MadGraph5_aMC@NLO

WW production with [QCD]

Asked by Sihyun Jeon

Hi MadGraph team,

I have one question regarding the WW production.
I've been using MGv2.7.0

and tried the below command lines using loop_sm model :
1) p p > w+ w- [QCD]
2) g g > w+ w- [QCD]
where p is defined to be "u u~ d d~ c c~ s s~ g" clearly including the gluon.
The question I had is when I did the display diagrams.

I get a gg > quark-square-loop > w+ w- as in [1] above with 2) but not with 1).
This is confusing to me because to my understanding, p includes g 1) should also have the quark-square-loop diagram.

Is there a reason for this?
Or am I totally making a mistake while generating the WW processes?

Regards,
Sihyun.

[1] https://www.semanticscholar.org/paper/Gluon-induced-WW-background-to-Higgs-boson-searches-Binoth-Ciccolini/d7db54074147975d20fdd1dcb8163d9782da7b38/figure/0

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Sihyun Jeon
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Revision history for this message
Sihyun Jeon (shjeon) said : 		#1

Ah is it just the number of vertices
1) WEIGHTED <= 4 or 5
2) WEIGHTED <= 8
that is not allowing square loop contribution calculations for 1) ?

Revision history for this message
Olivier Mattelaer (olivier-mattelaer) said : 		#2

Hi,

p p > w+ w- [QCD]
is requesting NLO accuracy from p p > w+ w- at tree-level.
if you do
generate p p > w+ w-
you do not have any gluon initial state.

Actually g g > w+ w- is a loop-induced and compare to q q~ > w+ w- this a NNLO contribution.
So this is consistent to NOT include it when you do "p p > w+ w- [QCD]"

When you do

generate g g > w+ w- [QCD]
you should see the following information:
------------------------------------------------------------------------
 No Born diagrams found. Now switching to the loop-induced mode.
 Please cite ref. 'arXiv:1507.00020' when using results from this mode.
------------------------------------------------------------------------

You see that you automatically switch to a special mode since MG5aMC do not find any born diagram.
for p p > w+ w-, we do found such diagram and therefore do not need to pass to that mode.
The two mode of computation (NLO and loop-induced) are mutually exclusive and can not be mixed.

Cheers,

Olivier

Revision history for this message
Sihyun Jeon (shjeon) said : 		#3

Ah I just saw this.

THanks for the answer!

Revision history for this message
Sihyun Jeon (shjeon) said : 		#4

Thanks