problem in parton showering

Asked by Antara Sarkar

Hi MG5team,

I am trying to generate the following process:

define p = p b b~
generate p p > c c~ a @1
add process p p > c c~ a j @2

And then I do parton showering with Pythia8 and MLM matching with matching upto 1 jet.
And I am encountering a problem in parton showering.

  === Results Summary for run: run_01 tag: tag_1 ===

     Cross-section : 4.893 +- 0.01864 pb
     Nb of events : 10000

INFO: Creating Plots for parton level
INFO: Plots for parton level generated, see /home/physics1/Desktop/tisa/MG5_aMC_v2_7_3/cca_bkg_boosted_13_10l_3/HTML/run_01/plots_parton.html
INFO: End Plots for parton level
INFO: Storing parton level results
INFO: End Parton
reweight -from_cards
decay_events -from_cards
INFO: Running Pythia8 [arXiv:1410.3012]
Splitting .lhe event file for PY8 parallelization...
Submitting Pythia8 jobs...
Pythia8 shower jobs: 1 Idle, 3 Running, 0 Done [2 seconds]
/home/physics1/Desktop/tisa/MG5_aMC_v2_7_3/cca_bkg_boosted_13_10l_3/Events/run_01/PY8_parallelization/split_2/ line 2: 2053 Segmentation fault (core dumped) ./MG5aMC_PY8_interface PY8Card.dat &> PY8_log.txt
WARNING: program /home/physics1/Desktop/tisa/MG5_aMC_v2_7_3/cca_bkg_boosted_13_10l_3/Events/run_01/PY8_parallelization/split_2/ 2 launch ends with non zero status: 139. Stop all computation
Pythia8 shower jobs: 0 Idle, 3 Running, 1 Done [6 seconds]
Pythia8 shower jobs: 0 Idle, 2 Running, 2 Done [6 seconds]
Pythia8 shower jobs: 0 Idle, 0 Running, 4 Done [6 seconds]
Command "generate_events run_01" interrupted with error:
Exception : program /home/physics1/Desktop/tisa/MG5_aMC_v2_7_3/cca_bkg_boosted_13_10l_3/Events/run_01/PY8_parallelization/split_2/ 2 launch ends with non zero status: 139. Stop all computation
Please report this bug on
More information is found in '/home/physics1/Desktop/tisa/MG5_aMC_v2_7_3/cca_bkg_boosted_13_10l_3/run_01_tag_1_debug.log'.
Please attach this file to your report.
INFO: storing files of previous run
INFO: Done

However, no such error is encountered after adding the hard process p p > c a to it.

Could you please me understand what is going wrong in the previous process?


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Olivier Mattelaer (olivier-mattelaer) said :


Mg5aMC 2.7.3 is outdated and not supported anymore.
I guess that version is compatible pythia8.1 and likely 8.2 but certainly not 8.3.
However Pythia8.3 is the recommended version now.

The issue itself seems to be a pythia8 related error so I will not be able to comment on it.

So my best suggestion is to install a newer version of MG5aMC and of pythia8 and retry.
if you still face such type of segmentation fault within pythia8, the best is likely to run pythia8 out of madgraph and then to contact pythia8 author.



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