The surprisingly transparent sQGP at LHC

We present parameter-free predictions of the nuclear modification factor, image, of high image pions produced in Pb + Pb collisions at image and 5.5 ATeV based on the WHDG/DGLV (radiative + elastic + geometric fluctuation) jet energy loss model. The initial quark gluon plasma (QGP) density at LHC is constrained from a rigorous statistical analysis of PHENIX/RHIC image quenching data at image and the charged particle multiplicity at ALICE/LHC at 2.76 ATeV. Our perturbative QCD tomographic theory predicts significant differences between jet quenching at RHIC and LHC energies, which are qualitatively consistent with the image-dependence and normalization—within the large systematic uncertainty—of the first charged hadron nuclear modification factor, image, data measured by ALICE. However, our constrained prediction of the central to peripheral pion modification, image, for which large systematic uncertainties associated with unmeasured p + p reference data cancel, is found to be over-quenched relative to the charged hadron ALICE image data in the range image. The discrepancy challenges the two most basic jet tomographic assumptions: (1) that the energy loss scales linearly with the initial local comoving QGP density, image, and (2) that image is proportional to the observed global charged particle multiplicity per unit rapidity as a function of image and centrality class, image. Future LHC identified image hadron image data (together with precise p + p, p + Pb, and Z boson and direct photon Pb + Pb control data) are needed to assess if the QGP produced at LHC is indeed less opaque to jets than predicted by constrained extrapolations from RHIC.