problem with the cross section

Hi Andreas,

> After doing a few more tests, I noticed that the cross section is strongly connected with the width defined in the slha file.

Indeed in the narrow width approximation, the total cross-section is inversely proportional to the total width.
Since the branching ratio is nothing else that the partial width divided by the total width).
So indeed you expect that your cross-section to be strongly connected to the value of the total width.

> So my question is, how can I be sure which width to use in order to get the correct cross section? Is there any official way or should I start modifying the
> width until the cross section agrees with the one I get without specifying the decaying products (times the branching ratio)?

In principle, you need to use a width calculator in order to have the correct width associate to your mass spectrum prior to your calculation.
For mssm such calculator exist already on the market. I actually developing such tools for any (UFO) model (computation done at leading order).
This is not yet release, but if you want to test it, you are more than welcome:

You need to install bazaar on your computer then type the following command:
bzr branch lp:~maddevelopers/madgraph5/decay_calculator

then in you param_card you can set any width value to Auto.
and the code will automatically compute the corresponding width (and will determine automatically if it need to evaluate the 3/4 body decay)

Cheers,

Olivier

On Nov 17, 2013, at 7:26 PM, Andreas Petridis <email address hidden> wrote:

> New question #239366 on MadGraph5:
> https://answers.launchpad.net/madgraph5/+question/239366
>
> Dear experts,
>
> I am trying to generate direct gauging production p p > x1+ n2 and p p > x1- n2 with a small mass gap between
> the chargino1 (netraulino2) and neutralino1 but I am facing a problem with the cross section:
>
> I set the mass of mx1 = mN2 = 150 GeV and mN1 = 100 GeV in the slha file found in the MadGraph site.
> If I do not specify the decaying products, which means that I define the process as:
> generate p p > x1+ n2 @1
> add process p p > x1- n2 @2
>
> then I get a cross section of:
>
> Cross-section : 1.58 +- 0.01296 pb
>
> If I do specify the decaying products like below:
> generate p p > x1+ n2, x1+ > j j n1, n2 > l+ l- n1 @1
> add process p p > x1- n2, x1- > j j n1, n2 > l+ l- n1 @2
>
> then the cross section becomes very small
>
> Cross-section : 3.001e-09 +- 5.309e-11 pb
>
> and does not agree with the one I would expect which is: TotalCrossSection x BR(Z/gamma*->ll) x BR(W->qq) = 1.58*0.68*0.10 = 0.107 pb
>
> This issue does not seem to happen if the intermediate W/Z bosons are generated on shell which happens for larger mass gaps between
> chargino1 (netraulino2) and neutralino1.
>
> I have tried to modify the bwcutoff by giving a value of 10K and also set the cut_decays to false but still the cross section is the same as before…
> After doing a few more tests, I noticed that the cross section is strongly connected with the width defined in the slha file.
>
> So my question is, how can I be sure which width to use in order to get the correct cross section? Is there any official way or should I start modifying the
> width until the cross section agrees with the one I get without specifying the decaying products (times the branching ratio)?
>
> Any ideas on how to resolve this issue?
>
> Thank you in advance,
> A.P
>
>
> --
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> MadTeam, which is an answer contact for MadGraph5.

It seems like you're experiencing an issue with the cross-section on a construction site https://www.chessboardvault.com/best-chess-training-plan/ or a similar context. To address this problem, you may want to consider the following steps. First, double-check the accuracy of the measurements and data used to create the cross-section. Ensure that all relevant information, such as elevations and distances, is correct. If there are discrepancies, correct them before proceeding. Next, review the tools or software used to generate the cross-section to make sure they are functioning properly and are up-to-date. If the issue persists, consult with a site engineer or relevant professionals to get their input and expertise in troubleshooting the problem. It's crucial to address cross-section issues promptly to maintain the integrity and accuracy of the site's design and construction processes.