Abstract
A search for new interactions and resonances produced in LHC proton–proton (pp) collisions at a centre-of-mass energy was performed with the ATLAS detector. Using a dataset with an integrated luminosity of 36 pb− 1, dijet mass and angular distributions were measured up to dijet masses of ∼3.5 TeV and were found to be in good agreement with Standard Model predictions. This analysis sets limits at 95% CL on various models for new physics: an excited quark is excluded for mass between 0.60 and 2.64 TeV, an axigluon hypothesis is excluded for axigluon masses between 0.60 and 2.10 TeV and quantum black holes are excluded in models with six extra space–time dimensions for quantum gravity scales between 0.75 and 3.67 TeV. Production cross section limits as a function of dijet mass are set using a simplified Gaussian signal model to facilitate comparisons with other hypotheses. Analysis of the dijet angular distribution using a novel technique simultaneously employing the dijet mass excludes quark contact interactions with a compositeness scale Λ below 9.5 TeV.
Highlights
Contributions from the production of a new massive particle that decays into a dijet final state, or the rate could be enhanced through a new force that only manifests itself at very large CM energies
Dijet mass and angular distributions have been measured by the ATLAS experiment over a large angular range and spanning dijet masses up to ≈ 3.5 TeV using 36 pb−1 of 7 TeV pp collision data
The angular distributions are in good agreement with Quantum chromodynamics (QCD) predictions and we find no evidence for new phenomena
Summary
This analysis is focused on those pp collisions that produce two high-energy jets recoiling back-to-back in the partonic CM frame to conserve momentum relative to the beamline. In a previous dijet angular distributions analysis [6], a single measure of isotropy based on y∗ intervals was introduced This measure, Fχ , is the fraction of dijets produced centrally versus the total number of observed dijets for a specified dijet mass range. The interval |y∗| < 0.6 defines the central region where we expect to be most sensitive to new physics and corresponds to the angular region χ < 3.32, while |y∗| < 1.7 extends the angular range to χ < 30.0, where QCD processes dominate This new observable, Fχ (mj j ), is defined using the same fine mj j binning used in analysis of the mj j spectrum. These distributions are compared to theoretical predictions processed through a full detector simulation software
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