MadGraph5_aMC@NLO

Madgraph v3.5.0 & MC@NLO-Delta

Asked by Soumyadip Barman

Dear experts,

I have a couple of questions regarding Madgraph v3.5.0 & MC@NLO-Delta scheme.

1. For the MC@NLO-Delta scheme to work, it is required to use Pythia8.309. But by default "install pythia8" command in the MG shell downloads Pythia8.306. So, what is the turnaround solution to install the correct version of pythia8 to work the MC@NLO-Delta scheme?

2. As far as I know, for the calculation of "Delta" (Sudhakov-like factor), pythia8 libraries are required. So, my question is - is it possible to run the MC@NLO-Delta scheme in two steps? Like in the first step, we keep the pythia8 libraries and make the proper run_card and process_card, and make a gridpack. And then in the next step use the gridpack to hadronize the process with pythia8.

Looking forward to your suggestions.

Thanks,
Soumyadip

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Rikkert Frederix Edit question
Solved by:
Rikkert Frederix
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Rikkert Frederix (frederix) said : 		#1

Dear Soumyadip,

1. You can simply install pythia8.309 anywhere you want and put the path to that pythia8 installation in the configuration.txt file. (Can be found in the input directory of the main MG5_aMC installation, or, in the Cards directory of a process already generated).

2. Sure, that's no problem. However, also for showering the Delta LHE event files, you also need the pythia8.309 installation, since that version has the (debugged) "separate shower starting scale per dipole" feature correctly implemented.

best,
Rikkert

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Soumyadip Barman (soumyadipbarman) said (last edit ): 		#2

Dear Rikkert,

Thanks for your helpful suggestions.

1. Your suggestion worked well. But there is one problem: By default, "install pythia8" also installs "mg5amc_py8_interface". But when I set the path of installed pythia8.309 in the configuaration.txt file, it starts complaining something like this:

    A Pythia8 path is specified via the option 'pythia8_path' but no path for option
    'mg5amc_py8_interface_path' is specified. This means that Pythia8 cannot be used
    leading order simulations with MadEvent.
    Consider installing the MG5_aMC-PY8 interface with the following command:
     MG5_aMC>install mg5amc_py8_interface

$ install mg5amc_py8_interface
fixed the problem.

2. By using the above logic, I have been able to run the scheme in two steps that I was looking for.

3. Just one more question. Let I don't want to use the MCatNLO-Delta, but only want to use the folding - is this the correct method:
False=MCatNLO-Delta
and change the folding as per need (111 or 221, or 441)?

Thanks,
Soumyadip

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Best Rikkert Frederix (frederix) said : 		#3

Dear Soumyadip,

1. The mg5amc_py8_interface is only at Leading Order. It is completely ignored for MC@NLO and MC@NLO-delta runs.

2. Good.

3. Yes. This is correct.

Best,
Rikkert

Revision history for this message
Soumyadip Barman (soumyadipbarman) said : 		#4

Thanks Rikkert Frederix, that solved my question.