Calculating amplitude in python
Hi,
I followed https:/
1) I get the same result as the example, however after using some different momentum, like
p = np.array([[ 53.35411266, 0. , 0. , 53.35411266],
[ 1146.1299388 , -0. , -0. , -1146.1299388 ],
[ 261.02808531, -70.24765479, 58.6271451 , -196.95877203],
[ 938.45596613, 70.24765479, -58.6271451 , -895.81705408]])
The result "ans" is 0.0. This four momentum is from the lhe file of a pp->tt process.
The zero result occurs for around half of the events for a 1 million event lhe file.
Why the result is 0?
2)nhel = -1 # means sum over all helicity
In the code the nhel is defined as above. Does it sum over the inital plus final state particle, or only final state particles?
3)
In the matrix.f file,
IF (NHEL.NE.0) THEN
CALL M0_SMATRIXHEL(P, NHEL, ANS)
ELSE
CALL M0_SMATRIX(P, ANS)
And in the subroutine M0_SMATRIXHEL,
USERHEL=HEL
CALL M0_SMATRIX(P,ANS)
USERHEL=-1
And in the subroutine M0_SMATRIX
DATA USERHEL/-1/
What does "DATA USERHEL/-1/" means? Is it a selection of the amplitude from the following:
DATA (NHEL(I, 1),I=1,4) /-1,-1,-1, 1/
DATA (NHEL(I, 2),I=1,4) /-1,-1,-1,-1/
DATA (NHEL(I, 3),I=1,4) /-1,-1, 1, 1/
DATA (NHEL(I, 4),I=1,4) /-1,-1, 1,-1/
DATA (NHEL(I, 5),I=1,4) /-1, 1,-1, 1/
DATA (NHEL(I, 6),I=1,4) /-1, 1,-1,-1/
DATA (NHEL(I, 7),I=1,4) /-1, 1, 1, 1/
DATA (NHEL(I, 8),I=1,4) /-1, 1, 1,-1/
DATA (NHEL(I, 9),I=1,4) / 1,-1,-1, 1/
DATA (NHEL(I, 10),I=1,4) / 1,-1,-1,-1/
DATA (NHEL(I, 11),I=1,4) / 1,-1, 1, 1/
DATA (NHEL(I, 12),I=1,4) / 1,-1, 1,-1/
DATA (NHEL(I, 13),I=1,4) / 1, 1,-1, 1/
DATA (NHEL(I, 14),I=1,4) / 1, 1,-1,-1/
DATA (NHEL(I, 15),I=1,4) / 1, 1, 1, 1/
DATA (NHEL(I, 16),I=1,4) / 1, 1, 1,-1/
DATA IDEN/256/
4) In DATA IDEN/256/, why is it 256 but not 16?
Thank you!
Best,
Li
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