Author(s):
ATLAS collaboration (2902 authors) ; Aguilar-Saavedra, Juan Antonio ; Amor Dos Santos, Susana Patricia ; Anjos, Nuno ; Araque, Juan Pedro ; Castro, Nuno Filipe ; Conde Muiño, Patricia ; Da Cunha Sargedas De Sousa, Mario Jose ; Fiolhais, Miguel ; Galhardo, Bruno ; Gomes, Agostinho ; Gonçalo, Ricardo ; Jorge, Pedro ; Machado Miguens, Joana ; Maio, Amélia ; Maneira, José ; Oleiro Seabra, Luis Filipe ; Onofre, António ; Pedro, Rute ; Santos, Helena ; Saraiva, João ; Silva, José ; Tavares Delgado, Ademar ; Veloso, Filipe ; Wolters, Helmut
Date: 2018
Origin: Laboratório de Instrumentação e Física Experimental de Partículas
Description
Measurements of longitudinal flow decorrelations are presented for charged particles in the pseudorapidity range $|\eta|<2.4$ using 7 $\mu$b$^{-1}$ and 470 $\mu$b$^{-1}$ of Pb+Pb collisions at $\sqrt{s_{\textrm{NN}}}=2.76$ 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 $\eta$ intervals does not factorise into the product of single-particle coefficients, and this breaking of factorisation, or flow decorrelation, increases linearly with the $\eta$ separation between the intervals. The slopes for this flow decorrelation are found to be larger at 2.76 TeV than 5.02 TeV. Higher-order moments of the correlations are also measured, and the corresponding linear coefficients for the $k^{\textrm{th}}$-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 changing with $\eta$. These two contributions are found to be comparable. The longitudinal flow correlations are also measured between $v_n$ of different order in $n$. The longitudinal fluctuations of $v_2$ and $v_3$ are found to be independent of each other, while the longitudinal fluctuations of $v_4$ and $v_5$ are found to be driven by the nonlinear contribution from $v_2^2$ and $v_2v_3$, respectively.
