Åkesson, T P A; Akimoto, G; Akimov, A V; Alberghi, G L; Albert, J; Albrand, S
    Measurements of two-particle correlation functions and the first five azimuthal harmonics, v 1 to v 5, are presented, using 28 nb − 1 of p+Pb collisions at a nucleon-nucleon center-of-mass energy of √ sNN = 5 .02 TeV measured with the ATLAS detector at the LHC. Significant long-range “ridge-like” correlations are observed for pairs with small relative azimuthal angle (|∆ φ| < π/ 3) and back-to-back pairs (|∆ φ| > 2π/ 3) over the transverse momentum range 0 . 4 < p T < 12 GeV and in different intervals of event activity. The event activity is defined by either the number of reconstructed tracks or the total transverse energy on the Pb-fragmentation side. The azimuthal structure of such long-range correlations is Fourier decomposed to obtain the harmonics v n as a function of p T and event activity. The extracted v n values for n = 2 to 5 decrease with n. The v 2 and v 3 values are found to be positive in the measured p T range. The v 1 is also measured as a function of p T and is observed to change sign around p T ≈ 1 . 5–2.0 GeV and then increase to about 0.1 for p T > 4 GeV. The v 2 ( p T ) , v 3 ( p T ) and v 4 ( p T ) are compared to the v n coefficients in Pb+Pb collisions at √ sNN = 2 .76 TeV with similar event multiplicities. Reasonable agreement is observed after accounting for the difference in the average p T of particles produced in the two collision systems.