MadGraph5_aMC@NLO Generator

FCNC z-prime may not be working well since MadGraph5_v1_4_3?

Asked by Ezequiel Alvarez on 2012-05-15

Hello,

Since version 5.1.4.3 I observe that when introducing a new model (à la v4) with FCNC Z', it does not work well. For instance, when the coupling is set to zero, gives a non-sense cross section in tt~ production.

These are my files (only relevant lines showing):

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
particles.dat:
#MODEL EXTENSION
zp zp V W zpm zpw S zp 2198

interactions.dat:
# USRVertex
u t zp gzp QED
t u zp gzp QED

VariableName.dat:
fr

couplings.f:
c************************************
c UserMode couplings
c************************************

      gzp(1)=dcmplx(1d0,Zero)
      gzp(2)=dcmplx(fr,Zero)

That is for the model. Then, in the working directory:

Cards/proc_card_mg5.dat:
import model_v4 zprime
...
generate p p > t t~ QED=2 @1

Cards/param_card.dat:
BLOCK MGUSER
         1 0.00000000e+00 # fr,

Cards/run_card.dat
     4000 = ebeam1 ! beam 1 energy in GeV
     4000 = ebeam2 ! beam 2 energy in GeV

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

So well, the issue comes when I run ./bin/generate_events since it gives me a cross section of 668 pb. (This is wrong, if the coupling fr=0 then it should be the SM cross-section that for these energies is ~130 pb.) Moreover, when I look the contributions to the 668 pb cross sections I see that the main contribution (515 pb) comes from the t-channel Z' FCNC, which should not be present, since the coupling fr is set to zero. However, if I set the Z' mass very large in param_card.dat, then yes it retrieves the SM cross section.

I am confused: if the coupling fr is set to 0, it should retrieve the SM cross section, right?

Thanks for your great software, and for your great availability here in launchpad,

Ezequiel Alvarez.

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
No assignee Edit question
Solved by:
Ezequiel Alvarez
Solved:
2012-05-15
Last query:
2012-05-15
Last reply:
2012-05-15

Hi Ezequiel,

Could you send me your model (and the process that you check).
[olivier.mattelaer_AT_uclouvain.be]

I'm going to run this on my laptop to see what the problem is.

Cheers,

Olivier

On 15-mai-12, at 11:25, Ezequiel Alvarez wrote:

> New question #197342 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/197342
>
> Hello,
>
> Since version 5.1.4.3 I observe that when introducing a new model (à
> la v4) with FCNC Z', it does not work well. For instance, when the
> coupling is set to zero, gives a non-sense cross section in tt~
> production.
>
> These are my files (only relevant lines showing):
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> particles.dat:
> #MODEL EXTENSION
> zp zp V W zpm zpw S zp 2198
>
> interactions.dat:
> # USRVertex
> u t zp gzp QED
> t u zp gzp QED
>
> VariableName.dat:
> fr
>
> couplings.f:
> c************************************
> c UserMode couplings
> c************************************
>
> gzp(1)=dcmplx(1d0,Zero)
> gzp(2)=dcmplx(fr,Zero)
>
> That is for the model. Then, in the working directory:
>
> Cards/proc_card_mg5.dat:
> import model_v4 zprime
> ...
> generate p p > t t~ QED=2 @1
>
> Cards/param_card.dat:
> BLOCK MGUSER
> 1 0.00000000e+00 # fr,
>
> Cards/run_card.dat
> 4000 = ebeam1 ! beam 1 energy in GeV
> 4000 = ebeam2 ! beam 2 energy in GeV
>
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> So well, the issue comes when I run ./bin/generate_events since it
> gives me a cross section of 668 pb. (This is wrong, if the coupling
> fr=0 then it should be the SM cross-section that for these energies
> is ~130 pb.) Moreover, when I look the contributions to the 668 pb
> cross sections I see that the main contribution (515 pb) comes from
> the t-channel Z' FCNC, which should not be present, since the
> coupling fr is set to zero. However, if I set the Z' mass very
> large in param_card.dat, then yes it retrieves the SM cross section.
>
> I am confused: if the coupling fr is set to 0, it should retrieve
> the SM cross section, right?
>
> Thanks for your great software, and for your great availability
> here in launchpad,
>
> Ezequiel Alvarez.
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Ezequiel Alvarez (sequi76) said : #2

Hi Olivier,

I think I've found MY mistake. Don't spend your time running
anything, I'll update in a while my report. Thanks, Ezequiel.

On Tue, May 15, 2012 at 10:15 AM, Olivier Mattelaer
<email address hidden> wrote:
> Your question #197342 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/197342
>
>    Status: Open => Answered
>
> Olivier Mattelaer proposed the following answer:
> Hi Ezequiel,
>
> Could you send me your model (and the process that you check).
> [olivier.mattelaer_AT_uclouvain.be]
>
> I'm going to run this on my laptop to see what the problem is.
>
> Cheers,
>
> Olivier
>
> On 15-mai-12, at 11:25, Ezequiel Alvarez wrote:
>
>> New question #197342 on MadGraph5:
>> https://answers.launchpad.net/madgraph5/+question/197342
>>
>> Hello,
>>
>> Since version 5.1.4.3 I observe that when introducing a new model (à
>> la v4) with FCNC Z', it does not work well.  For instance, when the
>> coupling is set to zero, gives a non-sense cross section in tt~
>> production.
>>
>> These are my files (only relevant lines showing):
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>> particles.dat:
>> #MODEL EXTENSION
>> zp       zp       V        W      zpm    zpw     S   zp   2198
>>
>> interactions.dat:
>> #   USRVertex
>> u  t  zp  gzp  QED
>> t  u  zp  gzp  QED
>>
>> VariableName.dat:
>> fr
>>
>> couplings.f:
>> c************************************
>> c UserMode couplings
>> c************************************
>>
>>      gzp(1)=dcmplx(1d0,Zero)
>>      gzp(2)=dcmplx(fr,Zero)
>>
>> That is for the model.  Then, in the working directory:
>>
>> Cards/proc_card_mg5.dat:
>> import model_v4 zprime
>> ...
>> generate p p > t t~ QED=2 @1
>>
>> Cards/param_card.dat:
>> BLOCK MGUSER
>>         1     0.00000000e+00   # fr,
>>
>> Cards/run_card.dat
>>     4000     = ebeam1  ! beam 1 energy in GeV
>>     4000     = ebeam2  ! beam 2 energy in GeV
>>
>> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>>
>> So well, the issue comes when I run ./bin/generate_events since it
>> gives me a cross section of 668 pb.  (This is wrong, if the coupling
>> fr=0 then it should be the SM cross-section that for these energies
>> is ~130 pb.) Moreover,  when I look the contributions to the 668 pb
>> cross sections I see that the main contribution (515 pb) comes from
>> the t-channel Z' FCNC, which should not be present, since the
>> coupling fr is set to zero.  However, if I set the Z' mass very
>> large in param_card.dat, then yes it retrieves the SM cross section.
>>
>> I am confused: if the coupling fr is set to 0, it should retrieve
>> the SM cross section, right?
>>
>> Thanks for your great software, and for your great  availability
>> here in launchpad,
>>
>> Ezequiel Alvarez.
>>
>> --
>> You received this question notification because you are a member of
>> MadTeam, which is an answer contact for MadGraph5.
>
> --
> If this answers your question, please go to the following page to let us
> know that it is solved:
> https://answers.launchpad.net/madgraph5/+question/197342/+confirm?answer_id=0
>
> 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/madgraph5/+question/197342
>
> You received this question notification because you asked the question.

Ezequiel Alvarez (sequi76) said : #3

Hi Olivier,

I have found MY mistake: there was a "1d0" in the Left coupling in the couplings.f which I didn't set to Zero. I feel stupid.

Sorry about that, thanks again!

Bests,

Ezequiel.