Ultralong range angular correlations have been recently reported by the ALICE collaboration in pp collisions at $\sqrt{s}=13\mathrm{TeV}$ below $\mathrm{d}{N}_{\mathrm{ch}}/\mathrm{d}\eta =7$. The measurements have been performed as a function of the charged-particle multiplicity at midrapidity ($N_{\mathrm{ch}}$ in $|\eta |<0.8$), which is known to be strongly sensitive to local multiplicity fluctuations. The present work investigates the impact of the event-activity estimator on ultralong range angular correlations. The study is conducted in the framework of pythia8 with the string shoving mechanism since it gives a nonzero elliptic flow coefficient, $V_{2\mathrm{\Delta }}$. Such collectivelike effects arise from repulsive interactions between overlapping color strings, without invoking hydrodynamic collectivity. The analysis is conducted as a function of $N_{\mathrm{ch}}$, the number of parton-parton scatterings ($N_{\mathrm{mpi}}$) and flattenicity. Surprisingly, for ultralong range correlations, pp collisions with $N_{\mathrm{mpi}}=1$ (dijets) seem to be the most sensitive to string shoving. The effect diminishes with increasing $N_{\mathrm{mpi}}$. While in data, within uncertainties, $V_{2\mathrm{\Delta }}$ exhibits a weak multiplicity dependence; the string shoving mechanism gives a $V_{2\mathrm{\Delta }}$ that decreases with the increase in $N_{\mathrm{ch}}$. The present work therefore supports the picture stating that mechanisms such as string shoving might explain the low multiplicity limit, whereas, hydro becomes relevant in high-multiplicity pp collisions. This work also suggests that flattenicity might be more effective than $N_{\mathrm{ch}}$ to better handle collectivelike effects.

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• Collective flow
• Quantum chromodynamics
• Quark-gluon plasma
• Relativistic heavy-ion collisions