Measurement of event-plane correlations insNN=2.76TeV lead-lead collisions with the ATLAS detector

Abstract

A measurement of event-plane correlations involving two or three event planes of different order is presented as a function of centrality for 7 μb −1 Pb + Pb collision data at √ s NN = 2.76 TeV, recorded by the ATLAS experiment at the Large Hadron Collider. Fourteen correlators are measured using a standard event-plane method and a scalar-product method, and the latter method is found to give a systematically larger correlation signal. Several different trends in the centrality dependence of these correlators are observed. These trends are not reproduced by predictions based on the Glauber model, which includes only the correlations from the collision geometry in the initial state. Calculations that include the final-state collective dynamics are able to describe qualitatively, and in some cases also quantitatively, the centrality dependence of the measured correlators. These observations suggest that both the fluctuations in the initial geometry and the nonlinear mixing between different harmonics in the final state are important for creating these correlations in momentum space.

Measurements of long-range azimuthal anisotropies and associated Fourier coefficients for pp collisions at s=5.02 and 13 TeV and pAaboud1, Bergeås2, Brenner3 et al. 2017Phys. Rev. CSelf Cite784780View full textAdd to dashboardCite

“…Measurements [70,77] and theoretical analyses [78][79][80][81][82] of the correlations between the Fourier coefficients and event-plane angles of different flow harmonics in Pb + Pb collisions have indicated significant "nonlinearity" resulting from collective expansion such that the response of the medium to an initial elliptic eccentricity can contribute to cos(4φ) modulation of the produced particles. In Pb + Pb collisions, the nonlinear contribution to v 4 is found to dominate over the geometric contribution except for the most central collisions where the initial-state fluctuations have the greatest impact.…”

Measurement of the correlation between flow harmonics of different order in lead-lead collisions at sNN=2.76 TeV with the ATLAS detector

“…(3), c 0 = a 0 4 denotes the linear component of v 4 , and coefficients a 0 , a 1 , and c 1 are weak functions of centrality. The nonlinear contribution from v 2 is responsible for the strong centrality dependence of the correlation between 2 and 4 observed by the ATLAS Collaboration [14] in Pb + Pb collisions. In a similar manner, the v 5 signal comprises a linear component proportional to 5 and a leading nonlinear term involving v 2 and v 3 [23,26]: …”

“…This decomposition of the v 5 signal explains the measured EP correlation involving 2 , 3 , and 5 [14].…”

“…The ellipticity or triangularity in each event is characterized by the so-called "flow vector" calculated from the transverse energy (E T ) deposited in the FCal [14,39],…”

“…Hydrodynamic models are used to understand the space-time evolution of the matter by comparing predictions with the measured azimuthal anisotropy [5][6][7]. The success of these models in describing the anisotropy of particle production in heavy-ion collisions at RHIC and the LHC [8][9][10][11][12][13][14] places significant constraints on the transport properties (such as the ratio of shear viscosity to entropy density) and initial conditions of the produced matter [15][16][17][18][19][20].…”