Measurement of $\pi^0$-hadron correlations relative to the event plane in semicentral Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV

TL;DR

This study measures $b5^0$-hadron correlations relative to the event plane in semicentral Pb-Pb collisions at 5.02 TeV, revealing potential additional energy-loss mechanisms beyond path-length dependence.

Contribution

First measurement of $b5^0$-hadron correlations relative to the event plane in Pb-Pb collisions at 5.02 TeV, providing new insights into jet quenching and energy loss mechanisms.

Findings

Suppression of associated charged-particle yields near 2 GeV/c out-of-plane.

No significant event-plane dependence observed at >3 GeV/c.

JEWEL model predictions do not match observed modifications.

Abstract

Per-trigger yields of $\pi^0$-hadron correlations were measured in semicentral Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 5.02$ TeV in ALICE at the LHC. The reconstructed $\pi^0 \rightarrow \gamma \gamma$, with a transverse momentum of $11 < p_{\rm T}(\pi^0) < 14$ GeV/$c$, is used as the trigger particle to calculate yields of associated charged particles on the near- and away-side. The photons are reconstructed using the ALICE Electromagnetic Calorimeter, and the charged particles are measured in the ALICE central barrel within a pseudorapidity range of $|\eta|<0.8$. The yields are reported relative to the orientation of the $\pi^0$ with the $2^{\rm nd}$-order event plane, and are background subtracted using the reaction plane fit method. The data give an indication of a suppression of the associated charged-particle yields near $p_{\rm T} \approx 2$ GeV/$c$ when comparing out-of-plane to in-plane trigger particles. At associated charged-particle $p_{\rm T} > 3$ GeV/$c$, no significant event-plane dependence is observed within uncertainties. The results are compared with predictions from the JEWEL model, which implements jet energy loss in an expanding medium. JEWEL predicts no significant modification of either the near- or away-side associated yields, independent of whether medium recoils are included. The observed behavior may indicate the presence of additional energy-loss mechanisms beyond those governed by path-length dependence.