MadGraph5_aMC@NLO

Cross-section stability

Asked by SOUAD SEMLALI

Dear Olivier,

I am using MG-v2.9.5 to generate events of some processes at the partonic level. I have a question regarding the stability of pp > tt~gg cross-section, with t t~ decaying semi-leptonically (pp > gg t t~> \mu+ \mu- b b~ gg \vm \vm~).
when the cuts are not applied at the partonic level, the cross-section is supposed to be not stable, and yet it is stable.

All the cuts are set to -1 in the run card :
 \sigma(pp > jjtt~ > mu+ mu- b b~ j j \vm \vm~) = 8x10^17 + 6.5x10^17 pb
 \sigma(pp > ggtt~ > mu+ mu- b b~ j j \vm \vm~ ) = 2.93+0.0091 pb !!

15.0 = bwcutoff;

run.log file associated to a subprocess of pp > ggtt~ > mu+ mu- b b~ j j \vm \vm~:
Particle 3 4 5 6 7 8 9 10
      Et > 20.0 20.0 0.0 0.0 0.0 0.0 0.0 0.0
       E > 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
     Eta < 5.0 5.0 -1.0 -1.0 -1.0 -1.0 -1.0 -1.0
   xqcut: 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
d R # 3 > -0.0 0.4 0.0 0.0 0.0 0.0 0.0 0.0
d R # 4 > -0.0 -0.0 0.0 0.0 0.0 0.0 0.0 0.0
d R # 5 > -0.0 -0.0 -0.0 0.0 0.0 0.0 0.0 0.0
d R # 6 > -0.0 -0.0 -0.0 -0.0 0.0 0.0 0.0 0.0
d R # 7 > -0.0 -0.0 -0.0 -0.0 -0.0 0.0 0.0 0.0
d R # 8 > -0.0 -0.0 -0.0 -0.0 -0.0 -0.0 0.0 0.0
d R # 9 > -0.0 -0.0 -0.0 -0.0 -0.0 -0.0 -0.0 0.0
s min # 3> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 4> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 5> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 6> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 7> 0.0 0.0 0.0 0.0 0.0 22.1 22.1 0.0
s min # 8> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
s min # 9> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 3> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 4> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 5> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 6> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 7> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 8> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 9> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
 No cut BW -1 1
 No cut BW -2 2
 No cut BW -3 3
 No cut BW -4 4

some values are not set to -1, although the cuts are set to -1 at the run card.

run.log file associated to a subprocess of pp > jjtt~ > mu+ mu- b b~ j j \vm \vm~:
Particle 3 4 5 6 7 8 9 10
      Et > -1.0 -1.0 0.0 0.0 0.0 0.0 0.0 0.0
       E > 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
     Eta < -1.0 -1.0 -1.0 -1.0 -1.0 -1.0 -1.0 -1.0
   xqcut: 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
d R # 3 > -0.0 -1.0 0.0 0.0 0.0 0.0 0.0 0.0
d R # 4 > -0.0 -0.0 0.0 0.0 0.0 0.0 0.0 0.0
d R # 5 > -0.0 -0.0 -0.0 0.0 0.0 0.0 0.0 0.0
d R # 6 > -0.0 -0.0 -0.0 -0.0 0.0 0.0 0.0 0.0
d R # 7 > -0.0 -0.0 -0.0 -0.0 -0.0 0.0 0.0 0.0
d R # 8 > -0.0 -0.0 -0.0 -0.0 -0.0 -0.0 0.0 0.0
d R # 9 > -0.0 -0.0 -0.0 -0.0 -0.0 -0.0 -0.0 0.0
s min # 3> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 4> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 5> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 6> 0.0 0.0 0.0 0.0 22.1 0.0 0.0 0.0
s min # 7> 0.0 0.0 0.0 0.0 0.0 22.1 22.1 0.0
s min # 8> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
s min # 9> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 3> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 4> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 5> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 6> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 7> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 8> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
xqcutij # 9> 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0
 No cut BW -1 1
 No cut BW -2 2
 No cut BW -3 3
 No cut BW -4 4

Many thanks for any help or any suggestion to alleviate the confusion.

Best regards
Souad

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

So what do you run?
is it this one?

generate p p > g t t~ > mu+ mu- b b~ g g vm vm~
output
launch
set no_parton_cuts
set ickkw 0

or this one:
generate p p > t t~ g g, t > mu+ vm b , t~ > mu- vm~ b~
output
launch
set no_parton_cuts
set ickkw 0

Also check the value of ickkw, if set to one then you would have cut obviously (even if you do not seem to have those from your log)

From your first log it seems that you have cut on the lepton. I would really need more details (which syntax, optimization, ...) you use to see if I can reproduce when using the above command.
Maybe it can be usefull if you can convert this to a bug report such that you can attach your run_card.dat (This will allow me to see if the issue is not that the default run_card does not hide by default some parameter (in this case the lepton cut) that should be include for this process.

Cheers,

Olivier

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