MadGraph5_aMC@NLO

Ecm cut in madgraph for p p collisions

Asked by Disha Bhatia

Hello,

I was trying to study a process which involves new physics contributions due to the trilinear higgs like couplings.
Since the dimension of coupling has one mass dimension, I need to restrict it such that it doesn't violate unitarity.

Is it possible withing the framework to put a cut of s_hat or Ecm for p p collisions?

Thanks,
Disha

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Olivier Mattelaer (olivier-mattelaer) said : 		#1

Hi,

We do not have such cut within the normal user-interface.
So you need to hack the code for doing that.

What I would TEST is the following:
in SubProcesses/genps.f
at line 737 you have
         smax = min((dsqrt(s(-nbranch))-totmass+sqrt(smin))**2, stot)
you can here replace that line by
         smax = min((dsqrt(s(-nbranch))-totmass+sqrt(smin))**2, MYCUT**2)

If it works as expected, please reported it here, I can consider to put a parameter in the run_card for future usage.

Cheers,

Olivier

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Disha Bhatia (dishabhatia1989) said : 		#2

Ok thank you. The command is running fine, there is no error but the cross-section values which I am getting are same by
changing stot values, I will try more with that.

Can we also by same means put a limit on s_min?

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Disha Bhatia (dishabhatia1989) said : 		#3

I now checked if I globally change the definition of stot in the code genps.f, then the cross-section is changing.
Instead of using the definition of stot == m1**2 + m2**2 +2*(pi1(0)*pi2(0)-pi1(3)*pi2(3))
If I put, stot = MYCUT**2, answer is changing.

But I am not sure whether this is ok to change at this level.

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Olivier Mattelaer (olivier-mattelaer) said : 		#4

Hi,

No modifying stot is equivalent to change the beam energy, so this is not a good idea.
I actually not have a good method to do it then.
The way to go is to implement it as a simple cuts in
SubProcesses/dummy_fcts.f

Cheers,

Olivier

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Disha Bhatia (dishabhatia1989) said : 		#5

Ok , let me see if it works.
Thanks a lot.

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