Measurements of longitudinal flow decorrelations in 5.02 TeV and 13 TeV $pp$ collisions and 5.44 TeV Xe+Xe collisions with the ATLAS detector

This note presents measurements of longitudinal flow decorrelations in 5.02 TeV and 13 TeV $pp$ collisions and 5.44 TeV Xe+Xe collisions with the ATLAS detector. The measurements are performed using the two-particle correlation method with charged-particle tracks within $|\eta| < 2.5$ and clusters within $4.0<|\eta|<4.9$. Due to the larger influence of non-flow effects in small collision systems, template-based subtraction procedures are developed and used in the measurement. The role of these effects is investigated in large systems such as 5.44 TeV Xe+Xe collisions. Flow decorrelations are characterized in terms of the ratio of the correlation coefficients derived from correlations with a large pseudorapidity gap to those with a small pseudorapidity gap, $r_n$, where $n$ is the flow harmonic moment. The results, quantified as the slope of $r_{2}$ as a function of pseudorapidity gap, are reported as a function of charged-particle multiplicity for the $pp$ and Xe+Xe collision systems.