Min pT cut on top quarks

Asked by Sergei Chekanov

 Hello,

 Thanks for the previous answers. My t tbar production works fine for v2_0_0_beta3.
 I need now to generate ttbar at large pT. For Pythia8, I usually use

PhaseSpace:mHatMin = 500
PhaseSpace:pTHatMin = 500

 to populate pT(top)>600 GeV. Is any equivalent cut on the invariant mass of 2-body system (or some pT cut on a heavy particle or a jet) during the generation ?

best, Sergei

Question information

Language:
English Edit question
Status:
Answered
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Last query:
Last reply:
Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said :
#1

Did you want such cut for a LO or a NLO order run?

Cheers,

Olivier

Revision history for this message
Sergei Chekanov (chekanov) said :
#2

 Hello, Olivier

 I'm trying to generated inclusive ttbar at NLO, so if possible, this cut at the generation step should be for NLO.
 But i suspect, if I set it at LO, it may be rather close to what I want.

 best, Sergei

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said :
#3

I thought that it was possible to do it at LO without touching at the code (just at the run_card) but looks like it is not.

At LO, this is however very simple:
you can edit the file
SubProcesses/setcuts.f
around line 180 you have:
         else if (abs(idup(i,1,1)).ge.maxjetflavor+1 .and. abs(idup(i,1,1)).le.5) then
              is_a_b(i)=.true.
c write(*,*)'bjet:the pdg is ',abs(idup(i,1,1)),' maxflavor=',maxjetflavor
         endif

replace it by (one 5 going to a 6):

         else if (abs(idup(i,1,1)).ge.maxjetflavor+1 .and. abs(idup(i,1,1)).le.6) then
              is_a_b(i)=.true.
c write(*,*)'bjet:the pdg is ',abs(idup(i,1,1)),' maxflavor=',maxjetflavor
         endif

Now all the cut associated to the b-quark in the run_card will also be applied on the top quark.
So you can put in the run_card the following line:
  600 = ptb ! minimum pt for the b

For NLO, you can use the same trick, but since they are no class bjet, you can use the class lepton
in the same file path around line 126, you should have:
         if (idup(i,1).eq.11) is_a_lm(i)=.true. ! e-
         if (idup(i,1).eq.13) is_a_lm(i)=.true. ! mu-
you can add after those lines:
         if (idup(i,1).eq.6) is_a_lm(i)=.true. ! e-
         if (idup(i,1).eq.-6) is_a_lm(i)=.true. ! mu-
Now all the cuts linked to the lepton (in the run_card as well) will be applied on the top quark.

Cheers,

Olivier

Can you help with this problem?

Provide an answer of your own, or ask Sergei Chekanov for more information if necessary.

To post a message you must log in.