Measurement of longitudinal flow decorrelations in Pb plus Pb collisions at root s(NN)=2.76 and 5.02 TeV with the ATLAS detector

Abstract

Measurements of longitudinal flow correlations are presented for charged particles in the pseudorapidity range

| η | < 2.4

using 7 and 470

μ

b

- 1

of Pb+Pb collisions at

s NN

= 2.76

and 5.02 TeV, respectively, recorded by the ATLAS detector at the LHC. It is found that the correlation between the harmonic flow coefficients

v n

measured in two separated η intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the η separation between the intervals. The flow decorrelation is stronger at 2.76 TeV than at 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the

k th

-moment of the

v n

are found to be proportional to k for

v 3

, but not for

v 2

. The decorrelation effect is separated into contributions from the magnitude of

v n

and the event-plane orientation, each as a function of η . These two contributions are found to be comparable. The longitudinal flow correlations are also measured between

v n

of different order in n. The decorrelations of

v 2

and

v 3

are found to be independent of each other, while the decorrelations of

v 4

and

v 5

are found to be driven by the nonlinear contribution from

v 2 2

and

v 2

v 3

, respectively.