Longitudinal Flow Decorrelations in Xe+Xe Collisions at sNN=5.44 TeV with the ATLAS Detector

Abstract

The first measurement of longitudinal decorrelations of harmonic flow amplitudes v n for n = 2 – 4 in Xe + Xe collisions at √ s N N = 5.44     TeV is obtained using 3     μ b − 1 of data with the ATLAS detector at the LHC. The decorrelation signal for v 3 and v 4 is found to be nearly independent of collision centrality and transverse momentum ( p T ) requirements on final-state particles, but for v 2 a strong centrality and p T dependence is seen. When compared with the results from Pb + Pb collisions at √ s N N = 5.02     TeV , the longitudinal decorrelation signal in midcentral Xe + Xe collisions is found to be larger for v 2 , but smaller for v 3 . Current hydrodynamic models reproduce the ratios of the v n measured in Xe + Xe collisions to those in Pb + Pb collisions but fail to describe the magnitudes and trends of the ratios of longitudinal flow decorrelations between Xe + Xe and Pb + Pb . The results on the system-size dependence provide new insights and an important lever arm to separate effects of the longitudinal structure of the initial state from other early and late time effects in heavy-ion collision