usage of DECAY package

Hi Valerio,

>was wondering where the Br of the W are decided and if it's possible to change them.
> Please note that I am not considering of forcing the W to decay in a particular particle (I saw that this is possible) but rather
> slightly change the W->lepton Br (and consequently the W->hadrons one).

If in the the header of the file you include the branching ratio information, the program should use it.
So you just have to edit the header of the file and change (and/or add this information).
Just to be complete the format is the following:

# PDG Width
DECAY 24 2.047910e+00
# BR NDA ID1 ID2 ...
   3.333605e-01 2 4 -3 # 0.682692239797
   3.333605e-01 2 2 -1 # 0.682692239797
   1.111202e-01 2 14 -13 # 0.227564079932
   1.111202e-01 2 12 -11 # 0.227564079932
   1.110388e-01 2 16 -15 # 0.227397411854

- is it possible to steer the execution of the program from a config file?
  Having to manually input all the time the type of decay and input/output file is not ideal for batch

The only solution is to pipe the command:
./decay < input_file
where you set the command in input_file.
I know this is not ideal, but this is an old program that are not going to be updated, so you will not have problem with modification of the code.

Cheers,

Olivier

Hi Olivier,

thanks for the answer.

The bit regarding the running of decay works smoothly and it's exactly what I needed.

Unfortunately I still seem to have problem with the modification of the Br.
I put the lines you suggested in the param_card.dat so that they will appear in every lhe file.

In order to test if they are working I modified the value to give 96% Br to tau (so that I can easily spot it).
But when inspecting the file results of the decay I see the 'usual' proportion for the decay modes.

I am quite bad at fortran but by looking at the code I would not find the place where br_w_lv is written in decay.f
For my application I can easily overwrite it manually, but I just wanted to make sure there is not an easier solution.

Do you have any idea of what I might be doing wrong?

thanks,

Valerio

Hi Valerio,

I've look at the code and indeed this seems to be hardcoded.
(decay_event line 1011):
         if(aa1.lt.3d0*br_w_lv) then !leptonic decay
            hadro_dec=.false.
            if(aa.lt.one/Three) then
               jd(jvl)=isign*12 !ve or ve~
               jd(jl) =isign*(-11) !e+ or e-
            elseif(aa.lt.two/three) then
               jd(jvl)=isign*14 !vm or vm~
               jd(jl) =isign*(-13) !mu+ or mu-
            else

So looks like that the only way is to modify the code by hand in this case.

Cheers,

Olivier

On Aug 18, 2013, at 2:41 PM, Valerio Dao <email address hidden> wrote:

> Question #233710 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/233710
>
> Status: Answered => Open
>
> Valerio Dao is still having a problem:
> Hi Olivier,
>
> thanks for the answer.
>
> The bit regarding the running of decay works smoothly and it's exactly
> what I needed.
>
> Unfortunately I still seem to have problem with the modification of the Br.
> I put the lines you suggested in the param_card.dat so that they will appear in every lhe file.
>
> In order to test if they are working I modified the value to give 96% Br to tau (so that I can easily spot it).
> But when inspecting the file results of the decay I see the 'usual' proportion for the decay modes.
>
> I am quite bad at fortran but by looking at the code I would not find the place where br_w_lv is written in decay.f
> For my application I can easily overwrite it manually, but I just wanted to make sure there is not an easier solution.
>
> Do you have any idea of what I might be doing wrong?
>
> thanks,
>
> Valerio
>
> --
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