Evidence of different $\Lambda_{\rm c}$-baryon and D-meson elliptic flow in Pb$-$Pb collisions at $\mathbf{\sqrt{\textit{s}_{\rm NN}}}$ = 5.36 TeV with ALICE at the LHC

TL;DR

This paper measures the azimuthal anisotropy ($v_2$) of charm hadrons in Pb-Pb collisions at 5.36 TeV, revealing differences between baryons and mesons that suggest quark coalescence and partonic collectivity.

Contribution

First measurement of $v_2$ of prompt $ m{ extLambda_c}$ baryons in heavy-ion collisions, showing a larger $v_2$ than D mesons, supporting quark coalescence models.

Findings

$v_2$ of D$^0$ and D$^+$ are similar.

Hint of difference between D$^0$ and D$^+_s$ $v_2$ at low $p_T$.

Larger $v_2$ for $ m{ extLambda_c}$ baryons compared to D mesons.

Abstract

The ALICE collaboration reports the azimuthal-anisotropy coefficient $v_2$ of prompt D$^0$, D$^+$, D$^+_{\rm s}$ mesons and the first measurement of $v_2$ of prompt $\Lambda_{\rm c}$ baryons in semicentral Pb$-$Pb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.36$ TeV. The D mesons and $\Lambda_{\rm c}$ baryons are reconstructed in their hadronic decays at midrapidity ($ |y|<0.8$) in the transverse-momentum interval $0.5< p_{\rm T} < 24$ GeV/$c$. Similar $v_2$ values are measured for D$^0$ and D$^+$, while a hint of a difference ($2.6\sigma$) emerges between D$^0$ and D$^+_{\rm s}$ mesons in the $1 < p_{\rm T} < 5 $ GeV/$c$ interval. A larger $v_2$ for $\Lambda_{\rm c}$ baryons with respect to D$^0$ mesons is observed with $3.7\sigma$ significance for $4 < p_{\rm T} < 12$ GeV/$c$, providing evidence for the partonic origin of charm-hadron $v_2$ and hadron formation via quark coalescence. This interpretation is further supported by comparisons with theoretical calculations of charm-quark transport in a hydrodynamically expanding medium.