Auto width of a user defined particle

Asked by Aniket Joglekar on 2017-11-27


I have a user defined model where I am trying to automatically calculate the width of a new particle. I have set "Auto" for width of the new particle in the param card and give command ./bin/generate_events.

It starts writing a new param_card.dat , but then comes to new particle width and stops. When I check the card it writes zero for the width of the particle. In the terminal it throws messages that read :

set automatic_html_opening False --no_save
compute_widths 9000006 --precision_channel=0.01 --body_decay=4.0025 --path=/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/Cards/param_card.dat --output=/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/Cards/param_card.dat
Please note that the automatic computation of the width is
    only valid in narrow-width approximation and at tree-level.
INFO: Get two body decay from FeynRules formula
Results written to /data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/Cards/param_card.dat
INFO: get decay diagram for xchi
Vertexlist of this model has not been searched.Automatically run the model.find_vertexlist()
Found 3 stable particles
Command "generate_events " interrupted in sub-command:
"set max_npoint_for_channel 0" with error:
NameError : name 'myGGH' is not defined
Please report this bug on
More information is found in 'MG5_debug'.
Please attach this file to your report.

I found somewhat relevant discussion on the issue at

So my question is whether this is a Feynrules problems like on the link above of something more? Any ideas/hints?

Feynrules version used for model file generation is newer than the one in the link above.


Here is some more info that might be useful:

I see 2 errors in above error messages namely:

1) "set max_npoint_for_channel 0" with error:
2) NameError : name 'myGGH' is not defined

I believe 0 is correct value in the first line as there are mo loops involved in the decay
For the second error I was wondering if something is wrong with gluon fusion. Following is the output of MG5_debug

set group_subprocesses Auto
set ignore_six_quark_processes False
set loop_optimized_output True
set low_mem_multicore_nlo_generation False
set loop_color_flows False
set gauge unitary
set complex_mass_scheme False
set max_npoint_for_channel 0
Traceback (most recent call last):
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 1430, in onecmd
    return self.onecmd_orig(line, **opt)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 1384, in onecmd_orig
    return func(arg, **opt)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 2026, in do_generate_events
    switch_mode = self.ask_run_configuration(mode, args)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 6001, in ask_run_configuration
    self.ask_edit_cards(cards, plot=False, mode='auto')
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 868, in ask_edit_cards
    self.ask, first_cmd=first_cmd)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 930, in ask_edit_card_static
    cards=cards, mode=mode, **opt)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 1117, in ask
    fct=question_instance, fct_timeout=fct_timeout)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 1640, in timed_input
    result = fct(question)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 1996, in __call__
    return self.cmdloop()
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 2160, in cmdloop
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 167, in cmdloop
    stop = self.postcmd(stop, line)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 5246, in postcmd
    self.do_update('dependent', timer=20)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 5290, in do_update
File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 5575, in do_compute_widths
    return self.mother_interface.do_compute_widths(line)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/pp_chi_uds/bin/internal/", line 2110, in do_compute_widths
    cmd.exec_cmd(line, model=opts['model'])
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/madgraph/interface/", line 1457, in exec_cmd
    stop = Cmd.onecmd_orig(current_interface, line, **opt)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/madgraph/interface/", line 1384, in onecmd_orig
    return func(arg, **opt)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/madgraph/interface/", line 334, in do_compute_widths
    return self.cmd.do_compute_widths(self, *args, **opts)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/madgraph/interface/", line 7931, in do_compute_widths
    ), skip_2body=skip_2body, model=decaymodel)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/madgraph/interface/", line 322, in do_decay_diagram
    return self.cmd.do_decay_diagram(self, *args, **opts)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/madgraph/interface/", line 8191, in do_decay_diagram
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/mg5decay/", line 2842, in find_all_channels
    part.find_channels_nextlevel(self, min_br)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/mg5decay/", line 914, in find_channels_nextlevel
    self['apx_decaywidth'] += temp_channel.get_apx_decaywidth(model)
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/mg5decay/", line 4421, in get_apx_decaywidth
    self.get_apx_psarea(model)/ \
  File "/data2/aniket/llp/MG5_aMC_v2_5_5/mg5decay/", line 4094, in get_apx_matrixelement_sq
    lor_value = eval(new_structure % q_dict_lor)
  File "<string>", line 1, in <module>
NameError: name 'myGGH' is not defined
                          MadGraph5_aMC@NLO Options
        complex_mass_scheme : False
                      gauge : unitary
         group_subprocesses : Auto
  ignore_six_quark_processes : False
           loop_color_flows : False
      loop_optimized_output : True
  low_mem_multicore_nlo_generation : False
 max_npoint_for_channel : 0
               stdout_level : 20 (user set)

                         MadEvent Options
.....etc etc

Let me know if more information is required

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Hi Aniket,

I believe that your model contains some Form-Factor defined in fortran.
When this is the case, the model is not compatible with the automatic three-body computation (and therefore with the Auto option which is configured to check if the three body computation is relevant --this is actually that check which is failing--)

You should still be able to compute 2 body computation, if at the time of the question for the edition of the card you type
compute_widths 6 --body_decay=2

Since the error is in the computation of the relevance of the three-body decay, if you force the computation of the three body decay, it might be going trough as well (but I did not check).

If you really want the Auto feature, then you have to modify the model to use a pure python format.



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