Revealing the source of the radial flow patterns in proton--proton collisions using hard probes

Abstract

In this work, we propose a tool to reveal the origin of the collective-like phenomena observed in proton--proton collisions. We exploit the fundamental difference between the underlying mechanisms, color reconnection (CR) and hydrodynamics, which produce radial flow patterns in \textsc{Pythia}~8 and \textsc{Epos}~3, respectively. Specifically, we proceed by examining the strength of the coupling between the soft and hard components which, by construction, is larger in \textsc{Pythia}~8 than in \textsc{Epos}~3. We study the transverse momentum ($p_{\rm T}$) distributions of charged pions, kaons and (anti)protons in inelastic pp collisions at $\sqrt{s}=$ 7\,TeV produced at mid-rapidity. Specific selections are made on an event-by-event basis as a function of the charged particle multiplicity and the transverse momentum of the leading jet ($p_{\rm T}^{\rm jet}$) reconstructed using the \textsc{FastJet} algorithm at mid-pseudorapidity ($|\eta|<1$). From our studies, quantitative and qualitative differences between \textsc{Pythia}~8 and \textsc{Epos}~3 are found in the $p_{\rm T}$ spectra when (for a given multiplicity class) the leading jet $p_{\rm T}$ is increased. In addition, we show that for low-multiplicity events the presence of jets can produce radial flow-like behavior. Motivated by our findings, we propose to perform a similar analysis using experimental data from RHIC and LHC.