  Double-differential dijet cross sections measured in pp collisions at the LHC
with a 7 TeV centre-of-mass energy are presented as functions of dijet mass and
rapidity separation of the two highest-pT jets. These measurements are obtained
using data corresponding to an integrated luminosity of 4.5/fb, recorded by the
ATLAS detector in 2011. The data are corrected for detector effects so that
cross sections are presented at the particle level. Cross sections are measured
up to 5 TeV dijet mass using jets reconstructed with the anti-kt algorithm for
values of the jet radius parameter of 0.4 and 0.6. The cross sections are
compared with next-to-leading-order perturbative QCD calculations by NLOJET++
corrected to account for non-perturbative effects. Comparisons with POWHEG
predictions, using a next-to-leading-order matrix element calculation
interfaced to a parton-shower Monte Carlo simulation, are also shown.
Electroweak effects are accounted for in both cases. The quantitative
comparison of data and theoretical predictions obtained using various
parameterizations of the parton distribution functions is performed using a
frequentist method. An example setting a lower limit on the compositeness scale
for a model of contact interactions is presented, showing that the unfolded
results can be used to constrain contributions to dijet production beyond that
predicted by the Standard Model.
