color tracing problem with pythia 8

Hi,

This is a bug which is likely to be fixed in a more recent version of the code. (at least similar bugs have been fixed)

Cheers,

Olivier
> On Mar 23, 2016, at 19:32, Nikolay Kolev <email address hidden> wrote:
>
> New question #289139 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/289139
>
> I am trying to generate some events with monotop final state coming from a minimal extension of the standard model, including heavy colour-triplet scalars interacting with a light Majorana ferminon that can be dark matter (arxiv:1507.02271). The scalars are x1 (particle code 6000001) and x2 (particle code 6000002) and fermion is n (particle code 5000001). When I ask for extra jets in madgraph 2.2.3, some of the events fail in pythia 8210. The error messages are:
>
> 9420 Error in ColourTracing::traceFromAcol: colour tracing failed
> 4529 Error in ColourTracing::traceFromCol: colour tracing failed
> 181 Error in HadronLevel::next: failed colour/junction check
> 4710 Error in Pythia::next: hadronLevel failed; try again
>
> So it seems the problem is in color tracing. The events that fail are all from incoming (anti)quarks with a gluon coming from the incoming quarks or x, the lhe file does not have the complete information, so I cannot match the exact diagram. One suspect diagram is: incoming d~ and s~, d~ emits a gluon, d~ and s~ produce x1, x1 decays into t and n, t decays to W and b. The lhe file looks like this:
>
> <event>
> ...
> -1 -1 0 0 0 501 …
> -3 -1 0 0 0 502 …
> 6000001 2 1 2 504 0 ...
> 6 2 3 3 504 0 ...
> 5000001 1 3 3 0 0 ...
> 24 1 4 4 0 0 ...
> 5 1 4 4 504 0 ...
> 21 1 1 2 503 501 ...
> </event>
>
> It seems the gluon doesn't carry the right anticolor; changing 501 to 503 solves the issue; the event passes through pythia.
>
> So my question is: is this a problem or am I missing something in the model that is needed by madgraph to work out the color assignments?
>
>
>
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

Hi Olivier,

Thanks for the reply.

I downloaded the latest version 2.3.3 and still get the same errors.

Nikolay

So I downloaded the latest version 2.3.3 and still get the same errors.

Nikolay

Hi,

you can either try with the development version (that you can get via
bzr branch lp:~maddevelopers/mg5amcno/2.3.4

or give me the model that you test/ processes and i will test it myself.

Cheers,

Olivier

Thank you for your reply. So I installed madgraph 2.3.4 ad you suggested and still get the same error with the same frequency. What do you need to test it?

Nikolay

Hi,

I will need the model and the process definition (and potentially the benchmark point)

Thanks a lot for your help,

Olivier

Hi Olivier,

Sorry for the delay. I needed to get consent from my collaborators. Here is the model we are using and the param_card.dat. Let me know if anything else is necessary. Thank you for your help.

Nikolay

Dr. Nikolay Kolev

Department of Physics
University of Regina
3737 Wascana Parkway
Regina, Saskatchewan, S4S 0A2
Phone: 306-585-4262
Fax: 306-585-5659
<email address hidden>
http://tangra.phys.uregina.ca

On 2016-04-06, at 6:22 PM, Olivier Mattelaer <email address hidden> wrote:

> Your question #289139 on MadGraph5_aMC@NLO changed:
> https://answers.launchpad.net/mg5amcnlo/+question/289139
>
> Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Hi,
>
> I will need the model and the process definition (and potentially the
> benchmark point)
>
> Thanks a lot for your help,
>
> Olivier
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/mg5amcnlo/+question/289139/+confirm?answer_id=5
>
> If you still need help, you can reply to this email or go to the
> following page to enter your feedback:
> https://answers.launchpad.net/mg5amcnlo/+question/289139
>
> You received this question notification because you asked the question.

Hi Nikolay,

Attachment do not go trough the launchpad system.
Could you send it directly to my email?
<email address hidden>

Cheers,

Olivier

Thanks for the file.

Turns out that this a PY8 bug.
I have forward your problem to the PY8 responsible.

Cheers,

Olivier