### Speaker

Dr
Dong Jo Kim
(University of Jyväskylä)

### Description

The centrality dependence of nuclear modification factor($R_{AA}$) carries information about the path-length variation of partonic energy loss. However, the inclusive $R_{AA}$ for a given centrality emerges by averaging over different path lengths as the overlap zone of two colliding nuclei has typically a nearly elliptical shape in the transverse plane. The partons traversing the medium in the in-plane direction are expected to lose less energy than out-of-plane, because they, on the average, have shorter path length inside the medium. In this sense, azimuthal dependence of $R_{AA}$ w.r.t. reaction plane offers to get a tighter constraint on the actual path length traversed by the parton in medium.
Recently we published a paper on the charged particle $R_{AA}$[1], showing that the similar suppression as RHIC energy is observed, and moreover a rising trend for increasing $p_{T}$. Another interesting observation is the similarity of $p_{T}$-differential elliptic flow at low $p_{T}$ between at RHIC and the LHC [2]. Since then, we have extended the $p_{T}$ reach for $R_{AA}$ with better precision and elliptic flow measurement up to 20 $GeV/c$ with event plane, which allows us to study the path-length dependence of partonic energy loss with larger kinematic domain.
We present the latest ALICE results from Pb-Pb collisions at $sqrt{s_{NN}$=2.76TeV on charged particle yields with respect to reaction plane angle as a function of centrality and transverse momentum. These results allow for a detailed examination of the influence of geometry in the collision region and of the interplay between collective flow and jet-quenching effects.
[1] ALICE, K. Aamodt et al., Phys. Lett. B696, 30 (2011), 1012.1004.
[2] ALICE Collaboration, K. Aamodt et al., Phys. Rev. Lett. 105, 252301 (2010).

### Primary author

Dr
Dong Jo Kim
(University of Jyväskylä)