Unexpected behavior after cut in generation of p p > t w z
Hello,
I am using MG5_aMC_v2_8_3_2 to generate events of p p > t w z at NLO. This process is interested by overlap with the resonant p p > t t~ z, so I use the MadSTR plugin to remove it, using either DR and DR with interference.
Since the DR scheme doesn't work really well at high pt, and I need to generate events in that spectrum, I also require a cut in pt on b quarks in the final state, to furthermore reduce the overlap; I only want to keep the soft b quarks which have pt < 30 GeV.
To do that, I apply this cut in SubProcesses/cuts.f :
do i=1,nexternal ! loop over all external particles
if (istatus(i).eq.1) then ! final state particle
if ( abs(ipdg(i)).eq.5) then ! bottom quark
c$$$C apply the pT cut (pT should be less than 30 GeV for the event to
c$$$C pass cuts)
if ( p(1,i)**2+p(2,i)**2 .gt. 30d0**2 ) then
c$$$C momenta do not pass cuts. Set passcuts_user to false and return
endif
endif
enddo
These are my generation commands in MadSTR:
import model sm-no_b_mass
generate p p > t w- z [QCD]
add process p p > t~ w+ z [QCD]
My problem is that the cut is not really applied, as I have the majority of events with b quarks over the pt threshold, when I look at the pt distributions from the LHE file.
Moreover, I also plotted the distribution of the b quark pt in three cases:
the cut applied to retain the events with b quark pt < 30 GeV (b-veto)
the cut applied to retain the events with b quark pt > 30 GeV (reversed b-veto)
no cut applied (no veto)
What I see is that the reversed b-veto does exactly what it is supposed to do: I have no events with pt < 30 GeV and then I have a fast decrease after 30.
The no veto category has a flat spectrum.
The b-veto category has the same distribution of the no-veto for pt < 30 GeV and then it is very similar to the reversed b-veto for pt > 30 GeV, where there should be no events whatsoever.
Is this behavior correct or am I neglecting something?
Thank you very much for your help
Question information
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- Assignee:
- marco zaro Edit question
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