Cross section vs mass of a scalar

Hi,

Do I correctly understand your question, as:
How can I simulate off-shell effects for
> g g > S > a a

The parameter present in FR is the on shell mass not the invariant mass.
so with the above syntax madgraph will have the full breit-wigner dependence.

Cheers,

Olivier

> On Sep 8, 2016, at 16:22, Arash Yunesi <email address hidden> wrote:
>
> New question #387373 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/387373
>
> Hi
>
> I am trying to calculate "gg>S>diphoton" in which S is a gauge singlet scalar. In the first part of the diagram, S is generated through loop of a colored scalar particle (squark) and it decays to two photons through the same loop.
> I have used FeynRules to find UFO for the model. I have fixed mass of S in FeynRules input file, however what I like to do is to calculate gg>S>two photons vs mass of S.
> So what I am asking is that if it is possible to keep mass of S a variable and find UFO and tell MadGraph to calcualte cross section vs mass of S. Also I don't want to do this for on-shell S only. I know that my question might be related to FeynRules team.
> I appreciate any comments and advice.
>
> Arash
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.

First of all, your process is loop-induced, therefore make sure to read
arXiv:1507.00020
so as to learn about the caveats of generating a loop-compatible model with
FeynRules and NLOCT. More particularly, in this case you want to make sure
that your model includes the appropriate R2 counterterms.

Then, in your process definition, you must indicate that your process
occurs via a loop, otherwise MG5aMC will simply not find any tree-level
diagrams.
The correct process definition would be:

generate g g > S > a a [noborn=QCD]

Finally, you can change the mass at will by simply changing its value in
the param_card.dat for a particular run.
If you want to perform a scan over it, you can use the 'scan syntax' in the
param card, similarly to what is describe in the wiki page about
reweighting:

https://cp3.irmp.ucl.ac.be/projects/madgraph/wiki/Reweight

(see in particular the examples which use the syntax). Note that, of
course, the reweight module in itself is not an option for changing masses,
I mentioned this wiki page only so as to give you examples of the 'scan'
syntax usage.

So you can write something like this in the param_card.dat.

set mass 6 scan:[100,120,140,160,180]

On Thu, Sep 8, 2016 at 8:22 AM, Arash Yunesi <
<email address hidden>> wrote:

> New question #387373 on MadGraph5_aMC@NLO:
> https://answers.launchpad.net/mg5amcnlo/+question/387373
>
> Hi
>
> I am trying to calculate "gg>S>diphoton" in which S is a gauge singlet
> scalar. In the first part of the diagram, S is generated through loop of a
> colored scalar particle (squark) and it decays to two photons through the
> same loop.
> I have used FeynRules to find UFO for the model. I have fixed mass of S in
> FeynRules input file, however what I like to do is to calculate gg>S>two
> photons vs mass of S.
> So what I am asking is that if it is possible to keep mass of S a variable
> and find UFO and tell MadGraph to calcualte cross section vs mass of S.
> Also I don't want to do this for on-shell S only. I know that my question
> might be related to FeynRules team.
> I appreciate any comments and advice.
>
> Arash
>
> --
> You received this question notification because you are an answer
> contact for MadGraph5_aMC@NLO.
>

--
Valentin