4th MEETING WZ inclusive polarisation - 26 March 2020 
  https://indico.in2p3.fr/event/23939/

  Ansgar, Emmanuel, Francesco, Giovanni, Iro, Lucia, Luka

 1. NLO calculations have NLO accuracy only for observables that are inclusive in the additional QCD parton radiation, otherwise LO accuracy.
   Example pTWZ  ( Q/A:  PtWZ obtained in NLO calculation is not 0, but will have a distribution due to the real emission of a parton)

 2. The LO merging approach with 0j +1j samples, approximates the NLO result but misses virtual corrections

 3. Big difference NLO -->LO (large k factors), nevertheless
     good agreement in distributions between MoC@NLO and merged LO samples (MG+0,1jet) at PARTON level  
     --> merged LO samples catch quite well NLO effects. This because virtual corrections (see 2.) are relatively small 

 4. There  is a 1-bin-peak at ~ 25 GeV in the ratio in PTW between MoC@NLO and merged LO samples (MG+0,1jet) at PARTON level. This is due to the   ptJet cut in Madgraph
   in the 1 jets sample. This is expected to be correlated  with the difference in the ratio seen  in pWLZL  at high value in particular for LL.
   To be checked generating Madgraph 0,1 jet lowering the ptJ cut.

 5. For some of the variables (ex: PTW and DNN, in particular pWLZL) worst agreement between MoC@NLO and merged LO samples (MG+0,1jet) at PARTICLE level
      ---> Q: could the PTW effect due to QED FSR radiation ? (this effect is accounted in the parton shower so not present at parton level) 
           A: Yes, but this cannot explain all: ~ the same disagreement when using dressed or Born leptons

 6. Q. To account for 5. above (difference particle/parton), when we reweight to MoCatNlo, should we account for an additional factor for particle to parton correction ?
          (obtained just as ratio particle/Parton)?
                      (N.B: This ratio particle/parton is not the same for "0j sample" and "1j sample").
    A: It may work but not possible to give an uncertainty.
       --> We could check if this factorisation works for an unpolarised sample where we have the NLO result. 
           We could do several things with unpolarised samples: for example compare :
               (parton level)_Powheg (NLO)   REWEIGHTED by (particle/parton)Madgraph at NLO    with Powheg NLO particle level