MadGraph5_aMC@NLO

Pathological behaviour of stop decay

Bug #1649834 reported by Ivan Mikulec on 2016-12-14

This bug affects 1 person

Affects		Status	Importance	Assigned to	Milestone
	MadGraph5_aMC@NLO	Fix Released	Undecided	Unassigned

Bug Description

When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-

a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
10 0 0.3811600E+18 0.4684444E+03 0.7816531E-02 0.1031579E+00
      21 -1 0 0 503 502 0.00000000000E+00 0.00000000000E+00 0.35396361746E+03 0.35396361746E+03 0.00000000000E+00 0. -1.
      21 -1 0 0 504 503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03 0.53577878135E+03 0.00000000000E+00 0. -1.
1000006 2 1 2 504 0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03 0.52848713534E+03 0.42764970339E+03 0. 0.
1000006 2 3 3 501 0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03 0.41652361491E+03 0.30000000000E+03 0. 0.
-1000006 2 1 2 0 502 0.14922534112E+03 0.11953115858E+03 0.62844769711E+02 0.36125526347E+03 0.30000000000E+03 0. 0.
       6 1 4 4 501 0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03 0.24718399018E+03 0.17500000000E+03 0. -1.
1000022 1 4 4 0 0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02 0.16933962473E+03 0.10000000000E+03 0. 1.
      -6 1 5 5 0 502 0.11330615545E+03 0.13433345929E+03 0.52233287346E+02 0.25345034909E+03 0.17500000000E+03 0. -1.
1000022 1 5 5 0 0 0.35919185669E+02 -0.14802300712E+02 0.10611482366E+02 0.10780491438E+03 0.10000000000E+03 0. 1.
      21 1 3 3 504 501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02 0.11196352043E+03 0.00000000000E+00 0. -1.

The stop decay width is set to be very narrow. Please, note also that this happens only to stops and not to anti-stops. This type of events are absent if we do not ask for the stop to decay. We tested this up to the MG version 2.4.2. The cards we used in this example are attached. To us this looks like a bug but we would like to ask you for an opinion.

Revision history for this message

Ivan Mikulec (imikulec) wrote on 2016-12-14:

cards.tar.gz Edit (11.1 KiB, application/x-tar)

Revision history for this message

Olivier Mattelaer (olivier-mattelaer) wrote on 2016-12-15: Re: [Bug 1649834] [NEW] Pathological behaviour of stop decay

Download full text (5.5 KiB)

Hi,

Can you cross-check with 2.5.2.
This is similar to a previous bug that we have solve. Now I do not remember this such bug ws fixed before or after 2.4.2

Note that the bug here is actually that such particle should not be written in the lhe file,
> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:

Note that in itself they are noting wrong in that kinematic.
But indeed this particle should indeed not be written in the lhef file, which might indicate a deeper problem.

Cheers,

Olivier

> On Dec 14, 2016, at 19:05, Ivan Mikulec <email address hidden> wrote:
>
> Public bug reported:
>
> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>
> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
> 10 0 0.3811600E+18 0.4684444E+03 0.7816531E-02 0.1031579E+00
> 21 -1 0 0 503 502 0.00000000000E+00 0.00000000000E+00 0.35396361746E+03 0.35396361746E+03 0.00000000000E+00 0. -1.
> 21 -1 0 0 504 503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03 0.53577878135E+03 0.00000000000E+00 0. -1.
> 1000006 2 1 2 504 0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03 0.52848713534E+03 0.42764970339E+03 0. 0.
> 1000006 2 3 3 501 0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03 0.41652361491E+03 0.30000000000E+03 0. 0.
> -1000006 2 1 2 0 502 0.14922534112E+03 0.11953115858E+03 0.62844769711E+02 0.36125526347E+03 0.30000000000E+03 0. 0.
> 6 1 4 4 501 0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03 0.24718399018E+03 0.17500000000E+03 0. -1.
> 1000022 1 4 4 0 0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02 0.16933962473E+03 0.10000000000E+03 0. 1.
> -6 1 5 5 0 502 0.11330615545E+03 0.13433345929E+03 0.52233287346E+02 0.25345034909E+03 0.17500000000E+03 0. -1.
> 1000022 1 5 5 0 0 0.35919185669E+02 -0.14802300712E+02 0.10611482366E+02 0.10780491438E+03 0.10000000000E+03 0. 1.
> 21 1 3 3 504 501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02 0.11196352043E+03 0.00000000000E+00 0. -1.
>
> The stop decay width is set to be very narrow. Please, note also that
> this happens only to stops and not to anti-stops. This type of events
> are absent if we do not ask for the stop to decay. We tested this up to
> the MG version 2.4.2. The cards we used in this example are attached. To
> us this looks like a bug but we would like to ask you for an opinion.
>
> ** Affects: mg5amcnlo
> Importance: Undecided
> Status: New
>
> ** Attachment added: "cards.tar.gz"
> https://bugs.launchpad.net/bugs/1649834/+attachment/4791502/+files/cards.tar.gz
>
> --
> You received this bug notification because you are subscribed to
> MadGraph5_aMC@NLO.
> https://bugs.la...

Hi Olivier,

Best,
Ivan

> On 15 Dec 2016, at 02:48, Olivier Mattelaer <olivier.mattelaer@uclouvain.be> wrote:
> 
> Hi,
> 
> Can you cross-check with 2.5.2. 
> This is similar to a previous bug that we have solve. Now I  do not remember this such bug ws fixed before or after 2.4.2
> 
> Note that the bug here is actually that such particle should not be written in the lhe file, 
>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
> 
> Note that in itself they are noting wrong in that kinematic.
> But indeed this particle should indeed not be written in the lhef file, which might indicate a deeper problem.
> 
> 
> Cheers,
> 
> Olivier
> 
> 
>> On Dec 14, 2016, at 19:05, Ivan Mikulec <1649834@bugs.launchpad.net> wrote:
>> 
>> Public bug reported:
>> 
>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>> 
>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>     21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>     21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>> 1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>> 1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>      6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>> 1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>     -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>> 1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>     21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>> 
>> The stop decay width is set to be very narrow. Please, note also that
>> this happens only to stops and not to anti-stops. This type of events
>> are absent if we do not ask for the stop to decay. We tested this up to
>> the MG version 2.4.2. The cards we used in this example are attached. To
>> us this looks like a bug but we would like to ask you for an opinion.
>> 
>> ** Affects: mg5amcnlo
>>    Importance: Undecided
>>        Status: New
>> 
>> ** Attachment added: "cards.tar.gz"
>>  https://bugs.launchpad.net/bugs/1649834/+attachment/4791502/+files/cards.tar.gz
>> 
>> -- 
>> You received this bug notification because you are subscribed to
>> MadGraph5_aMC@NLO.
>> https://bugs.launchpad.net/bugs/1649834
>> 
>> Title:
>> Pathological behaviour of stop decay
>> 
>> Status in MadGraph5_aMC@NLO:
>> New
>> 
>> Bug description:
>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>> 
>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>       21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>       21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>>  1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>>  1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>        6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>>  1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>       -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>>  1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>       21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>> 
>> The stop decay width is set to be very narrow. Please, note also that
>> this happens only to stops and not to anti-stops. This type of events
>> are absent if we do not ask for the stop to decay. We tested this up
>> to the MG version 2.4.2. The cards we used in this example are
>> attached. To us this looks like a bug but we would like to ask you for
>> an opinion.
>> 
>> To manage notifications about this bug go to:
>> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions
> 
> -- 
> You received this bug notification because you are subscribed to the bug
> report.
> https://bugs.launchpad.net/bugs/1649834
> 
> Title:
>  Pathological behaviour of stop decay
> 
> Status in MadGraph5_aMC@NLO:
>  New
> 
> Bug description:
>  When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>  generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
> 
>  a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>  10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>        21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>        21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>   1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>   1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>  -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>         6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>   1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>        -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>   1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>        21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
> 
>  The stop decay width is set to be very narrow. Please, note also that
>  this happens only to stops and not to anti-stops. This type of events
>  are absent if we do not ask for the stop to decay. We tested this up
>  to the MG version 2.4.2. The cards we used in this example are
>  attached. To us this looks like a bug but we would like to ask you for
>  an opinion.
> 
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions

Revision history for this message

Olivier Mattelaer (olivier-mattelaer) wrote on 2016-12-19:

Download full text (11.8 KiB)

Hi,

Here is a patch to avoid that such second entry appears in the lhe file.

=== modified file 'Template/LO/SubProcesses/myamp.f'
--- Template/LO/SubProcesses/myamp.f 2016-10-03 09:56:24 +0000
+++ Template/LO/SubProcesses/myamp.f 2016-12-17 10:23:26 +0000
@@ -273,9 +273,6 @@
            if (onshell .and. (lbw(nbw).eq. 2) .or.
     $ .not. onshell .and. (lbw(nbw).eq. 1)) then
               cut_bw=.true.
- if (gForceBW(i, iconfig).eq.1) then
- return
- endif
c write(*,*) 'cut_bw: ',nbw,xmass,onshell,lbw(nbw),cut_bw
            endif
         endif

I believe that such bug does not have any effect at parton level. (cross-section/distribution)
but can induce some effect when running the parton-shower.

Cheers,

Olivier

> On Dec 16, 2016, at 13:32, Ivan Mikulec <email address hidden> wrote:
>
> Hi Olivier,
>
> the cross-sheck with 2.5.2 gives the same result, so this particular bug
> does not seem to be fixed. I would like to point out again that the
> described effect appears only for stops and not for anti-stops.
>
> Best,
> Ivan
>
>> On 15 Dec 2016, at 02:48, Olivier Mattelaer <email address hidden> wrote:
>>
>> Hi,
>>
>> Can you cross-check with 2.5.2.
>> This is similar to a previous bug that we have solve. Now I do not remember this such bug ws fixed before or after 2.4.2
>>
>> Note that the bug here is actually that such particle should not be written in the lhe file,
>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>
>> Note that in itself they are noting wrong in that kinematic.
>> But indeed this particle should indeed not be written in the lhef file, which might indicate a deeper problem.
>>
>>
>> Cheers,
>>
>> Olivier
>>
>>
>>> On Dec 14, 2016, at 19:05, Ivan Mikulec <email address hidden> wrote:
>>>
>>> Public bug reported:
>>>
>>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>>>
>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>> 10 0 0.3811600E+18 0.4684444E+03 0.7816531E-02 0.1031579E+00
>>> 21 -1 0 0 503 502 0.00000000000E+00 0.00000000000E+00 0.35396361746E+03 0.35396361746E+03 0.00000000000E+00 0. -1.
>>> 21 -1 0 0 504 503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03 0.53577878135E+03 0.00000000000E+00 0. -1.
>>> 1000006 2 1 2 504 0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03 0.52848713534E+03 0.42764970339E+03 0. 0.
>>> 1000006 2 3 3 501 0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03 0.41652361491E+03 0.30000000000E+03 0. 0.
>>> -1000006 2 1 2 0 502 0.14922534112E+03 0.11953115858E+03 0.62844769711E+02 0.36125526347E+03 0.30000000000E+03 0. 0.
>>> 6 1 4 4 501 0 -0.45063651629E+02 -0.10161421547E+03 ...

Hi,

Here is a patch to avoid that such second entry appears in the lhe file.

=== modified file 'Template/LO/SubProcesses/myamp.f'
--- Template/LO/SubProcesses/myamp.f	2016-10-03 09:56:24 +0000
+++ Template/LO/SubProcesses/myamp.f	2016-12-17 10:23:26 +0000
@@ -273,9 +273,6 @@
            if (onshell .and. (lbw(nbw).eq. 2) .or.
     $          .not. onshell .and. (lbw(nbw).eq. 1)) then
               cut_bw=.true.
-               if (gForceBW(i, iconfig).eq.1) then
-                  return
-               endif
c               write(*,*) 'cut_bw: ',nbw,xmass,onshell,lbw(nbw),cut_bw
            endif
         endif

I believe that such bug does not have any effect at parton level. (cross-section/distribution)
but can induce some effect when running the parton-shower.

Cheers,

Olivier

> On Dec 16, 2016, at 13:32, Ivan Mikulec <1649834@bugs.launchpad.net> wrote:
> 
> Hi Olivier,
> 
> the cross-sheck with 2.5.2 gives the same result, so this particular bug
> does not seem to be fixed. I would like to point out again that the
> described effect appears only for stops and not for anti-stops.
> 
> Best,
> Ivan
> 
>> On 15 Dec 2016, at 02:48, Olivier Mattelaer <olivier.mattelaer@uclouvain.be> wrote:
>> 
>> Hi,
>> 
>> Can you cross-check with 2.5.2. 
>> This is similar to a previous bug that we have solve. Now I  do not remember this such bug ws fixed before or after 2.4.2
>> 
>> Note that the bug here is actually that such particle should not be written in the lhe file, 
>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>> 
>> Note that in itself they are noting wrong in that kinematic.
>> But indeed this particle should indeed not be written in the lhef file, which might indicate a deeper problem.
>> 
>> 
>> Cheers,
>> 
>> Olivier
>> 
>> 
>>> On Dec 14, 2016, at 19:05, Ivan Mikulec <1649834@bugs.launchpad.net> wrote:
>>> 
>>> Public bug reported:
>>> 
>>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>>> 
>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>>   21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>>   21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>>> 1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>>> 1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>>    6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>>> 1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>>   -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>>> 1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>>   21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>>> 
>>> The stop decay width is set to be very narrow. Please, note also that
>>> this happens only to stops and not to anti-stops. This type of events
>>> are absent if we do not ask for the stop to decay. We tested this up to
>>> the MG version 2.4.2. The cards we used in this example are attached. To
>>> us this looks like a bug but we would like to ask you for an opinion.
>>> 
>>> ** Affects: mg5amcnlo
>>>  Importance: Undecided
>>>      Status: New
>>> 
>>> ** Attachment added: "cards.tar.gz"
>>> https://bugs.launchpad.net/bugs/1649834/+attachment/4791502/+files/cards.tar.gz
>>> 
>>> -- 
>>> You received this bug notification because you are subscribed to
>>> MadGraph5_aMC@NLO.
>>> https://bugs.launchpad.net/bugs/1649834
>>> 
>>> Title:
>>> Pathological behaviour of stop decay
>>> 
>>> Status in MadGraph5_aMC@NLO:
>>> New
>>> 
>>> Bug description:
>>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>>> 
>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>>     21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>>     21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>>> 1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>>> 1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>>      6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>>> 1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>>     -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>>> 1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>>     21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>>> 
>>> The stop decay width is set to be very narrow. Please, note also that
>>> this happens only to stops and not to anti-stops. This type of events
>>> are absent if we do not ask for the stop to decay. We tested this up
>>> to the MG version 2.4.2. The cards we used in this example are
>>> attached. To us this looks like a bug but we would like to ask you for
>>> an opinion.
>>> 
>>> To manage notifications about this bug go to:
>>> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions
>> 
>> -- 
>> You received this bug notification because you are subscribed to the bug
>> report.
>> https://bugs.launchpad.net/bugs/1649834
>> 
>> Title:
>> Pathological behaviour of stop decay
>> 
>> Status in MadGraph5_aMC@NLO:
>> New
>> 
>> Bug description:
>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>> 
>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>      21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>      21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>> 1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>> 1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>       6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>> 1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>      -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>> 1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>      21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>> 
>> The stop decay width is set to be very narrow. Please, note also that
>> this happens only to stops and not to anti-stops. This type of events
>> are absent if we do not ask for the stop to decay. We tested this up
>> to the MG version 2.4.2. The cards we used in this example are
>> attached. To us this looks like a bug but we would like to ask you for
>> an opinion.
>> 
>> To manage notifications about this bug go to:
>> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions
> 
> -- 
> You received this bug notification because you are subscribed to
> MadGraph5_aMC@NLO.
> https://bugs.launchpad.net/bugs/1649834
> 
> Title:
> Pathological behaviour of stop decay
> 
> Status in MadGraph5_aMC@NLO:
> New
> 
> Bug description:
> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
> 
> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>       21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>       21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>  1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>  1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>        6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>  1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>       -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>  1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>       21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
> 
> The stop decay width is set to be very narrow. Please, note also that
> this happens only to stops and not to anti-stops. This type of events
> are absent if we do not ask for the stop to decay. We tested this up
> to the MG version 2.4.2. The cards we used in this example are
> attached. To us this looks like a bug but we would like to ask you for
> an opinion.
> 
> To manage notifications about this bug go to:
> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions

Revision history for this message

Ivan Mikulec (imikulec) wrote on 2017-01-11:

Download full text (12.1 KiB)

Hi Olivier,

the patch you sent me fixes the bug. Thank you!

Best,
Ivan

Hi Olivier,

the patch you sent me fixes the bug. Thank you!

Best,
Ivan

On 12/19/2016 12:28 PM, Olivier Mattelaer wrote:
> Hi,
>
> Here is a patch to avoid that such second entry appears in the lhe file.
>
> === modified file 'Template/LO/SubProcesses/myamp.f'
> --- Template/LO/SubProcesses/myamp.f	2016-10-03 09:56:24 +0000
> +++ Template/LO/SubProcesses/myamp.f	2016-12-17 10:23:26 +0000
> @@ -273,9 +273,6 @@
>              if (onshell .and. (lbw(nbw).eq. 2) .or.
>       $          .not. onshell .and. (lbw(nbw).eq. 1)) then
>                 cut_bw=.true.
> -               if (gForceBW(i, iconfig).eq.1) then
> -                  return
> -               endif
> c               write(*,*) 'cut_bw: ',nbw,xmass,onshell,lbw(nbw),cut_bw
>              endif
>           endif
>
> I believe that such bug does not have any effect at parton level. (cross-section/distribution)
> but can induce some effect when running the parton-shower.
>
> Cheers,
>
> Olivier
>
>> On Dec 16, 2016, at 13:32, Ivan Mikulec <1649834@bugs.launchpad.net> wrote:
>>
>> Hi Olivier,
>>
>> the cross-sheck with 2.5.2 gives the same result, so this particular bug
>> does not seem to be fixed. I would like to point out again that the
>> described effect appears only for stops and not for anti-stops.
>>
>> Best,
>> Ivan
>>
>>> On 15 Dec 2016, at 02:48, Olivier Mattelaer <olivier.mattelaer@uclouvain.be> wrote:
>>>
>>> Hi,
>>>
>>> Can you cross-check with 2.5.2.
>>> This is similar to a previous bug that we have solve. Now I  do not remember this such bug ws fixed before or after 2.4.2
>>>
>>> Note that the bug here is actually that such particle should not be written in the lhe file,
>>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>> Note that in itself they are noting wrong in that kinematic.
>>> But indeed this particle should indeed not be written in the lhef file, which might indicate a deeper problem.
>>>
>>>
>>> Cheers,
>>>
>>> Olivier
>>>
>>>
>>>> On Dec 14, 2016, at 19:05, Ivan Mikulec <1649834@bugs.launchpad.net> wrote:
>>>>
>>>> Public bug reported:
>>>>
>>>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>>>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>>>>
>>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>>>    21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>>>    21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>>>> 1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>>>> 1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>>>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>>>     6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>>>> 1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>>>    -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>>>> 1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>>>    21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>>>>
>>>> The stop decay width is set to be very narrow. Please, note also that
>>>> this happens only to stops and not to anti-stops. This type of events
>>>> are absent if we do not ask for the stop to decay. We tested this up to
>>>> the MG version 2.4.2. The cards we used in this example are attached. To
>>>> us this looks like a bug but we would like to ask you for an opinion.
>>>>
>>>> ** Affects: mg5amcnlo
>>>>   Importance: Undecided
>>>>       Status: New
>>>>
>>>> ** Attachment added: "cards.tar.gz"
>>>> https://bugs.launchpad.net/bugs/1649834/+attachment/4791502/+files/cards.tar.gz
>>>>
>>>> -- 
>>>> You received this bug notification because you are subscribed to
>>>> MadGraph5_aMC@NLO.
>>>> https://bugs.launchpad.net/bugs/1649834
>>>>
>>>> Title:
>>>> Pathological behaviour of stop decay
>>>>
>>>> Status in MadGraph5_aMC@NLO:
>>>> New
>>>>
>>>> Bug description:
>>>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>>>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>>>>
>>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>>>      21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>>>      21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>>>> 1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>>>> 1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>>>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>>>       6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>>>> 1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>>>      -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>>>> 1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>>>      21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>>>>
>>>> The stop decay width is set to be very narrow. Please, note also that
>>>> this happens only to stops and not to anti-stops. This type of events
>>>> are absent if we do not ask for the stop to decay. We tested this up
>>>> to the MG version 2.4.2. The cards we used in this example are
>>>> attached. To us this looks like a bug but we would like to ask you for
>>>> an opinion.
>>>>
>>>> To manage notifications about this bug go to:
>>>> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions
>>> -- 
>>> You received this bug notification because you are subscribed to the bug
>>> report.
>>> https://bugs.launchpad.net/bugs/1649834
>>>
>>> Title:
>>> Pathological behaviour of stop decay
>>>
>>> Status in MadGraph5_aMC@NLO:
>>> New
>>>
>>> Bug description:
>>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>>>
>>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>>       21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>>       21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>>> 1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>>> 1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>>        6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>>> 1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>>       -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>>> 1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>>       21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>>>
>>> The stop decay width is set to be very narrow. Please, note also that
>>> this happens only to stops and not to anti-stops. This type of events
>>> are absent if we do not ask for the stop to decay. We tested this up
>>> to the MG version 2.4.2. The cards we used in this example are
>>> attached. To us this looks like a bug but we would like to ask you for
>>> an opinion.
>>>
>>> To manage notifications about this bug go to:
>>> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions
>> -- 
>> You received this bug notification because you are subscribed to
>> MadGraph5_aMC@NLO.
>> https://bugs.launchpad.net/bugs/1649834
>>
>> Title:
>> Pathological behaviour of stop decay
>>
>> Status in MadGraph5_aMC@NLO:
>> New
>>
>> Bug description:
>> When trying to generate stops with an extra parton with a subsequent stop decay, e.g.:
>> generate p p > t1 t1~ g, t1 > t n1 / b1 b2 x1+ x2+ h+, t1~ > t~ n1 / b1~ b2~ x1- x2- h-
>>
>> a small part of stops (~0.5%) is generated with an unexpectedly high mass, radiates a gluon while the mass of the final stop drops to the desired value (here 300 GeV), e.g.:
>> 10   0  0.3811600E+18  0.4684444E+03  0.7816531E-02  0.1031579E+00
>>        21   -1    0    0  503  502  0.00000000000E+00 0.00000000000E+00  0.35396361746E+03  0.35396361746E+03 0.00000000000E+00 0. -1.
>>        21   -1    0    0  504  503 -0.00000000000E+00 -0.00000000000E+00 -0.53577878135E+03  0.53577878135E+03 0.00000000000E+00 0. -1.
>>   1000006    2    1    2  504    0 -0.14922534112E+03 -0.11953115858E+03 -0.24465993360E+03  0.52848713534E+03 0.42764970339E+03 0.  0.
>>   1000006    2    3    3  501    0 -0.14344205010E+03 -0.19292274283E+03 -0.16030319816E+03  0.41652361491E+03 0.30000000000E+03 0.  0.
>> -1000006    2    1    2    0  502  0.14922534112E+03 0.11953115858E+03  0.62844769711E+02  0.36125526347E+03 0.30000000000E+03 0.  0.
>>         6    1    4    4  501    0 -0.45063651629E+02 -0.10161421547E+03 -0.13460588218E+03  0.24718399018E+03 0.17500000000E+03 0. -1.
>>   1000022    1    4    4    0    0 -0.98378398474E+02 -0.91308527367E+02 -0.25697315976E+02  0.16933962473E+03 0.10000000000E+03 0.  1.
>>        -6    1    5    5    0  502  0.11330615545E+03 0.13433345929E+03  0.52233287346E+02  0.25345034909E+03 0.17500000000E+03 0. -1.
>>   1000022    1    5    5    0    0  0.35919185669E+02 -0.14802300712E+02  0.10611482366E+02  0.10780491438E+03 0.10000000000E+03 0.  1.
>>        21    1    3    3  504  501 -0.57832910148E+01 0.73391584250E+02 -0.84356735437E+02  0.11196352043E+03 0.00000000000E+00 0. -1.
>>
>> The stop decay width is set to be very narrow. Please, note also that
>> this happens only to stops and not to anti-stops. This type of events
>> are absent if we do not ask for the stop to decay. We tested this up
>> to the MG version 2.4.2. The cards we used in this example are
>> attached. To us this looks like a bug but we would like to ask you for
>> an opinion.
>>
>> To manage notifications about this bug go to:
>> https://bugs.launchpad.net/mg5amcnlo/+bug/1649834/+subscriptions

Olivier Mattelaer (olivier-mattelaer) on 2017-02-06