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

The first measurement of longitudinal decorrelations of harmonic flow amplitudes v(n) for n = 2-4 in Xe + Xe collisions at root s(NN) = 5.44 TeV is obtained using 3 mu 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 fmal-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. root s(NN) = 5.02 TcV, 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 collisions.

Automated summary

This study presents the first measurement of longitudinal decorrelations of harmonic flow amplitudes v(n) in Xe + Xe collisions, showing differences in decorrelation patterns between v(2), v(3), and v(4) as well as their relationships with collision centrality and transverse momentum. Comparisons with Pb + Pb collisions reveal distinct characteristics of longitudinal decorrelation signals in Xe + Xe collisions, highlighting the need for further investigation into the differences in magnitudes and trends of decorrelation ratios between different collision systems. The results provide new insights into the effects of the longitudinal structure of the initial state on heavy-ion collisions.