Speaker
Description
Hadrons carrying heavy flavour (charm or beauty quarks) constitute an exceptional probe to study the properties of the Quark-Gluon Plasma (QGP) created in high-energy heavy-ion collisions. Heavy quarks are produced in initial hard parton-scattering processes of the nucleon-nucleon collisions and on short time scales compared to the QGP formation time. Therefore they experience the entire evolution of the medium interacting with its constituents.
The measurement of the nuclear modification factor ($R_{\rm AA}$) of charmed hadrons
allows us to gain insight into the colour-charge and parton-mass dependence of energy loss as well as into possible modifications of hadronization in presence of the medium.
Results from Pb--Pb collisions at $\sqrt{s}_{\rm NN} = 2.76$ TeV indicate that momentum distributions of charmed mesons are modified in Pb--Pb with respect to pp collisions,
owing to quenching of heavy quarks in the hot and dense medium. The D-meson $R_{\rm AA}$ exhibits a suppression of a factor 5-6 for $p_{\rm T}$ $\approx$ 10 GeV/$c$ in central collisions, with a hint of reduced suppression for D$_{\rm s}$ mesons as compared to non-strange D mesons.
Results from Run 2 will allow us to reduce uncertainties and draw firmer conclusions about possible charm recombination at low and intermediate $p_{\rm T}$ and about colour-charge and parton-mass dependence of energy loss.
The measurement of the elliptic flow ($v_2$) provides further insight into the deconfined phase. At low $p_{\rm T}$, D-meson $v_2$ offers the unique opportunity to test whether also charm quarks participate in the collective expansion dynamics and possibly thermalize in the medium. At low and intermediate $p_{\rm T}$, the elliptic flow is also expected to be sensitive to the hadronization mechanism, while at high $p_{\rm T}$, it can constrain the path-length dependence of parton energy loss. During the LHC Run 1, ALICE measured a positive $v_{2}$ for D$^{\rm 0}$, D$^{\rm +}$, D$^{\rm *}$ mesons in Pb--Pb collisions at $\sqrt{s}_{\rm NN} = 2.76$ TeV. The increased statistics of semi-central Pb--Pb events at $\sqrt{s}_{\rm NN} = 5.02$ TeV, obtained with the LHC Run 2, provides access to more precise results for non-strange D-meson $v_{2}$ as well as to the first measurement of the D$_{\rm s}$-meson elliptic flow at LHC energies.
In this talk, the elliptic flow of D mesons in Pb--Pb collisions at $\sqrt{s}_{\rm NN} = 5.02$ TeV will be presented, together with the status of the D-meson $R_{\rm AA}$ at the same energy.
| Preferred Track | Open Heavy Flavors |
|---|---|
| Collaboration | ALICE |
