Lawrence Berkeley National Laboratory

Back-to-back dihadron spectra in high-energy heavy-ion collisions are studied within the next-to-leading order (NLO) perturbative QCD parton model with jet quenching incorporated via modified jet fragmentation functions due to radiative parton energy loss in dense medium. The experimentally observed appearance of back-to-back dihadron sat high p_T is found to originate mainly from jet pairs produced close and tangential to the surface of the dense matter. However, a substantial fraction of observed high p_T dihadrons also comes from jets produced at the center of the medium after losing finite amount of energy. Consequently, the suppression factor of such high-p_T hadron pairs is foundto be more sensitive to the initial gluon density than the single hadron spectra that are dominated by surface emission. A simultaneous chi2-fit to both the single and dihadron spectra can be achieved within an arrow range of the energy loss parameters epsilon_0=1.6-2.1 GeV/fm. Because of the flattening of the initial jet production spectra, high p_T dihadrons at the LHC energy are found to be more robust as probes of the dense medium.