MadGraph5_aMC@NLO

Setting Minimum Center of Mass Energy (smin) at NLO

Asked by Richard Ruiz

Dear Experts,

I am trying to study boosted topologies and in particular ttbar +1j. Rather than inefficiently carving out a region of phase space with many, many cuts, I want to simply limit my phase space integration from a center of mass energy of \sqrt(s-hat) ~ 1 TeV.

For a leading order, this simply requires editing "smin" after the "smin do-loop" in SubProcesses/setcuts.f.

For NLO calculations, however, this is less clear to me because of the various "taumin_X" variables. It seems like "tau_Born_lower_bound" and "tau_lower_bound" are the correct terms (modulo division by "stot"). If this is correct, where exactly should this be done? The objects appear to written several times during the various kinematic checks.

On a related note, is it foreseeable that this cut be included in the default run_cards? I have in mind an additional setcut check that asks which is larger "smin" or "simin_defined_by_run_card" and simply starts the PDF integration from that point.

Thanks for all the suggestions and help. It is very much appreciated!

cheers
richard

Question information

Language:
English Edit question
Status:
Solved
For:
MadGraph5_aMC@NLO Edit question
Assignee:
Rikkert Frederix Edit question
Solved by:
Richard Ruiz
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Last reply:
Revision history for this message
Rikkert Frederix (frederix) said : 		#1

Dear Richard,

It all depends a bit on what you want to do. How do you define the centre-of-mass energy, sqrt(s-hat)? Do you include the extra parton that appears in the real-emission corrections in the definition? Or only the top--anti-top system? Are you including matching to the parton shower, or are you working at fixed order?

This is also the reason why we do not want to include this cut in the run-card. Moreover, sqrt(s-hat) is usually not a value that is directly accessible from an experimental point of view.

Best,
Rikkert

Revision history for this message
Richard Ruiz (rruiz) said : 		#2

Dear Rikkert,

Thank you for the reply. I have had time to think about your response more and realize that I had in mind, while well-defined at LO, an ill-defined quantity at NLO. Sorry for the trouble.

cheers
richard