Generation of TTZZ sample without MadSpin card

[G-Vian]

Dear GEN team,

My team wants a ttZZ sample with 13.6 TeV center of mass energy. The other TTZZ card, available at [1], contains a MadSpin Card that decays the ZZ, that's why I created these cards for a TTZZ process without Z decaying.
Thank you very much.

[bbilin]

Thanks. I think the tops need to be decayed in the Madgraph. (or madspin)

[G-Vian]

Dear Bugra,

I didn't request the top's decay, as my team wants this sample with the top decaying inclusive.
Thank you very much!

[lviliani]

Dear @G-Vian, in this case the decays will be handled by pythia8, which does not take into account spin correlations effects in the decays. This will lead to wrong distributions for spin sensitive observables.
If you want inclusive decays, the best way is still to use Madgraph or Madspin to handle them.

[G-Vian]

Dear Lorenzo,
Thanks for your prompt answer.
I modified the proc card, adding the decay of the tops.

[lviliani]

Dear @G-Vian , thanks for following up and sorry for the late response.
I think it would be even better to include the full decay chain, i.e. also the W decays.

But actually, referring also to the other TTZZ card that you mentioned at the beginning, what is the difference here? It looks to me that in both cases you will get inclusive decays.

[G-Vian]

Dear Lorenzo,
We would like to keep the W undecayed because we want to explore different channels from these decays.
Additionally, the previous TTZZ card had a MadSpin Card that decays the ZZ, which was undesirable.

[lviliani]

Sorry, I'm not following.
In the previous TTZZ card you are decaying top and Z to all, which means they are inclusive in the decays and your samples will contain all the decay channels.
Now, if you don't decay Z and top in madgraph/madspin, it will be decayed later on by Pythia8 to all possible channels, so you will get an inclusive sample anyway.

[G-Vian]

Yes, thats correct.

[lviliani]

Ok thanks, then I don't understand why you need these new TTZZ cards.

[G-Vian]

It is because we dont want the MadSpin decay of the Zs

[sihyunjeon]

But then why decay top in madgraph?

Setup is not superbly convincing

Either you drop all the decays in madgraph/madspin to enhance computing performance (pythia is faster) OR decay both t and z

You decay top down to w and b. Why? Pythia decays top to w and b anyways

You can do
decay z > all all
If you want inclusive z decays

Or are we missing sth here

[G-Vian]

I have decayed the Tops because was informed in the previous comment that leaving it to Pythia decay would lead to wrong spin correlations.

[sihyunjeon]

Same story goes for z, it loses spin correlation when pythia handles it

[lviliani]

To me the proper configuration is the previous one, in which you use madspin for all the decays.

Maybe if you explain why you don't want madspin we can have a better understanding.

[G-Vian]

Dear GEN conveners,

I apologize for the delay in responding, but I have discussed this with my analysis team, and they have concluded that we will perform all decays in Pythia. We will do this in the same way as it was done in our analysis of Run 2.

Thank you very much, and please forgive the delay.

[G-Vian]

Dear GEN Conveners,

I have also added cards for the TTZH process for Run 3, as the cards from this link [1] for Run 3 had a BW Cutoff value of 15000.

[lviliani]

Hi @G-Vian, the recommendation from GEN is to use Madgraph or Madspin for the decays, and not Pythia8 because the spin correlations are lost in this case. As we wrote previously, using Pythia8 will lead to wrong kinematic distributions for variables sensitive to spin correlations.

[G-Vian]

Dear Lorenzo, we are aware of this problem, but we still want to follow this approach. We want to do this in the same way as it was done in our analysis of Run 2.

[lviliani]

Hi @G-Vian, before merging this PR, we would like to ask you or your team to present at one of the upcoming GEN meetings (Mondays at 2pm) to discuss whether this approach is sensible in your analysis.
Please get in touch with us via email or mattermost to organize the presentation.
Thanks!

[G-Vian]

Dear GEN conveners,

Following your message, we decided to perform the decays of the Z boson and the top quark in MadGraph (or in a MadSpin card) to preserve spin correlations. Initially, we planned to handle the decays in Pythia, during the event generation, following what was done in the generation of these processes for Run 2.

With this in mind, we are thus considering modifying the other cards we submitted for Run 3 (i.e. for TTZH, TTHH and TT4b), to be consistent with the prescription of performing the decays through MadGraph (or MadSpin). The tops (inclusive) and Zs (Z > bb~) will be decayed following this new prescription, except for the Higgs, which will be decayed in Pythia (H > bb~).

G. Vian, A. Savoy-Navarro, W. Wei