Dijet Angular Distributions in Proton-Proton Collisions

Abstract

Dijet angular distributions provide an excellent tool for looking at high transverse momentum parton interactions in order to study both QCD and new physics processes. With the Large Hadron Collider (LHC) recently brought into use, an unprecedented energy regime has opened up. ATLAS is one of the experiments at the LHC. Its high performance calorimeter system providing near hermetic coverage in the pseudorapidity range $|\eta| < 4.9$, enables ATLAS to perform reliable jet measurements. Detailed Monte Carlo studies at $\sqrt{s}$ = 14 TeV, the LHC design collision energy, and at $\sqrt{s}$ = 7 TeV, the collision energy foreseen for the initial years of the LHC operation, clearly show that dijet angular distributions can be used to discriminate the Standard Model from a new physics model describing gravitational scattering and black hole formation in large extra dimensions. When considering only the shape of the distributions, both the theoretical and the experimental uncertainties are predicted to be small in those regions where new physics is expected to show up. The study at $\sqrt{s}$ = 7 TeV indicates that ATLAS is already sensitive to large extra-dimensional gravity mediated effects with 1 pb$^{-1}$ of data. The first measurement of dijet angular distributions at $\sqrt{s}$ = 7 TeV with ATLAS was carried out in two mass bins, using data that were recorded early 2010, corresponding to an integrated luminosity of about 15 nb$^{-1}$. The measurement shows good agreement with QCD predictions and demonstrates that ATLAS is ready to search for new physics in the dijet angular distributions with more data. (Less)