Image source: © P. Weber, Ph.D. Thesis
Many signals of new physics at the LHC involve hadronic jets. A jet is created from a scattered quark or gluon due to the confinement. It is reconstructed in the calorimeter system. The goal of the jet reconstruction is to obtain the initial parton energy out of the measured jet energy. In this procedure one has to take into account both the detector effects (non-compensating calorimeter, dead regions, passive material, calorimeter noise etc.) and the physics effects (final state radiation, multiple interactions, jet algorithm features etc.). Complicated Monte-Carlo based methods of jet reconstruction and of energy calibration are worked out in ATLAS. However, the final energy scale has to be checked in the data. Our group works on such methods of 'in-situ' jet calibration.
For many physics measurements in ATLAS, precise knowledge of the jet energy scale (JES) and its uncertainty is important. One way to validate the JES correction and to determine the uncertainty, is the jet pseudorapidity intercalibration, which is an in-situ measurement and balances dijet events. We developed a new method to select an increased statistical data sample of dijet events. Contrary to standard in-situ methods in ATLAS, which only utilize fully efficient triggers, this new method, called the Trigger Combination Method (TCM), combines many different, single jet triggers. Each individual trigger is not necessarily fully efficient, but the entire set is. The study includes comparisons of the obtained calorimeter response with the responses obtained from standard methods as well as the responses from Monte Carlo predictions. Furthermore systematic studies have been carried out to estimate the total systematic uncertainty of the TCM method.