I am reading a paper from the ATLAS experiment on the identification of tau jets from background jets and came across this figure:
I am struggling to find what the formula is for the inverse background efficiency. Can someone explain to me how this is calculated?
Here is the link to the whole paper: http://cdsweb.cern.ch/record/2064383/files/ATL-PHYS-PUB-2015-045.pdf
Thanks