MadGraph5_aMC@NLO

On-shell or off-shell processes?

Asked by Hilal

Dear Madgrpah team members,

I want to estimate corss section of of the final state b bbar + Emiss at the ILC, and I m so confused about the nature of the estimated cross section values by Madgraph. I got different values using the follwing commands:

1- MG5_aMC>generate e- e+ > b b~ vl vl~ / vl vl~ b b~

2 -MG5_aMC>generate e- e+ > b b~ vl vl~ / vl vl~

3- MG5_aMC>generate e- e+ > b b~ vl vl~ / b b~

4- MG5_aMC>generate e- e+ > b b~ vl vl~

When I run all these processes at sqrt(s)= 1 TeV, I found the following values : 0.61638 pb, 0.62056 pb, 0.3258 pb and 0.32369 pb respectively, and each process occurs via 23, 35, 31 and 43 diagrams, respectively.

I want to understand in which process, the Higgs and the Z,W gauge bosons are on-shell or off-shell?

In my work, I want to consider all the contributions to this final state, should I sum these process as

MG5_aMC>generate e- e+ > b b~ vl vl~ / vl vl~ b b~
MG5_aMC>add process e- e+ > b b~ vl vl~ / vl vl~
MG5_aMC>add process e- e+ > b b~ vl vl~ / b b~
MG5_aMC>add process e- e+ > b b~ vl vl~

Thanks in advance.

Hilal

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Olivier Mattelaer
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Best Olivier Mattelaer (olivier-mattelaer) said : 		#1

Those diagrams contains both some onshell and offshell contributions.

"add process e- e+ > b b~ vl vl~" should have all the Feynman Diagram included in the three other syntaxes.
So you can certainly not add such syntaxes with the "add diagram" without having some serious double counting.

In top of that I'm not sure that your syntax 1-3 is gauge invariant and lorentz invariant . But I did not check.

Cheers,

Olivier

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Hilal (hhamdell) said : 		#2

Thanks Olivier Mattelaer, that solved my question.