UC Santa Cruz

Multi-particle cumulants and corresponding Fourier harmonics are measured for azimuthal angle distributions of charged particles in pp$$pp$$ collisions at s$$\sqrt{s}$$ = 5.02 and 13 TeV and in p$$p$$ + Pb collisions at sNN$$\sqrt{s_{_\text {NN}}}$$ = 5.02 TeV, and compared to the results obtained for low-multiplicity Pb+Pb$$\mathrm{Pb}~+~\mathrm{Pb}$$ collisions at sNN$$\sqrt{s_{_\text {NN}}}$$ = 2.76 TeV. These measurements aim to assess the collective nature of particle production. The measurements of multi-particle cumulants confirm the evidence for collective phenomena in p$$p$$ + Pb and low-multiplicity Pb+Pb$$\mathrm{Pb}~+~\mathrm{Pb}$$ collisions. On the other hand, the pp$$pp$$ results for four-particle cumulants do not demonstrate collective behaviour, indicating that they may be biased by contributions from non-flow correlations. A comparison of multi-particle cumulants and derived Fourier harmonics across different collision systems is presented as a function of the charged-particle multiplicity. For a given multiplicity, the measured Fourier harmonics are largest in Pb+Pb$$\mathrm{Pb}~+~\mathrm{Pb}$$, smaller in p$$p$$ + Pb and smallest in pp$$pp$$ collisions. The pp$$pp$$ results show no dependence on the collision energy, nor on the multiplicity.