How to change the phase space point when checking amplitudes

Asked by Steven Jeremies on 2021-06-09

Hi,

I want to check the amplitude of a given process at a different phase-space point than the one which is given automatically after

> generate u b > d t H
> output standalone ubdtH
> launch

I came across this question: https://answers.launchpad.net/mg5amcnlo/+question/240257.
However, I could not find PS.input file or something similar. I also checked the FAQ and the check_sa.f file mentioned in there. I found the place with the comment 'write the information on the four momenta' but where exactly do I write the four momenta?
Thanks in advance!

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

in check-sa.f
you do have the following lines:
cc
cc Copy down here (or read in) the four momenta as a string.
cc
cc
c buff(1)=" 1 0.5630480E+04 0.0000000E+00 0.0000000E+00 0.5630480E+04"
c buff(2)=" 2 0.5630480E+04 0.0000000E+00 0.0000000E+00 -0.5630480E+04"
c buff(3)=" 3 0.5466073E+04 0.4443190E+03 0.2446331E+04 -0.4864732E+04"
c buff(4)=" 4 0.8785819E+03 -0.2533886E+03 0.2741971E+03 0.7759741E+03"
c buff(5)=" 5 0.4916306E+04 -0.1909305E+03 -0.2720528E+04 0.4088757E+04"
cc
cc Here the k,E,px,py,pz are read from the string into the momenta array.
cc k=1,2 : incoming
cc k=3,nexternal : outgoing
cc
c do i=1,nexternal
c read (buff(i),*) k, P(0,i),P(1,i),P(2,i),P(3,i)
c enddo
c
cc- print the momenta out
c
c do i=1,nexternal
c write (*,'(i2,1x,5e15.7)') i, P(0,i),P(1,i),P(2,i),P(3,i),
c .dsqrt(dabs(DOT(p(0,i),p(0,i))))
c enddo
c
c CALL SMATRIX(P,MATELEM)
c write (*,*) "-------------------------------------------------"
c write (*,*) "Matrix element = ", MATELEM, " GeV^",-(2*nexternal-8)
c write (*,*) "-------------------------------------------------"

you can uncomment those line, change the momenta in the first part obviously.
(and comment the previous computation of the amplitude if you care about that)

then you have to re-compile the code:
make check
and run
./check

Cheers,

Olivier

Revision history for this message
Steven Jeremies (minits) said :
#2

Thanks Olivier Mattelaer, that solved my question.