Event shape engineering with ALICE

TL;DR

This paper demonstrates how event shape engineering in heavy-ion collisions allows for the selection of events with specific initial geometries, significantly affecting the measured elliptic flow coefficient $v_2$ across different centralities and particle types.

Contribution

It introduces the application of event shape engineering in Pb-Pb collisions at 2.76 TeV to control initial geometry effects on flow measurements.

Findings

Event shape engineering effectively selects events with specific initial geometries.

Measured $v_2$ varies significantly for shape-engineered events compared to average.

The method allows for detailed studies of initial state effects on flow.

Abstract

The strong fluctuations in the initial energy density of heavy-ion collisions allow an efficient selection of events corresponding to a specific initial geometry. For such "shape engineered events", the elliptic flow coefficient, $v_2$, of unidentified charged particles, pions and (anti-)protons in Pb-Pb collisions at $\snn = 2.76$ TeV is measured by the ALICE collaboration. $v_2$ obtained with the event plane method at mid-rapidity, $|\eta|<0.8$, is reported for different collision centralities as a function of transverse momentum, $\pt$, out to $\pt=20$ GeV/$c$. The measured $v_2$ for the shape engineered events is significantly larger or smaller than the average which demonstrates the ability to experimentally select events with the desired shape of the initial spatial asymmetry.