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 ($p_{\mathrm{T}}$) 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 ($p_{\mathrm{T}}^{\mathrm{jet}}$) 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 $p_{\mathrm{T}}$ spectra when (for a given multiplicity class) the leading jet $p_{\mathrm{T}}$ 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.

arXiv comment16 pages, 6 figures. The text was significantly modified and extended. One figure was removed whereas some were slightly modified. References were corrected and updated. The final version of this paper appears in Journal of Physics G (Nuclear and Particle Physics)

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