Measurement of dijet $p_{\mathrm{T}}$ correlations in Pb+Pb and $pp$ collisions at $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV with the ATLAS detector

Measurements of dijets in both Pb+Pb and $pp$ collisions at a nucleon--nucleon centre-of-mass energy of $\sqrt{s_{\mathrm{NN}}}=2.76$ TeV are presented. The measurements were performed with the ATLAS detector at the LHC using data samples with integrated luminosities of 0.14 nb$^{-1}$ and 4.0 pb$^{-1}$ for the Pb+Pb and $pp$ data samples, respectively. Jets were reconstructed using the anti-$k_t$ algorithm with $R=0.4$. A background subtraction procedure was applied to correct the jet kinematics for the large underlying event present in Pb+Pb collisions. Measurements are reported of the normalized yields $\frac{1}{N}\frac{\mathrm{d}N}{\mathrm{d}x_{\mathrm{J}}}$, where $x_{\mathrm{J}}=p_{\mathrm{T}_{2}} / p_{\mathrm{T}_{1}}$ and $ p_{\mathrm{T}_{1}}$ and $p_{\mathrm{T}_{2}}$ are the leading and subleading jet transverse momenta, respectively. The results are presented as a function of $p_{\mathrm{T}_{1}}$ and collision centrality. The results were obtained by measuring the two-dimensional $p_{\mathrm{T}_{1}}-p_{\mathrm{T}_{2}}$ distributions and applying an unfolding procedure to account for experimental resolution in the measurement of both jets' transverse momenta simultaneously. 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 consistent with expectations from partonic energy loss.