Dijet asymmetries in Pb+Pb and pp collisions with the ATLAS detector

Measurements of dijet p_T correlations in both Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of $\sqrt{s_{NN}}$ = 2.76 TeV are presented. The measurements were performed with the ATLAS detector at the Large Hadron Collider (LHC) using Pb+Pb and pp data samples with integrated luminosities of 0.14 nb⁻¹ and 4.0 pb⁻¹, respectively. Jets were reconstructed using the anti-k_t algorithm with R = 0.4. A background subtraction procedure was applied to correct the jets for the large underlying event present in Pb+Pb collisions. The leading and subleading jet transverse momenta are denoted p_T1 and p_T2. An unfolding procedure is applied to the two-dimensional p_T1-p_T2 distributions to account for experimental effects in the measurement of both jets. Distributions of $\frac{1}{N}\frac{dN}{d{x}_J}$, where $x_J=\frac{p_{T_2}}{p_{T_1}}$, are presented as a function of p_T1 and collision centrality. The distributions are found to be similar in peripheral Pb+Pb collisions and pp collisions, but highly modified in central Pb+Pb collisions. The results are qualitatively consistent with expectations from partonic energy loss. (paper)