MadSpin ZeroDivisionError on single top decay at LO

Update: I stripped taus from the production-level process, i.e.,
generate qq bb > emu emu qq tt
add process bb qq > emu emu qq tt

and still get the same problem. I also stripped emus from the process, i.e.,
generate qq bb > ta+ ta- qq tt
add process bb qq > ta+ ta- qq tt

and unsurprisingly get the same "ZeroDivisionError" problem.

Update: The problem is also present if I user the built-in model file, sm-no_b_mass

Hi Richard,

Thanks to have spot this before the release. (I guess that the test suite should have spot it but we never knows for sure).

doing a bzr pull should be enough, but since I'm in the plane right now, I might forget to push right away.
So in case here is the patch:

Enjoy Fermilab,

Olivier

=== modified file 'MadSpin/decay.py'
--- MadSpin/decay.py 2018-01-11 10:40:04 +0000
+++ MadSpin/decay.py 2018-02-05 06:02:32 +0000
@@ -2746,6 +2746,8 @@
             decay_text = ', '.join(decay_text)
             commandline = ''
             for proc in processes:
+ if not proc.strip().startswith(('add','generate')):
+ proc = 'add process %s' % proc
                 commandline += self.get_proc_with_decay(proc, decay_text, mgcmd._curr_model)

             commandline = commandline.replace('add process', 'generate',1)
@@ -2847,7 +2849,10 @@
             #catch line like "define" where no decay need to be added
             if not new_proc.strip():
                 continue
- if not new_proc.startswith(('add', 'generate')):
+ if new_proc.startswith('p '):
+ new_proc = 'add process %s' % new_proc
+ logger.critical("wrongly formatted input for MadSpin. Please report this!")
+ elif not new_proc.startswith(('add', 'generate')):
                 commands.append(new_proc)
                 continue

=== modified file 'tests/unit_tests/madspin/test_madspin.py'
--- tests/unit_tests/madspin/test_madspin.py 2018-01-11 10:40:04 +0000
+++ tests/unit_tests/madspin/test_madspin.py 2018-02-05 06:06:55 +0000
@@ -105,7 +105,11 @@
         out = madspin.decay_all_events.get_proc_with_decay('generate g g > h QED=1 [noborn=QCD]', 'h > b b~', cmd._curr_model)
         self.assertEqual(['add process g g > h QED=1 [sqrvirt=QCD], h > b b~ --no_warning=duplicate;'],
                          [out])
-
+
+ # simple case but failing initial implementation. Handle it now but raising a critical message [mute here]
+ with misc.MuteLogger(['decay'], [60]):
+ out = madspin.decay_all_events.get_proc_with_decay('p p > t t~', 't~ > w- b~ QCD=99, t > w+ b QCD=99', cmd._curr_model)
+ self.assertEqual(['add process p p > t t~, t~ > w- b~ QCD=99, t > w+ b QCD=99 --no_warning=duplicate;'],[out])

         self.assertRaises(Exception, madspin.decay_all_events.get_proc_with_decay, 'generate p p > t t~, (t> w+ b, w+ > e+ ve)')

> On 3 Feb 2018, at 23:17, Richard Ruiz <email address hidden> wrote:
>
> Question #664031 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/664031
>
> Richard Ruiz posted a new comment:
> Update: I stripped taus from the production-level process, i.e.,
> generate qq bb > emu emu qq tt
> add process bb qq > emu emu qq tt
>
> and still get the same problem. I also stripped emus from the process, i.e.,
> generate qq bb > ta+ ta- qq tt
> add process bb qq > ta+ ta- qq tt
>
> and unsurprisingly get the same "ZeroDivisionError" problem.
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Thanks Olivier,

This seemed to do the trick. One more question: I am still getting the following warning:

INFO: Estimating the maximum weight
INFO: *****************************
...
...
INFO: Event 146/150 : 7.9s
INFO:
INFO: Decaying the events...
WARNING: The partial cross section for each subprocess can not be determine. due
    Reason: multiple final state in the same subprocess (and the presence of multiple BR)
    Consequence: the <init> information of the lhe will therefore be incorrect. Please correct it if needed.
INFO: Event nb 1000 1.8s
INFO: Event nb 2000 3s

To reiterate, I am decaying tops to e (massless), mu (massless), and taus (massive), so I am wondering if the difference in W boson BRs, i.e.,
INFO: decay channels for w+ : ( width = 2.026475 GeV )
INFO: BR d1 d2
...
INFO: 1.111203e-01 mu+ vm
INFO: 1.111203e-01 e+ ve
INFO: 1.110379e-01 ta+ vt

Is causing this. Suggestions/thoughts?

Hi Richard,

I'm running this script:

import model sm-no_b_mass
define qq = u c d s u~ c~ d~ s~
define bb = b b~
define tt = t t~
define ell = e+ e- mu+ mu- ta+ ta-
define tt = t t~
define bb = b b~
define ww = w+ w-
define vv = ve ve~ vm vm~ vt vt~
generate qq bb > ta+ ta- qq tt
add process bb qq > ta+ ta- qq tt
output
launch
shower=OFF
madspin=ON
#decay t > w+ b
#decay t~ > w- b~
decay tt > ww bb, ww > ell vv
set mb 1.e-5
#set wt Auto
set run_tag smBkg_pp_tqll_3lX_LO_LHC14
set LHC 14
set nevents 10000
set no_parton_cut
set etal 4
set mmll 8

and do not reproduce this warning.

Do you also have such warning in this model or is it only for your BSM model?
Or do you see some part that I missing in my script compare to yours?

Cheers,

Olivier

Dear Olivier,

I am also getting the similar error [1]. And my madgraph version is 2.6.1.

As I can read from the previous post after adding the path that you have given for 2.6.2 it worked. I also tried to do the same but it seems that there is many diffences in the corresponding files for 2.6.1 and 2.6.2.

Could you please also send me the pathch for the version 2.6.1?

For your information, I am trying to generate the below process using the reweight card.

set group_subprocesses Auto
set ignore_six_quark_processes False
set complex_mass_scheme False
import model SM_LS_LM_LT_UFO
generate p p > w+ w+ j j QED=4 QCD=0 NP=1

Let me know if you need more information.

with regards,
Ram

[1]
INFO: generate matrix element for decay only (1 - > N).
INFO: output standalone_msF /uscms_data/d3/asahmed/Gridpack2017/genproductions/bin/MadGraph5_aMCatNLO/aQGC_WPlepWPhadJJ_EWK_LO_NPle1_mjj100pt10/aQGC_WPlepWPhadJJ_EWK_LO_NPle1_mjj100pt10_gridpack/work/process/madspingrid/decay_me
INFO: Done 3.368
INFO: Compiling code
INFO: detect independant decays
INFO: Done in 7.56426692009s
INFO:
INFO: Estimating the maximum weight
INFO: *
INFO: Probing the first 75 events
INFO: with 400 phase space points
INFO:
INFO: No independent decay for one type of final states -> skip those events for the maximum weight computation
INFO:
INFO: Decaying the events...
INFO: Total number of events written: 0/1000
Command "launch" interrupted with error:
ZeroDivisionError : float division by zero
Please report this bug to developers
       More information is found in 'MS_debug'.

       Please attach this file to your report.

Hi,

We tend to do not provide patch for old version of MG5aMC.
Please update to 2.6.5.

This being said I do not think that your problem is the same as the one reported in the question.
I actually believe that you are responsible here (i.e. that you ask something that is not supported or something like that)
But without any information on what you do, I can not help.

So please check with 2.6.5 if this is already fix or not, and if not create a bug report with the debug file, the model directory and the madspin_card (if not present in the debug file)

Cheers,

Olivier