Event-shape engineering and heavy-flavour observables in relativistic heavy-ion collisions

Andrea Beraudo,Marco Monteno,Arturo De Pace,Marzia Nardi,Francesco Prino

doi:10.1140/epjc/s10052-019-6996-9

Andrea Beraudo, Marco Monteno + Show 3 more

Open Access

https://doi.org/10.1140/epjc/s10052-019-6996-9

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Abstract

Traditionally, events collected at relativistic heavy-ion colliders are classified according to some centrality estimator (e.g. the number of produced charged particles) related to the initial energy density and volume of the system. In a naive picture the latter are directly related to the impact parameter of the two nuclei, which sets also the initial eccentricity of the system: zero in the case of the most central events and getting larger for more peripheral collisions. A more realistic modelling requires to take into account event-by-event fluctuations, in particular in the nucleon positions within the colliding nuclei: collisions belonging to the same centrality class can give rise to systems with different initial eccentricity and hence different flow harmonics for the final hadron distributions. This issue can be addressed by an event-shape-engineering analysis, consisting in selecting events with the same centrality but different magnitude of the average bulk anisotropic flow and therefore of the initial-state eccentricity. In this paper we present the implementation of this analysis in the POWLANG transport model, providing predictions for the transverse-momentum and angular distributions of charm and beauty hadrons for event-shape selected collisions. In this way it is possible to get information on how the heavy quarks propagating (and hadronizing) in a hot environment respond both to its energy density and to its geometric asymmetry, breaking the perfect correlation between eccentricity and impact parameter which characterizes a modelling of the medium based on smooth average initial conditions.

Highlights

In this way it is possible to get information on how the heavy quarks propagating in a hot environment respond both to its energy density and to its geometric asymmetry, breaking the perfect correlation between eccentricity and impact parameter which characterizes a modelling of the medium based on smooth average initial conditions
Event-shape-engineering studies of particle pT -spectra and flow in relativistic heavy-ion collisions, in which events are organized first in centrality classes and in subsamples of high/low eccentricity, have the potential to provide a richer information on the produced medium, disentangling the effects of the size and density of the fireball from the ones related to its geometric asymmetry
In this paper we decided to focus on what one can learn in principle applying such a strategy to the study of heavy-flavour observables, showing results obtained with our POWLANG transport setup

Summary

Introduction

After modelling the initial state with the Glauber-MC approach described, obtaining an average initial condition for the selected subsample of collisions (with cuts on centrality and eccentricity), heavy quarks are distributed in the transverse plane according to the local density of binary collisions. Their propagation in the medium is studied through the relativistic Langevin equation. For a comprehensive review of transport calculations applied to the study of heavy-flavour observables in relativistic heavyion collisions, emphasizing the various source of systematic uncertainties and the state of the art of the extraction of transport coefficients, see for instance Refs. [12,39,40]

Results

POWLANG

Discussion and perspectives