Syntax for forcing two identical particles to different final states

Dear Prudhvi,
there are several different answers/aspects, depending what you want to do in detail. If you want to use the 'unstable' feature, then
you could define several different decay modes of the Z by explicitly defining things like
process zbb = Z => b, bbar
process zcc = Z => c, cbar
etc. and then do
unstable Z (zbb, zcc)
to have more than one decay. When you then generate events for the process e+ e- -> Z Z you will get a mixture of 4b, 4c, 2b2c final states according to the partial widths of the two decay processes. Alternatively, you could use the auto_decays feature described in Sec 5.8.2 of the manual.
For the unstable feature, full spin correlations are taken into account, however, the NWA (narrow-width approximation) is used, so you will not see a Breit-Wigner peak of your particle.
By using restrictions, you get the full propagator and hence the Breit-Wigner peak. In case you take electrons and muons as massless in the final state (which for energies of 200 GeV and beyond usually works well), you could have also used
process ee__ZZ_llbb = e1, E1 => e1:e2, E1:E2, b, B { $restrictions = "3 + 4 ~ Z && 5 + 6 ~ Z" }
instead of your example above. The splitting into two subprocesses is only necessary because of the different masses.
And yes, you can then apply cuts to restrict into the Z peak regions, either at the analysis level or already at the integration level by
using something like
cuts = all 85 GeV < M < 95 GeV [b, B] and all 85 GeV < M < 95 GeV [e1:e2, E1:E2]
Cheers,
    JRR (Juergen)

Note that the bug report linked here was done by erroneously, it was intended for the other issue,
https://answers.launchpad.net/whizard/+question/706411

Dear Juergen,

Thank you very much for your detailed answer. Using restrictions and cuts on invariant masses on lepton and jet pairs, I was able to generate events, for example, for e+ e- > Z Z with one on-shell Z -> l+ l- and the other on-shell Z -> b b~. However, in a scenario where two identical bosons in turn come from the decay of some new heavy particles, I'm not sure if I can still use restrictions. (Sorry if the following question is tangential to my initial question, in which case I'm happy to open a new question instead.) For concreteness, if I want to pair produce new heavy vectorlike quark "tp" (and its partner "tp~") that can decay to a Z boson and a (anti) top quark, I am trying to do:

        process ee_tptp = e-, e+ => tp, tp~

and then decay the (on-shell) tp's to Z and SM tops via

        process tp_Zt = tp => Z, t
        process tpbar_Ztbar = tp~ => Z, t~

and then use the "unstable" option for both tp and tp~ to force their decays. But, I'm not sure how to proceed further if I want one of the on-shell Z's to decay to b b~ and the other Z to mu- mu+;

        process Z_bb = Z => b, b~
        process Z_mumu = Z => mu- mu+

and only generate a sample with (2b, 2mu, and 2t) in the final state but not (4b, 2t) or (4mu, 2t)? So I was wondering if there is a syntax to achieve this? (And there seems to be no issue in generating a sample with 4b's or 4mu's in the final state if I simply use the unstable option for Z to force it to decay to b b~ or mu- mu+.)

Following were some of my unsuccessful attempts:

-> use "unstable" option for Z, unstable Z (Z_bb, Z_mumu), but this also generates samples of (4b, 2t) and (4mu, 2t) in addition to (2n, 2mu, 2t)

-> use restrictions in the decay of tp and tp~, by modifying the process tp_Zt and tpbar_Ztbar:

        process tp_Zt = tp => b, b~, t { $restrictions = "3 + 4 ~ Z"}
        process tpbar_Ztbar = tp~ => mu-, mu+, t~ { $restrictions = "3 + 4 ~ Z"}

and impose cuts on b b~ and mu- mu+ such that their invariant masses are around the Z pole. However, due to the absence of vertices of tp with (b, b~, t) or (mu-, mu+, t) the process seems to fail.

Please let me know if there are any suggestions on how to achieve this.

Thank you very much,
Prudhvi

Hi Prudhvi,
just a quick comment (Thorsten has spotted this actually): in this example of yours, the counting is wrong:
       process tp_Zt = tp => b, b~, t { $restrictions = "3 + 4 ~ Z"}
        process tpbar_Ztbar = tp~ => mu-, mu+, t~ { $restrictions = "3 + 4 ~ Z"}
There is only initial particle 1, and the final state particles are 2,3,4, respectively. So the restriction should read:
       process tp_Zt = tp => b, b~, t { $restrictions = "2 + 3 ~ Z"}
        process tpbar_Ztbar = tp~ => mu-, mu+, t~ { $restrictions = "2 + 3 ~ Z"}
Regarding the different decay modes from identical final state resonances, I need to think a bit about it: probably you can do a flavor selection on the final state, but we have to try this out first.
Cheers,
    JRR

Thanks Juergen Reuter, that solved my question.