Vector Boson Scattering (VBS) processes have been a great source of interest for the insight they can give on the EWSB mechanism, as well as for their potential to search for new physics. They are studied at the LHC through the electroweak production of pairs of vector bosons associated to two hadronic jets (VVjj).The large p-p collision datasets from Run2, at a CoM energy of \sqrt{s}=13~TeV, collected by the ATLAS and CMS experiments allowed their first observation, and opened the way to the in-depth study of their properties. The first part of this seminar illustrates some of the interests and challenges of VBS studies, with an emphasis on the case of ATLAS's electroweak WZjj observation.
In order to collect enough data to study such rare processes, dense proton bunches are crossed at the center of the experiments at a rate of 40 MHz. Consequently, a large number of p-p collisions can occur simultaneously (pileup), mostly adding undesired hadronic activity (pileup jets) to the events. In the central regions of the detectors, pileup can be mitigated efficiently with the help of the available tracking information. However, outside the trackers acceptance, only coarse calorimetric information is available, making it harder to tell pileup jets apart from jets linked to the process of interest. The methods developed in ATLAS to handle this problematic, and properly identify forward pileup jets, are discussed in the second part of the seminar
