MadGraph5_aMC@NLO

There is no particle data I need in the lhe file

Asked by Zongyang LU

I generated the mu+ mu- > z | zp > t t~,(t > w+ b, w+ > e+ ve),(t~ > w- b~,w- > e- ve~)process. In the lhe file, I can see the particle data of particles mu+mu - t~w+w - e+e - ve ve~and b, but I can't find the particle data of Z and Zp. How to operate if I want to find the data of particle zp or z.

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Olivier Mattelaer
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Zongyang LU (zongyang) said : 		#1

This is part of the lhe file.
<iteam>
<event>
12 1 +1.1717700e-03 5.00000000e+02 7.81860800e-03 9.39981000e-02
-13 -1 0 0 0 0 +0.0000000000e+00 +0.0000000000e+00 +2.5000000000e+02 2.5000000000e+02 0.0000000000e+00 0.0000e+00 1.0000e+00
13 -1 0 0 0 0 -0.0000000000e+00 -0.0000000000e+00 -2.5000000000e+02 2.5000000000e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
6 2 1 2 501 0 -1.6978450578e+02 -3.0412296184e-01 -5.9228861634e+01 2.4924241526e+02 1.7258868046e+02 0.0000e+00 0.0000e+00
24 2 3 3 0 0 -7.2706927803e+01 -5.7946893559e+01 +1.7327925202e+00 1.2084787323e+02 7.7182032042e+01 0.0000e+00 0.0000e+00
-6 2 1 2 0 501 +1.6978450578e+02 +3.0412296184e-01 +5.9228861634e+01 2.5075758474e+02 1.7476966945e+02 0.0000e+00 0.0000e+00
-24 2 5 5 0 0 +2.3253181961e+01 +1.6253832370e+01 +5.7931380049e+01 1.0328014393e+02 8.0658823429e+01 0.0000e+00 0.0000e+00
-11 1 4 4 0 0 -1.2157058517e+01 -8.5642337489e-01 +3.0461029358e+01 3.2808563552e+01 0.0000000000e+00 0.0000e+00 1.0000e+00
12 1 4 4 0 0 -6.0549869287e+01 -5.7090470184e+01 -2.8728236838e+01 8.8039309677e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
5 1 3 3 501 0 -9.7077577974e+01 +5.7642770597e+01 -6.0961654154e+01 1.2839454204e+02 4.7000000000e+00 0.0000e+00 -1.0000e+00
11 1 6 6 0 0 +9.8473518153e+00 -3.1865343380e+01 +3.4901747201e+01 4.8275277360e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
-12 1 6 6 0 0 +1.3405830146e+01 +4.8119175750e+01 +2.3029632848e+01 5.5004866565e+01 0.0000000000e+00 0.0000e+00 1.0000e+00
-5 1 5 5 0 501 +1.4653132382e+02 -1.5949709408e+01 +1.2974815845e+00 1.4747744081e+02 4.7000000000e+00 0.0000e+00 1.0000e+00
</event>

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Olivier Mattelaer (olivier-mattelaer) said : 		#2

Olivier Mattelaer suggests this article as an answer to your question:
FAQ #2173: “Intermediate Boson missing from events in LHE output file”.

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Zongyang LU (zongyang) said : 		#3

Thank you for answering my question. Does this mean that modifying the value of bwcutoff allows particles not on- shell to be written to the lhe file without affecting other results.

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Best Olivier Mattelaer (olivier-mattelaer) said : 		#4

With the syntax that you use (the decay chain syntax or the comma symtax).
You do request the top and W to be onshell, which "onshell" also follow the bwcut parameter.
Increasing the parameter will therefore also includes off-shell effects for the top/W but since the phase-space integrator assumes that your top/W are in the narrow width approximation, this can leads to efficiency/bias issue.

So no you can not increase to large value bwcutoff.
Additionally, at some point writting a Z or Zp inside the lhef file is kind of meaningless since you also have the interference term.
If you run your events with parton-shower, the inclusion of those offshell Z/ZP will also bias your parton-shower which is also bad.

Cheers,

Olivier

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Zongyang LU (zongyang) said : 		#5

Thanks Olivier Mattelaer, that solved my question.

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Zongyang LU (zongyang) said : 		#6

I understand. Thank you for your detailed answer.

genuine,

Lu