Measurement of jet p_T correlations in Pb + Pb and pp collisions at s_NN=2.76 TeVwith the ATLAS detector

Measurements of dijet p_T correlations in Pb+Pb and pp collisions at a nucleon–nucleon centre-of-mass energy of s_NN=2.76 TeV are presented. The measurements are performed with the ATLAS detector at the Large Hadron Collider using Pb+Pb and pp data samples corresponding to integrated luminosities of 0.14 nb⁻¹ and 4.0 pb⁻¹, respectively. Jets are reconstructed using the anti-k_t algorithm with radius parameter values R=0.3 and R=0.4. A background subtraction procedure is applied to correct the jets for the large underlying event present in Pb+Pb collisions. The leading and sub-leading 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 (1/N)dN/dx_J, where x_J=p_T2/p_T1, 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. Similar features are present in both the R=0.3 and R=0.4 results, indicating that the effects of the underlying event are properly accounted for in the measurement. The results are qualitatively consistent with expectations from partonic energy loss models.