Xilin Zhang, Jinfeng Liao
We study the event-by-event hard probe of geometry and fluctuations in the initial condition of heavy ion collisions from RHIC to LHC energies. Results for the dominant harmonic, $v_2$ at high $p_t$ from jet quenching models with varied path-length and matter-density dependences are compared with precise data sets at both RHIC and LHC. We find that too strong a path-length dependence (e.g. cubic) is ruled out by data at LHC, while the model with strong near-$T_c$ enhancement of jet-medium interaction fully describes data. Quantification of azimuthal harmonics $v_n$ (n=1,2,3,4,5,6) of high $p_t$ hadrons are presented for LHC $2.76\rm TeV$ as well as $5.5\rm TeV$ collisions. We also point out that the near-$T_c$ enhancement model naturally expects a less color-opaque medium at LHC.
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http://arxiv.org/abs/1208.6361
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