The nuclear modification factor $R_{AA}\left(p_T\right)$ for large transverse momentum pion spectra in Pb+Pb collisions at $\sqrt{s}=2.76$ TeV is predicted within the next-to-leading order perturbative QCD parton model. The effect of jet quenching is incorporated through medium-modified fragmentation functions within the higher-twist approach. The jet transport parameter that controls medium modification is proportional to the initial parton density, and the coefficient is fixed by data on the suppression of large-$p_T$ hadron spectra obtained at the BNL Relativistic Heavy Ion Collider. Data on charged hadron multiplicity $d{N}_{\mathrm{ch}}/d\eta =1584\pm 80$ in central Pb+Pb collisions from the ALICE experiment at the CERN Large Hadron Collider are used to constrain the initial parton density both for determining the jet transport parameter and the 3 + 1 dimensional (3 + 1D) ideal hydrodynamic evolution of the bulk matter that is employed for the calculation of $R_{\mathrm{PbPb}}\left(p_T\right)$ for neutral pions.

• Received 23 March 2011

DOI:https://doi.org/10.1103/PhysRevC.84.034902