New Particle Missing E_T

Hi Nick,

This is in fact a question for the pythia/pgs author respectively.
If you have an answer at a point don't hesitate to let me know, since as you know this is a recurrent question.

Cheers,

Olivier

On Jul 29, 2013, at 3:11 PM, Nick <email address hidden> wrote:

> New question #233214 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/233214
>
> My question concerns adding a stable fermion that is not self-conjugate and that should be considered as missing E_T by Pythia and PGS.
>
> Specifically, if I add this particle with a PDG number that is not currently assigned to any other particle, it is not recognized as missing E_T. Instead, the Pythia lhe file indicates that it is treated as an intermediate particle, and all the final-state particles are jets.
>
> One possible solution to this problem that has been discussed elsewhere (see links below) is to assign this particle the PDG code 1000022, the code for the lightest neutralino. However, this "hack" only works for self-conjugate particles, as the anti-particle with code -1000022 is not recognized as missing E_T. I also tried assigning it to code 18 -- a fourth generation neutrino -- but that was not recognized as missing E_T either, and the lhe file behaves the same as for an arbitrary, unassigned PDG code.
>
> Further discussion that I have found useful and similar to my problem include:
> https://answers.launchpad.net/madgraph5/+question/190668
> https://answers.launchpad.net/madgraph5/+question/222285
>
> However, as indicated above, neither of these links has solved my problem. So, my questions are:
> 1) Is there any PDG number that I can use for this new, stable, Dirac fermion, which Pythia and PGS will recognize as missing E_T?
> 2) If not, is there a way to tell Pythia and PGS to consider some arbitrary unassigned PDG number as missing E_T?
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

I think I have found the solution.

The problem appears to be in PGS. In the the file pythia-pgs/libraries/PGS4/src/pgslib.f, starting at line 1873, the particles that should be considered as "neutrino or non-interacting" are listed by PDG number. Adding an identical line of code with the appropriate number (in my case, I added 18) should fix the problem and allow PGS to recognize the new particle as missing E_T.

Thanks Nick,

This will be useful for a lot of people.

Cheers,

Olivier
On Jul 30, 2013, at 12:11 PM, Nick <email address hidden> wrote:

> Question #233214 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/233214
>
> Status: Answered => Solved
>
> Nick confirmed that the question is solved:
> I think I have found the solution.
>
> The problem appears to be in PGS. In the the file pythia-
> pgs/libraries/PGS4/src/pgslib.f, starting at line 1873, the particles
> that should be considered as "neutrino or non-interacting" are listed by
> PDG number. Adding an identical line of code with the appropriate
> number (in my case, I added 18) should fix the problem and allow PGS to
> recognize the new particle as missing E_T.
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.