MadGraph5_aMC@NLO

When does Madgraph work at NLO?

Asked by Jeff Asaf Dror

I would like to better understand what sort of processes are calculable with Madgraph NLO. To this end I've trying to simulate some simple processes but I am finding some confusing results. In particular if I run,

import model loop_sm
generate h > g g [QCD]
output mytest
launch mytest

I get the right results. However, if I run the very similar process,

import model loop_sm
generate h g > g [QCD]
output mytest
launch mytest

(and edit the run_card.dat to remove the PDFs, lpp1=lpp2=0), then I get the error message:

Error detected in "generate_events run_01"
write debug file /home/jeffdror/Downloads/Programs/MG5_aMC_v2_3_3/mytest/run_01_tag_1_debug.log
If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
MadGraph5Error : Failed the initialization of loop-induced matrix element 'PV0_0_1_hg_g' (trying with a maximum of 15 PS points).

What is fundamentally different between these two options?

Question information

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

Hi,

Well
h g > g
can not be described in the S-matrix formalism.
Indeed it is impossible to have conservation of energy impulsion for that process.

Cheers,

Olivier

> On Feb 11, 2016, at 14:17, Jeff Asaf Dror <email address hidden> wrote:
>
> New question #285045 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/285045
>
> I would like to better understand what sort of processes are calculable with Madgraph NLO. To this end I've trying to simulate some simple processes but I am finding some confusing results. In particular if I run,
>
> import model loop_sm
> generate h > g g [QCD]
> output mytest
> launch mytest
>
> I get the right results. However, if I run the very similar process,
>
> import model loop_sm
> generate h g > g [QCD]
> output mytest
> launch mytest
>
> (and edit the run_card.dat to remove the PDFs, lpp1=lpp2=0), then I get the error message:
>
> Error detected in "generate_events run_01"
> write debug file /home/jeffdror/Downloads/Programs/MG5_aMC_v2_3_3/mytest/run_01_tag_1_debug.log
> If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
> MadGraph5Error : Failed the initialization of loop-induced matrix element 'PV0_0_1_hg_g' (trying with a maximum of 15 PS points).
>
> What is fundamentally different between these two options?
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

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

Let me add that this is a LO process and not a NLO process.
The LO process is at loop level already but it is still a LO process

Cheers,

Olivier
> On Feb 11, 2016, at 14:45, MATTELAER O.P.C. <email address hidden> wrote:
>
> Hi,
>
> Well
> h g > g
> can not be described in the S-matrix formalism.
> Indeed it is impossible to have conservation of energy impulsion for that process.
>
> Cheers,
>
> Olivier
>
>
>> On Feb 11, 2016, at 14:17, Jeff Asaf Dror <email address hidden> wrote:
>>
>> New question #285045 on MadGraph5_aMC@NLO:
>> https://answers.launchpad.net/mg5amcnlo/+question/285045
>>
>> I would like to better understand what sort of processes are calculable with Madgraph NLO. To this end I've trying to simulate some simple processes but I am finding some confusing results. In particular if I run,
>>
>> import model loop_sm
>> generate h > g g [QCD]
>> output mytest
>> launch mytest
>>
>> I get the right results. However, if I run the very similar process,
>>
>> import model loop_sm
>> generate h g > g [QCD]
>> output mytest
>> launch mytest
>>
>> (and edit the run_card.dat to remove the PDFs, lpp1=lpp2=0), then I get the error message:
>>
>> Error detected in "generate_events run_01"
>> write debug file /home/jeffdror/Downloads/Programs/MG5_aMC_v2_3_3/mytest/run_01_tag_1_debug.log
>> If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
>> MadGraph5Error : Failed the initialization of loop-induced matrix element 'PV0_0_1_hg_g' (trying with a maximum of 15 PS points).
>>
>> What is fundamentally different between these two options?
>>
>>
>> --
>> You received this question notification because you are an answer
>> contact for MadGraph5_aMC@NLO.
>

Revision history for this message
Jeff Asaf Dror (asafjeffdror) said : 		#3

Of course you are correct. Should have thought about this more carefully... Thanks!

Revision history for this message
Jeff Asaf Dror (asafjeffdror) said : 		#4

Thanks Olivier Mattelaer, that solved my question.