Investigating collective effects in small collision systems using PYTHIA8 and EPOS4 simulations

Studies have yielded strong evidence that a deconfined state of quarks and gluons, the quark--gluon plasma, is created in heavy-ion collisions. This hot and dense matter exhibits almost zero friction and a strong collective behaviour. An unexpected collective behaviour has also been observed in small collision systems whose origin is still not understood. The second and third order Fourier coefficients are reported from EPOS4 simulations of pp collisions at s=13. 6 TeV. The second and third harmonic two-particle cumulants, denoted as c₂\2\ and c₃\2\, respectively, depend on charged-particle multiplicity and || gap placed to suppress the contribution from few-particle correlations. The c₂\2\ with || gap is positive and decreases with multiplicity, while the c₃\2\ with || gap is negative and increases with multiplicity. The second and third harmonic four-particle cumulants are consistent with zero over almost the entire multiplicity range which is expected for Gaussian fluctuations. The second-order Fourier coefficient of ^, K^, p+, +, K^ 0 ₒ, and ^-+^+ obtained using the scalar product method is mass-ordered, being more pronounced when a large || gap is employed.