view process or display diagrams

Hi Yehia,
the option you are looking for is ?vis_diags = true. If this is activated, WHIZARD will generate a PDF file containing the contributing diagrams (c.f. the WHIZARD manual [1], p. 357).

Best regards,
Pascal

[1] https://whizard.hepforge.org/manual.pdf

For a decay process like :
process e1,E1 => Z, Z {?vis_diags = true}
process Zdec = Z => e2, E2 {?vis_diags = true}
unstable Z(Zdec)

The ouptut is two separate diagrams for the main process and the subsequent decay like a diagram for e-,e+ > Z, Z and another separate diagram for Z > mu+ mu-. How can I get them into one diagram?

Yes, the diagrams represent exactly the processes that are calculated. A process definition like

process e1,E1 => Z, Z {?vis_diags = true}
process Zdec = Z => e2, E2 {?vis_diags = true}
unstable Z(Zdec)

will produce two on-shell Z bosons which subsequently decay to muons and this is represented by the generated diagrams.

If you want to compute the process e+ e- -> μ+ μ- with all possible mediators, you can simply specify

?vis_diags = true
process e1, E1 => e2, E2 , e2, E2

However, this will also take into account photon propagators. If this is undesired, you can restrict the processes O'Mega takes into account for the matrix elements by defining restrictions (c.f. manual, sec. 5.4.3).
To disable the photons,

?vis_diags = true
process e1, E1 => e2, E2, e2, E2 { $restrictions = "!A" }

would to the trick. In this case, the Z bosons will not be produced on-shell. Using restrictions, you can also specify that two specific external particles should come from a specific intermediate particle, e.g. $restrictions = "3+4~Z".

Best regards,
Pascal

Thank you Pascal
But for a process like e+ e- > t tbar (t -> b W+ , W+ > mu+ vm). If I write this as
e1, E1 => b, bbar, e2, E2

How can I restrict the W boson and the bottom quark to come from a top quark while the top is not given as an input?

Hi Yehia,
please take a look at share/tests/functional_tests/user_prc_threshold.sin. If you have a process
e1, E1 => tbar. b, E2, numu
the restrictions look like this:
e1, E1 => tbar. b, E2, numu { $restrictions = "4+5+6 ~ t" }
or, if you like, also { $restrictions = "5+6 ~ W+ && 4+5+6 ~ t" }
Cheers,
   JRR (Juergen)

Thank you Juergen, this helped a lot.

I can now get the feynman diagrams that I want but there is another small issue. The intermediate state particles don't show up in the output lhe file neither do the mediators. I can only see the initial and final state particles. Take this as an example:

===========================================================
?vis_diags=true
process eeTozz = e1, E1 => e2, E2, e2, E2 {$restrictions = "3+4~Z && 5+6~Z"}
compile

beams = "e1", "E1" => circe2
$crice2_file = "ilc500.crice"
$circe2_design = "ILC"
$circe2_polarized = false

beams_pol_density= @(-1), @(+1)
beams_pol_fraction= 80% , 30%

sqrts = 500 GeV

integrate(eeTozz)

$sample = "eeTozz"
sample_format = lhef

simulate(eeTozz){n_events=5000}
show(results)
========================================================

The output lhe file looks like this

=====================================================

<init>
 11 -11 2.5000000000E+02 2.5000000000E+02 -1 -1 -1 -1 3 1
  4.4309448324E-04 1.6983579909E-06 1.0000000000E+00 1
<generator version="3.1.1">WHIZARD</generator>
<xsecinfo neve="5000" totxsec="4.4309448324E-04" />
</init>
<event>
 6 1 1.0000000000E+00 4.9979285312E+02 -1.0000000000E+00 1.1780000000E-01

 11 -1 0 0 0 0 0.0000000000E+00 0.0000000000E+00 2.4990437795E+02 2.4990437795E+02 5.1099700000E-04 0.0000000000E+00 9.0000000000E+00

 -11 -1 0 0 0 0 0.0000000000E+00 0.0000000000E+00 -2.4988847543E+02 2.4988847543E+02 5.1099700000E-04 0.0000000000E+00 9.0000000000E+00

 13 1 1 2 0 0 -1.6579811549E+01 1.8133219786E+02 -9.7415874649E+01 2.0650937008E+02 1.0565838900E-01 0.0000000000E+00 9.0000000000E+00

 -13 1 1 2 0 0 -3.9742100384E+01 2.0594804863E+01 -3.6869538541E-01 4.4763016322E+01 1.0565838900E-01 0.0000000000E+00 9.0000000000E+00

 13 1 1 2 0 0 4.0935459964E+01 -1.6239794172E+02 1.1456065603E+02 2.0291120825E+02 1.0565838900E-01 0.0000000000E+00 9.0000000000E+00

 -13 1 1 2 0 0 1.5386451970E+01 -3.9529061001E+01 -1.6760183484E+01 4.5609258731E+01 1.0565838900E-01 0.0000000000E+00 9.0000000000E+00

<weight name="sqme_prc">9.7413270042E-09</weight>
</event>
<event>
============================================================================

Thanks Juergen Reuter, that solved my question.