MadGraph5_aMC@NLO

single top production up to NLO

Asked by Winston

Hi experts,
    I generate all single top production modes, including t-channel, s-channel and tw-channel up to NLO.
But when I launch the processes, madgraph encounter errors. it says

 Result for test_MC:
INFO: Passed.
INFO: Result for check_poles:
Error detected in "launch auto "
And in the log file it says:
raise aMCatNLOError('Poles do not cancel, run cannot continue')
aMCatNLOError: Poles do not cancel, run cannot continue

I generate single top produciton through following codes:
import model sm-no_b_mass
define p = g u c d s u~ c~ d~ s~ b b~
define j = p
generate p p > t j [QCD]
add process p p > t~ j [QCD]
add process p p > t b~ j [QCD]
add process p p > t~ b j [QCD]
add process p p > t w- [QCD]
add process p p > t~ w+ [QCD]

How can I fix the problem?
Thank you.
Best regards.
Winston

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

You have issue with the tt~ production occuring in the real.
You have to substract that contribution (or do the computation in four flavor instead of five flavor).
We do not support as built-in feature such type of substraction. But the MadSTR plugin exists for that purpose ((but I have never used it).

Cheers,

Olivier

Revision history for this message
Winston (adampan) said : 		#2

Hi Olivier,
   I am confused why there have t t~ contribution?
Would u mind giving more intructions on generating single top production?
thank you
Winston

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

Hi,

Since you have this process:
 p p > t~ w+ [QCD]
and that you are doing 5 flavor computation this includes (in the real contribution)
p p > t~ w+ b
which contains tt~ resonant production diagram.
This breaks NLO computation.

As said above, I do not know how to use such PLUGIN:
https://code.launchpad.net/~maddevelopers/mg5amcnlo/MadSTRPlugin
it is documented here: https://arxiv.org/abs/1907.04898
with all the documentation in section 5

Cheers,

Olivier

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