Recent jet quenching measurements in Pb+Pb collisions at the LHC report a significant energy imbalance of dijets. The imbalance is found to be compensated by a large amount of soft particles produced at large angles with respect to the dijet axis. This observation questions the conventional picture of parton energy loss models, established at RHIC, which typically expect that the radiated gluons are emitted at moderate angles close to the outgoing parton. In this letter, we qualitatively discuss two possible contributions of the underlying heavy-ion background that may have to be taken into account when interpreting the recent data. We show that a large jet $v_3$, potentially caused by a path-length-dependent energy loss in the presence of fluctuating initial conditions, could contribute to the observed excess of soft particles apparently originating from large angle in-medium radiation. In addition, the observed excess could also be induced by multiple jets produced in the vicinity of the leading jet, caused by a potential selection bias imposed on the dijet momentum imbalance.

• Received 13 December 2011

DOI:https://doi.org/10.1103/PhysRevC.85.044916