Jul 4 – 11, 2018
COEX, SEOUL
Asia/Seoul timezone

Elliptic flow of direct photons in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV from ALICE

Jul 6, 2018, 4:48 PM
18m
105 (COEX, Seoul)

105

COEX, Seoul

Parallel Heavy Ions Heavy Ions

Speaker

Mr Mike Henry Petrus Sas (Nikhef National institute for subatomic physics (NL))

Description

Elliptic flow of direct photons in Pb-Pb collisions at $\sqrt{s_{NN}}=2.76$ TeV from ALICE

Direct photons are produced in all stages of a ultrarelativistic heavy-ion collisions and are sensitive to details of the space-time evolution of the produced medium. The low ${\textit p}_{\rm T}$ part of the direct photon spectrum is expected to be dominated by thermal direct photons - thermal radiation of hot matter, i.e., of the quark-gluon plasma and the hadron gas. At RHIC energies it is a challenge for hydrodynamical models to simultaneously described the yield and the elliptic flow of direct photons which is often referred to as the direct-photon puzzle.

The ALICE detector is equipped with two electromagnetic calorimeters and a central tracking system that make it well suited to study direct photon production at low and intermediate ${\textit p}_{\rm T}$. Photons are also detected via conversions in the ALICE detector material with the $e^{+}e^{-}$ pair reconstructed in the central tracking system.

In this talk the final results on the direct photon elliptic flow ($v_{2}^{\gamma ,dir}$) at $\sqrt{s_{\rm NN}}=2.76$ TeV from the Pb-Pb run in 2010 will be presented for central and semi-central collisions. This is the first time that the direct photon flow is calculated by combining conversion and calorimetric measurements in the ${\textit p}_{\rm T}$ range of $0.9<{\textit p}_{\rm T}<6.2$ GeV/c. Comparisons to PHENIX results and to predictions of several theoretical models will be presented in order to shed light on the direct photon puzzle at LHC energies.

Primary author

Mr Mike Henry Petrus Sas (Nikhef National institute for subatomic physics (NL))

Presentation materials