Follow this recipe: https://twiki.cern.ch/twiki/bin/viewauth/CMS/SWGuideHiggsAnalysisCombinedLimit#ROOT6_SLC6_release_CMSSW_7_4_X
then checkout this directory cd HH4b/BumpSearchLimitCode cmsenv python ProduceWorkspacesHH_13TeV.py
creates bunch of datacards in datacards and workspaces quite a few workspaces
normally you can then simply run
combine datacards/CMS_jj_HH_2000_13TeV_CMS_jj_4btag_cat0.txt -M Asymptotic -n HH -m 2000
This would produce a root file:
higgsCombineHH.Asymptotic.mH2000.root
that contains a TTree names:
limits;1
In this TTree the values are:
0 : 2 sigma Up 1 : 1 sigma Up 2 : median 3 : 1 sigma Down 4 : 1 sigma Down 5 : Observed
And obtain a limit in units of 1 fb. So if you have a limit of 5.8594 it means 5.8594 fb. The datacard for the moment is simply based on 4btag category. A bit of work would be required to add both categories. One need to write properly th function MakeDataCard_1Channel in R2JJFitterHH_13TeV.cc
The Signal trees are located in MiniTrees/Signal_HH and background (QCD MC) in MiniTrees/Background_HH_13TeV.