Examining the event-shape-dependent modifications to charged-particle transverse momentum spectra and elliptic flow in p -Pb collisions at energies available at the CERN Large Hadron Collider

Abstract

Purported signatures of collective dynamics in small systems like proton-proton (pp) or proton-nucleus (p-A) collisions still lack unambiguous understanding. Despite the qualitative and/or quantitative agreement of the data to hydrodynamic models, it has remained unclear whether the harmonic flows in small systems relate to the common physical picture of hydrodynamic collectivity driven by the initial geometry. In the present work, we aim to address this issue by invoking a novel concept of event shape engineering (ESE), which has been leveraged to get some control of the initial geometry in high-energy heavy-ion collisions. We utilize ESE by constructing a reference flow vector, q 2 that allows to characterize an event based on its ellipticity. Applying this technique on a data set, simulated from a 3 + 1 dimensional viscous hydrodynamic model EPOS3, we study the event-shape dependent modifications to some of the bulk properties, such as inclusive transverse momentum (p T) spectra and p T-differential v 2 for p-Pb collisions at 5.02 TeV. Selecting events on the basis of different magnitudes of reference flow vector q 2 , we observe a hint of event-shape induced modifications of v 2 as a function of p T , but the inclusive p T spectra of charged particles seem to be insensitive to this event-shape selection.

Different Degree of Complexity in Multiparticle Production at the LHC Energies With the Transition From Soft to Hard Processes: Hint of Possible Sources

“…The flux tubes expand and at some stage get fragmented into string segments of quark-antiquark pairs. In the case of high-multiplicity events, due to a large number of elementary parton-parton scatterings, many flux tubes are produced which lead to a highly dense medium of coloured string segments [56]. The string segments in the bulk matter, which do not have enough energy to escape, form a "core" of thermalized partons that undergoes hydrodynamical expansion following a 3 + 1D viscous hydrodynamic evolution followed by usual Cooper-Frye mechanisms of hadronization.…”