Jet physics at LHC: cross-section measurement and search for new phenomena at $\sqrt{s}$ = 7 TeV with the ATLAS experiment

The Standard Model of particle physics is so far successful in describing the fundamental particles and their interactions through the electromagnetic, weak, and strong force. However, some hints suggest physics beyond the Standard Model. At the Large Hadron Collider protons are brought to collision at high energies. The resulting final-states can be used in order to probe the Standard Model. One possibility is to use highly energetic quarks and gluons, which are observed as jets. Jet measurements can be examined for existence of particles and phenomena predicted by a number of models. Additionally, jets can be used to obtain information about phenomenological components such as the parton density distribution within the proton. This thesis reports on the measurement of inclusive jet and dijet cross-sections using the ATLAS detector at center-of-mass energies of 7 TeV. The data used was recorded in 2011 and corresponds to an integrated luminosity of 4.5 fb−1 . Jets are defined using the anti-kT algorithm with distance parameters R = 0.4 and R = 0.6. The measurement of the inclusive jet cross-section covers the kinematic region 100 GeV ≤ pT < 2 TeV for rapidities of |y| < 3.0. The measurement of the dijet cross-section covers the dijet mass region 260 GeV ≤ m12 < 5 TeV and dijet rapidity separation of y ∗ < 2.5. The measured spectra are corrected for detector effects and are compared with theoretical predictions. The theoretical predictions are consistent with the experimental measurements within the theoretical and experimental uncertainties. The dijet mass spectrum is used for the search of new resonant-like phenomena. The data set used for this purpose was recorded in 2011 and corresponds to an integrated luminosity of 4.8 fb−1 . Jets are reconstructed using the anti-kT algorithm with the distance parameter R = 0.6. The dijet mass region covered is 850 GeV ≤ mjj < 4 TeV. To suppress t-channel processes the dijet rapidity separation is constrained to y ∗ < 0.6. The background is estimated using data-based techniques. The search for local excesses and the calculation of exclusion limits for a number of heavy resonances is performed using statistical tools. No evidence for significant local discrepancies between the measurement and background was found. Therefore exclusion limits were determined. To name an example: Excited quarks with masses below 2.94 TeV were excluded at 95% Credibility Level.