Measurements of four-particle cumulants c(n)\4\ for n = 1, 2, 3, 4 are presented using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of single harmonics p(v(n)). For the first time, a negative c(1)\4\ is observed. The c(4)\4\ is found to be negative in central collisions but changes sign around 20-25\% centrality. This behavior is consistent with a nonlinear contribution to v(4) that is proportional to v(2)(2). c(2)\4\ and c(3)\4\ are calculated using two reference event classes in order to investigate the influence of volume fluctuations. Over most of the centrality range, c(2)\4\ and c(3)\4\ are found to be negative, while in the ultra-central collisions, c(2)\4\ changes sign and becomes positive, suggesting a deviation from Gaussian behavior in the event-by-event fluctuation of v(2). The magnitudes of the sign change are also found to be dependent of the event class definition .

Flow fluctuations in Pb plus Pb collisions at root s(NN)=5.02 TeV with the ATLAS detector

Aloisio, Alberto;Alviggi, MariaGrazia;Canale, Vincenzo;Della Pietra, Massimo;Merola, Leonardo;Conventi, Francesco;Rossi, Elvira;de Asmundis, Riccardo;Perrella, Sabrina;Cirotto, Francesco;Lavorgna, Marco;Giannini, Antonio;
2019

Abstract

Measurements of four-particle cumulants c(n)\4\ for n = 1, 2, 3, 4 are presented using 470 mu b(-1) of Pb+Pb collisions at root s(NN) = 5.02 TeV with the ATLAS detector at the LHC. These cumulants provide information on the event-by-event fluctuations of single harmonics p(v(n)). For the first time, a negative c(1)\4\ is observed. The c(4)\4\ is found to be negative in central collisions but changes sign around 20-25\% centrality. This behavior is consistent with a nonlinear contribution to v(4) that is proportional to v(2)(2). c(2)\4\ and c(3)\4\ are calculated using two reference event classes in order to investigate the influence of volume fluctuations. Over most of the centrality range, c(2)\4\ and c(3)\4\ are found to be negative, while in the ultra-central collisions, c(2)\4\ changes sign and becomes positive, suggesting a deviation from Gaussian behavior in the event-by-event fluctuation of v(2). The magnitudes of the sign change are also found to be dependent of the event class definition .
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11588/741382
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