Background study for the search for long-lived particles produced in $pp$ collisions at $\sqrt{s}=13 TeV$ that decay to two displaced hadronic jets in the muon spectrometer at the ATLAS detector

In this report the expected background for a 2 MS vertex search was estimated using a data driven method. Main stream data from 2015, 2016, 2017 and 2018 as well as zero bias data recorded by the ATLAS detector at the LHC was used. It was found that less than one event is expected to have two displaced vertices in the muon spectrometer. Plots for dijet MC and late stream data have also been included but not studied extensively. An unexpected asymmetry between the left and right side of the ATLAS detector was found.