Bridge

Dear Safinaz,

> May I ask about a package called BRIDGE could be installed with Madevent, could I use to calculate for
> example for a process p p > sr sr , sr > b b~ (with sr octet scalars) :

In principle BRIDGE can still be use for v4 model (but I'm not sure that scalar octet are supported by this model format)

> sigam( p p > sr sr ) * Branching ratio (sr > b b~ ) through Madevent ? I read about this package at Mad4 manual,
> but I understood from : why production and decay cross-section didn't agree FAQ for MadGraph5, that Madevent
> doesn't calculate BR because it dosn't use NWA ..

The question is why do you want to use an approximation when the full computation is available at roughly no cost.
In addition of the narrow-width approximation, the decay done by BRIDGE didn't have either the full spin-correlation.
(it only has the diagonal term of the density matrix).

Already a better possibility in your case is to use MadSpin: http://arxiv.org/abs/arXiv:1212.3460
which is include in the version 2.x of MG5_aMC@NLO.
This includes the full-spin correlation for the decay and include full off-shell effect.
The only approximation is that the total cross-section is not accurately computed and is based on the NWA, i.e.:
> sigam( p p > sr sr ) * Branching ratio (sr > b b~ )

But I strongly favor to simply use MG5 in this case, this is the most accurate and the most easy to use.

Cheers,

Olivier

On Nov 17, 2013, at 1:21 PM, Safinaz <email address hidden> wrote:

> Question #239349 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/239349
>
> Description changed to:
> Hi authors,
>
> May I ask about a package called BRIDGE could be installed with Madevent, could I use to calculate for
> example for a process p p > sr sr , sr > b b~ (with sr octet scalars) :
>
> sigam( p p > sr sr ) * Branching ratio (sr > b b~ ) through Madevent ? I read about this package at Mad4 manual,
> but I understood from : why production and decay cross-section didn't agree FAQ for MadGraph5, that Madevent
> dosn't calculate BR because it dosn't use NWA ..
>
> Thanks,
> Safinaz
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

Hi Dr.Olivier,

I'd like first to thank you for your answers about MG .

My question now for my process (p p > sr sr, sr > b b~ ) by MadEvent is that I get the total cross section ~ 10 pb
at ms = 2 TeV, while sigma ( p p > sr sr) ~ 10^-5 pb .. do you think that my result is sensible, I mean in case (sr > b b~)
is the dominant channel, the difference between using NWA or not can make all this difference ?

Regards,
Safinaz

Did you set the sr width correctly?
Looks like that width is not set correctly.

Cheers,

Olivier
On Nov 21, 2013, at 1:26 PM, Safinaz <email address hidden> wrote:

> Question #239349 on MadGraph5 changed:
> https://answers.launchpad.net/madgraph5/+question/239349
>
> Safinaz posted a new comment:
>
> Hi Dr.Olivier,
>
> I'd like first to thank you for your answers about MG .
>
> My question now for my process (p p > sr sr, sr > b b~ ) by MadEvent is that I get the total cross section ~ 10 pb
> at ms = 2 TeV, while sigma ( p p > sr sr) ~ 10^-5 pb .. do you think that my result is sensible, I mean in case (sr > b b~)
> is the dominant channel, the difference between using NWA or not can make all this difference ?
>
> Regards,
> Safinaz
>
> --
> You received this question notification because you are a member of
> MadTeam, which is an answer contact for MadGraph5.

I tried to write the decay width as Auto to the param_card
as : DECAY 40000 Auto # WSR , but it gives me the following error at launch MadEvent:

the UFO model does not include widths information. Impossible to compute widths automatically

I tried to set it from FR model, wrote "Width -> {WSR,Auto}" and it
appears in the param_card as : "DECAY 40000 1.000000e+00 # WSR ",

But it seems that's also not correct .. I know that the total decay width of sr
can reach at ms = 2 TeV to 6 * 10^2 GeV which is in principle Gamma(sr > b b~),
I think it's too large like that because Gamma is directly proportional to ms.

So now I can write the right total width to param_card or the FR model and
sigma(p p > sr sr, sr > b b~) gives ~ 10^-6 pb ..

Regards,
Safinaz