# regarding scale choice in madgraph

Asked by Disha Bhatia on 2020-04-20

Hello,

Sorry for bothering you again during these pandemic times.
Actually I am considering jets+ met final states and wanted to set my scales to

pt_j1 + sqrt(ptj1^2 + m_{DM DMbar}^2).

I was trying to modify setscales.f
My DM is particle number 3, DMbar is particle number 4 and leading jet is particle number 5.

I gave commands like:

do i=0,3
pcomb(i) = p(i,3)+p(i,4)
enddo
q2factorization(1) = dsqrt(dot(pcomb,pcomb) +pt(P(0,5))**2) + pt(P(0,5))

However, I am getting error. I am not understanding how to construct invariant mass of two particles in setscales.
It would be really helpful, if you can explain me this. I didnt find any useful reference for this.

Thank you,
Disha

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Disha Bhatia
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2020-04-20
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2020-04-20
2020-04-20
 Olivier Mattelaer (olivier-mattelaer) said on 2020-04-20: #1

Hi,

the formula
dsqrt(dot(pcomb,pcomb) +pt(P(0,5))**2) + pt(P(0,5))

sounds fine. What is your error?

Cheers,

Olivier

 Disha Bhatia (dishabhatia1989) said on 2020-04-20: #2

I was defining pcomb as an array, it was complaining with error
"Fortran runtime error: Index '0' of dimension 1 of array 'pcomb' below lower bound of 1"
I was defining it as pcomb(4).

When I removed the dimension, and defined pcomb = p(0,3) + p(0,4) it is working fine.
I didn't understand how the four dimensions are taken care of in this definition.
I took help of how single particle mass was defined just in the example line in the setscales.f code.

 Olivier Mattelaer (olivier-mattelaer) said on 2020-04-20: #3

You need to define pcomb like this:
pcomb(0:3)

cheers,

Olivier

 Disha Bhatia (dishabhatia1989) said on 2020-04-20: #4

oh ok, thank you very much.