Thanks for this contribution and sorry for this late comment. My life is a bit hectic at the moment, as the deadline for a big grant proposal is approaching (and the application takes most my time). Typical academic life, somehow… ;)

And thank you! I really do appreciate how much time and effort you put into reviewing and commenting on these posts. The effort is clear. Especially given you don't have a lot of time with your grant proposal deadline looming.

I hope the grant proposal goes well. :)

As mentioned in the references you quoted, the (very large amount of) energy associated with each produced top quark is shared between its decay products. Some part goes to the W boson and some part to the b quark. Calculations tell us how the energy-momentum is shared in detail, and I won’t do them here (because it is not needed to qualitatively understand what is happening in our collisions). In most cases, the b quark gets a momentum larger than 25 GeV because the produced top quarks are so massive that we have a big reservoir of energy to be shared between the decay products (as you mentioned).

Yes! The energy associated with each top quark is shared with it's decay products. Great to know that the decay process itself is the primary avenue in which the byproducts are granted their energy. I was initially stuck in my thinking regarding the momentum of the protons in the beam.

You should not do this addition. As we plot distributions, we don’t know if a configuration corresponding to the peak of the lepton PT is that corresponding to the peak of the MET, and so on. We observe that the order of magnitude of the three peaks is similar, which is what is expected as we can see our top quarks as particles decaying into three other roughly massless particles. Consequently, the energy can be seen as split in three, in a first-order approximation.

Ahhh! You pointed out the magnitude of the peaks in your post. This explanation clears up my thinking on why the graph of MET is justified.

Can you explain to me where the second neutrino would come from? I didn’t get this. I guess you just had luck here. As soon as we selected events containing a single lepton, then we have a single neutrino. A second neutrino must always come together with a second lepton. Note that it is possible that we have two leptons, and that one of the leptons is lost. This however does not represent the majority of our events.

Yeah, I kept thinking about this after-the-fact and posted a comment on the second neutrino:

After some thought, I don't think I had justification for concluding that there are two neutrino emissions. After all, we only selected for the emission of one lepton. I think there would be 2 leptons if there were two neutrinos (each W boson decaying into 1 lepton and 1 neutrino). I'm guessing it's likely that there's only one neutrino, which means I need to think more deeply about the missing transverse energy.

And you already answered the question I had regarding the neutrino only showing up alongside a second lepton :) In all, it came down to my unexamined thinking that the decay products of the top quark would be symmetrical. I realized my error upon digging deeper into the top quark decay products. It's clear, even in the top-quark decay products diagram I linked to, that a neutrino may not necessarily appear as a byproduct of top quark decay.