triplet diquark decays returns (PYCTTR:) colour tag tracing failed

Asked by Roberto Franceschini on 2012-03-26

Hello,
  generating a process using interactions with the color structure eps_ijk 3_i 3_j 3_k , as in the case of a di-quark color triplet, I manage to get events from MadEvent.

Unfortunately Pythia in pythia-pgs is unable to process these events to shower them and returns the error

     (PYCTTR:) colour tag tracing failed

I was wandering if there is a workaround to make pythia-pgs work with this kind of color connection, or I must process these events in a standalone shower (maybe Pythia 8 supports this structure of colors?)

Thanks for your answers!
Roberto

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Olivier Mattelaer
Solved:
2012-03-26
Last query:
2012-03-26
Last reply:
2012-03-26

Hi Roberto,

Indeed pyhtia6 doesn't support this type of color. In principle,
Pythia8 supports this types of color connections.
But this features was only tested on a couple of processes so I cann't
guarantee that this will work out of the box.

Please let us know if this is not working.

Cheers,

Olivier

On 26-mars-12, at 07:25, Roberto Franceschini wrote:

> New question #191718 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/191718
>
> Hello,
> generating a process using interactions with the color structure
> eps_ijk 3_i 3_j 3_k , as in the case of a di-quark color triplet, I
> manage to get events from MadEvent.
>
> Unfortunately Pythia in pythia-pgs is unable to process these events
> to shower them and returns the error
>
> (PYCTTR:) colour tag tracing failed
>
> I was wandering if there is a workaround to make pythia-pgs work
> with this kind of color connection, or I must process these events
> in a standalone shower (maybe Pythia 8 supports this structure of
> colors?)
>
> Thanks for your answers!
> Roberto
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Hi Roberto,

Indeed pyhtia6 doesn't support this type of color. In principle,
Pythia8 supports this types of color connections.
But this features was only tested on a couple of processes so I cann't
guarantee that this will work out of the box.

Please let us know if this is not working.

Cheers,

Olivier

On 26-mars-12, at 07:25, Roberto Franceschini wrote:

> New question #191718 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/191718
>
> Hello,
> generating a process using interactions with the color structure
> eps_ijk 3_i 3_j 3_k , as in the case of a di-quark color triplet, I
> manage to get events from MadEvent.
>
> Unfortunately Pythia in pythia-pgs is unable to process these events
> to shower them and returns the error
>
> (PYCTTR:) colour tag tracing failed
>
> I was wandering if there is a workaround to make pythia-pgs work
> with this kind of color connection, or I must process these events
> in a standalone shower (maybe Pythia 8 supports this structure of
> colors?)
>
> Thanks for your answers!
> Roberto
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Hi Olivier, thanks for your message. I see the issue. Some RPV SUSY process seems supported in pythia 6 but apparently not for the LHE input. I'll try if with Pythia 8 I have better luck ...
Thanks again
Cheers
Roberto

FabioMaltoni (fabio-maltoni) said : #4

Ciao Roberto,

we have checked a few things by now, both in production
and in decay and Pythia 8 worked. Let us know if it does not.
Thanks

Fabio

On 26 Mar 2012, at 15:40, Roberto Franceschini wrote:

> Question #191718 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/191718
>
> Roberto Franceschini posted a new comment:
> Hi Olivier, thanks for your message. I see the issue. Some RPV SUSY process seems supported in pythia 6 but apparently not for the LHE input. I'll try if with Pythia 8 I have better luck ...
> Thanks again
> Cheers
> Roberto
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Hey Fabio, great to read from you.
    thanks for checking that in Pythia 8.
I assume that you loaded the LHE and started Pythia from the LHE.
Ciao
Roberto

FabioMaltoni (fabio-maltoni) said : #6

Ciao Roberto,

yes. that's what was done..

Fabio

On 26 Mar 2012, at 16:30, Roberto Franceschini wrote:

> Question #191718 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/191718
>
> Roberto Franceschini posted a new comment:
> Hey Fabio, great to read from you.
> thanks for checking that in Pythia 8.
> I assume that you loaded the LHE and started Pythia from the LHE.
> Ciao
> Roberto
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Chris Brust (cpbrust) said : #7

Hi,

   I encountered a similar problem a few days ago; passing an LHE to pythia seems to let pythia get the spectrum and couplings, but it appears to be generating/decaying its own events instead of reading the output of MG5 (where I generated and decayed the events myself). Now, it's my understanding that pythia does isotropic decays instead of using matrix elements, which is not what I want. Is there any way to shower/hadronize the MG5 output directly?

   My best guess for a solution to this problem was to put "output pythia8" in the bottom of the proc_card, but newprocess_mg5 complains that what I have is a 2 -> 4 process, and it can only handle up to 2 -> 3.

   Thanks for your time, Chris

I passed my LHE to Pythia 8 and I manged to have top quarks in the final state to decay and also to get showering of my events produced with the espilon 333 color interaction.

Pythia did not complain of color connection issues and went through all the 10K events.

For the moment I should be fine, I hope no weird balls come out at analysis time ...

Thanks to all of you for your suggestions.
Cheers
Roberto

Thanks Olivier Mattelaer, that solved my question.

Johan Alwall (johan-alwall) said : #10

Dear Chris,

> I encountered a similar problem a few days ago; passing an LHE to pythia seems to let pythia get the spectrum and couplings, but it appears to be generating/decaying its own events instead of reading the output of MG5 (where I generated and decayed the events myself). Now, it's my understanding that pythia does isotropic decays instead of using matrix elements, which is not what I want. Is there any way to shower/hadronize the MG5 output directly?

This is not possible - if you use the MadGraph version of Pythia, it will read any events in the LHE file unless you explicitly open production channels in the pythia_card.dat (if you do, Pythia will switch to internal production instead of reading events from the LHE files). So just run MadGraph (specifying any decay chains in the process generation), and Pythia will do exactly what you want. If you still don't get it to work, please open a separate question, since this has nothing to do with the present question and it will make it easier for people to find it if they have a similar problem.

All the best,
Johan