Benchmarking the non-flow contributions to the elliptic flow parameter (v ₂) in proton-proton collisions

This manuscript reports on the elliptic flow parameter, v₂, in proton-proton (p-p) collisions using PYTHIA8 event generator simulations. The typical Event Plane ($EP$) method v₂($EP$) as the one used for the real data analysis has been adopted to measure the v₂ of particles composed of different quark flavors, and produced at mid-pseudorapidity |η| ≤ 1 at center-of-mass energy √s = 200 GeV and √s = 13 TeV. The event plane has been constructed using the soft charged particles with transverse momentum (pT < 2 GeV/c) produced in various η ranges. The pseudorapidity gap technique (Δη) between the particle of interest and the soft charged particles contributed to the event plane constructions has been utilized to benchmark the non-flow contributions. The v₂^π^±,π⁰, v₂J/ψ,Υ, K, D, B, and the v₂^γdir show similar pattern dependence on the transverse momentum for the same Δη, at both √s = 200 GeV and √s = 13 TeV. At each center-of-mass energy, the measured v₂ shows obvious dependence on the quark flavor contents where v₂^γdir ≤ v₂J/ψ, Υ, K, D, B ≤ v₂^π^±,π⁰ for similar Δη gap. The measured v₂ shows slightly higher values at smaller √s for particles of similar values of Δη gaps, particularly at small Δη gap. The measured v₂ for all particles shows systematic decreases with increasing the Δη gap as expected from the previous experimental results. Because PYTHIA8 simulations do not incorporate final state interactions, the v₂(EP) values reported here primarily reflect the non-flow contributions and its dependence on the quark contents, pseudorapidity gap as a function on pT at each center of mass-energy. These contributions should be carefully subtracted from the signal in real data analysis that employs the same event plane determination algorithm.