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 utilise ESE by constructing a reference flow vector, $q_{2}$ that allows to characterise an event based on it's ellipticity. Applying this technique on a data set, simulated from a 3+1D viscous hydrodynamic model EPOS3, we study the event-shape dependent modifications to some of the bulk properties like, 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.
Highlights
Hydrodynamic modeling has remained the most successful description to the properties of the bulk matter produced in the collisions of heavy nuclei at ultrarelativistic energies [1,2]
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
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
Summary
Hydrodynamic modeling has remained the most successful description to the properties of the bulk matter produced in the collisions of heavy nuclei at ultrarelativistic energies [1,2]. To date, the scopes of exploring the fluid dynamical picture in small systems with intrinsically different initial geometries at the CERN Large Hadron Collider (LHC) energies are unlikely Notwithstanding this limitation, the influence of initial geometry on the final state momentum space anisotropy of the produced particles can be examined with an alternative novel technique namely, the event shape engineering (ESE) [23]. In the framework of Glauber-like initial condition followed by the hydrodynamic evolution, the event-by-event fluctuations in the distributions of the initial nuclear matter is manifested as a large spread in the distributions of initial and final state anisotropies [24] This can be eventually exploited to further categorize events into different classes of initial geometry but at comparable multiplicity.
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