Before jets can be used in measurements or searches for new physics, a large number of calibrations steps are required, which are based on both Monte Carlo (MC) generated pseudo data and data recorded at the ATLAS detector. After reconstruction, the jets are first calibrated using MC in order to correct for possible effects in the reconstruction. For example, neutrinos can be produced in the hadronic shower that leave the detector without leaving any energy behind, i.e. energy is lost in the reconstruction. Furthermore, hadrons could lie outside the radius of the jet and their energy could also be lost. This is followed by an in situ calibration, in which deviations in the jet energy scale (JES) between the data and MC-generated pseudo data are removed. The JES corrects for effects of the detector, such as losses due to passive detector material, fragmentation and pileup (simultaneous pp collisions) effects.

Various analyses are combined for the in-situ calibration in order to cover a large kinematic range. In the direct-balance method with Z+jets events, a selection is used in which a large-radius jet and a dileptonically decaying Z boson, which is produced in the opposite direction to the jet, are selected. A well-calibrated reference object is constructed from the charged lepton pairs, which is used to calibrate the transverse momentum of the jet, simply using momentum conservation when no further hadronic activity is present

In this project, studies shall be carried out in preparation for the upgrade of the LHC (High-Luminosity LHC), which should serve as validation of the simulation and detector conditions. Furthermore, it will be demonstrated that the method still works at high pileup rates, as many events will contain additional hadronic activity.

Back