Wino decays give zero cross section

Dear Michael,

Thanks for your question.
Olivier Mattelaer is away for a week and he aksed me to inform
the mg5 users that he will answer questions/comments on next Sunday.

Pierre

Hi Michael,

Did you try to compute the partial width
x1- > w- n1
Just to check that the associate coupling is different of zero for your param_card.

I suspect that this will not solve your problem, so could you send me by email your param_card/run_card such that I can reproduce your problem
and investigate by myself.

Cheers,

Olivier

On Apr 18, 2013, at 2:26 PM, Michael Flowerdew <email address hidden> wrote:

> New question #226979 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/226979
>
> Hello,
>
> I'm fairly new to MadGraph, trying to generate some SUSY events for a wino+wino- simplified model (within the ATLAS framework athena as it happens). This is my process card:
> ======================
> import model mssm
> # Define multiparticle labels
> define p = g u c d s u~ c~ d~ s~
> define j = g u c d s u~ c~ d~ s~
> define l+ = e+ mu+
> define l- = e- mu-
> define vl = ve vm vt
> define vl~ = ve~ vm~ vt~
> define fu = u c e+ mu+ ta+
> define fu~ = u~ c~ e- mu- ta-
> define fd = d s ve~ vm~ vt~
> define fd~ = d~ s~ ve vm vt
>
> # Specify process(es) to run
>
> generate p p > x1+ x1- $ go ul ur dl dr cl cr sl sr t1 t2 b1 b2 ul~ ur~ dl~ dr~ cl~ cr~ sl~ sr~ t1~ t2~ b1~ b2~ , x1+ > W+ n1 , x1- > W- n1 @0
> add process p p > x1+ x1- j $ go ul ur dl dr cl cr sl sr t1 t2 b1 b2 ul~ ur~ dl~ dr~ cl~ cr~ sl~ sr~ t1~ t2~ b1~ b2~ , x1+ > W+ n1 , x1- > W- n1 @1
>
> # Output processes to MadEvent directory
> output -f
> ======================
> If I omit the decays (removing literally ", x1+ > W+ n1 , x1- > W- n1") then everything works. For information, x1+ is a pure wino with m=800 GeV, n1 is a pure bino with m=500 GeV. With the card above, I get this error:
>
> Error detected in "generate_events -f Test"
> write debug file /ptmp/mpp/flowerde/MadGraphTest/MadGraphEvgenMySUSY/PROC_mssm_0/Test_fermi_debug.log
> If you need help with this issue please contact us on https://answers.launchpad.net/madgraph5
> MadGraph5Error : Survey return zero cross section.
> Typical reasons are the following:
> 1) A massive s-channel particle has a width set to zero.
> 2) The pdf are zero for at least one of the initial state particles.
> 3) The cuts are too strong.
> Please check/correct your param_card and/or your run_card.
>
> To me, the Test_fermi_debug.log file doesn't particularly add anything new. Taking these points one by one:
> 1) The specified decays are consistent with the associated SLHA file I provide, and the x1+ has a finite width.
> 2) Without decays, this works, and I don't see why the pdfs would change.
> 3) I saw that xqcut was perhaps a little high for W->qq decays (200 GeV), so I reduced it to 10 GeV - same error. I want to generate an inclusive sample, and I'm not aware of applying any cuts.
>
> I asked a couple of people I know, but they didn't know how to solve this either. Also, the solutions on this forum matching this error message don't appear to apply to my case. I'm happy to provide more details about my setup, I'm just not sure what would be most useful.
>
> Any help gratefully appreciated!
> Thanks,
> Mike
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Hi,

I'm not actually sure how to calculate just the width... I found a thread suggesting the following (for a Z' decay)
process zprime > x y @1
add process zprime > a b @2
so I did this and ran bin/generate_events again, but it just ran the cross section calculation with the same error. The same thread talked about running generate_decay_widths, but I cannot find this script. I've not been able to find any more information on the topic.

What should I do to make this work?

Cheers,
Mike

Hi Mike,

the ./bin/generate_events
is in fact equivalent to the following command:
./bin/madevent
MGME> launch

which for 2 > N process is equivalent to
./bin/madevent
MGME> generate_events
while for 1>N process this is equivalent to
./bin/madevent
MGME> calculate_decay_widths

"calculate_decay_widths" does the same stuff than "generate_events" except that It's not intended to generate events.

So this is not the problem at all in this case.

I've started to study your problem and it looks more complex than expected.

Cheers,

Olivier

On Apr 22, 2013, at 5:26 PM, Michael Flowerdew <email address hidden> wrote:

> Question #226979 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/226979
>
> Status: Answered => Open
>
> Michael Flowerdew is still having a problem:
> Hi,
>
> I'm not actually sure how to calculate just the width... I found a thread suggesting the following (for a Z' decay)
> process zprime > x y @1
> add process zprime > a b @2
> so I did this and ran bin/generate_events again, but it just ran the cross section calculation with the same error. The same thread talked about running generate_decay_widths, but I cannot find this script. I've not been able to find any more information on the topic.
>
> What should I do to make this work?
>
> Cheers,
> Mike
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Hello Olivier,

Thanks for looking into this. I've been a bit tied up with other things the last couple of days, but I'll send you my param_card and run_card now.

Cheers,
Mike