  ATLAS has developed a new approach for vertex selection in VBF invisible
events at HL-LHC conditions, exploiting its new forward tracking capabilities,
integrating calorimeter and tracking information to mitigate the impact of
pileup vertex merging, and introducing a new way to apply pile-up jet
suppression methods for the selection of VBF jets. The new algorithm is
insensitive to pileup density and improves the average vertex selection
efficiency from 86% to 95% under tight VBF event selection cuts.
