UC Berkeley

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 T 1 and p T 2 . An unfolding procedure is applied to the two-dimensional ( p T 1 , p T 2 ) distributions to account for experimental effects in the measurement of both jets. Distributions of ( 1 / N ) d N / d x J , where x J = p T 2 / p T 1 , are presented as a function of p T 1 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.