Investigations of anisotropic flow using multi-particle azimuthal correlations in pp, p-Pb, Xe-Xe, and Pb-Pb collisions at the LHC
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Abstract (data abstract)
We report measurements of anisotropic flow coefficients ($v_n$) and their cross-correlations using two- and multi-particle cumulant methods in collisions of pp at $\sqrt{s} = 13$ TeV, p--Pb at $\sqrt{s_{_{\rm NN}}} = 5.02$ TeV, Xe--Xe at $\sqrt{s_{_{\rm NN}}} = 5.44$ TeV, and Pb--Pb at $\sqrt{s_{_{\rm NN}}} = 5.02$ TeV recorded with the ALICE detector. These measurements are performed as a function of multiplicity in the mid-rapidity region $|\eta|<0.8$ for the transverse momentum range $0.2 < p_{\rm T} < 3.0$ GeV/$c$. An ordering of the coefficients $v_2 > v_3 > v_4$ is found in pp and \pPb\ collisions, similar to that seen in large collision systems, while a weak $v_2$ multiplicity dependence is observed relative to nucleus-nucleus collisions in the same multiplicity range. Using the novel subevent method, $v_{2}$ measured in pp and \pPb\ collisions with four-particle cumulants is found to be compatible with that from six-particle cumulants. We also present the symmetric cumulants $SC(m,n)$ calculated with the subevent method which evaluate the correlation strength between $v_n^2$ and $v_m^2$. The presented data, which add further support to the existence of long-range multi-particle azimuthal correlations in high multiplicity pp and \pPb\ collisions, can neither be described by PYTHIA8 nor by IP-Glasma+MUSIC+UrQMD model calculations, and hence provide new constraints on collective effects in small collision systems.