CMS TOP-18-003: CWR comments Roberval Walsh

Title
remove "standard model": we look into the production of 4 top quarks, then we test the SM hypothesis, not the other way around; we also look at new physics contributions in the paper

Abstract

L1-4: The production of four top quarks (tttt) at the LHC is studied using the data collected by the CMS detector in proton-proton collisions at the centre-of-mass energy of 13 TeV with an integrated luminosity of 137 fb-1 during the data taking period of 2016-2018.

L9-10: The two approaches are consistent with the next-to-leading order SM prediction.
(most important is that any method should be compared with what is expected)

L18-19: ...couplings to new light particles.
(To use 'lighter' must specify in comparison to what?)
(Also the whole sentence could be moved before mention to 2HDM because the new light particles arise from a modification of the EFT)

Introduction

L1: The production of four top quarks (tttt) is predicted by the standard model (SM) with a small cross section...

L5: The measurement of the tttt cross section ...

L7-8: Why the fact of having a small cross section makes it more sensitive to new physics? 

L10:  Is the heavy particle case also considered off-shell in addition to on-shell? If the contribution is negligible compared to the on-shell contribution then say so.

L11: remove "additionally" -> can be kept but is it additional in the sense that the new particles belong to the same models previously mentioned? It does not seem so. Does the off-shell model has a particular name? 

L15: remove "conversely"

L27-28: "Previous searches for tttt production in pp collisions at 13 TeV at the LHC were performed by the ATLAS[26,27] and CMS[28,29] Collaborations."

L28: remove "SM"

L34-41: The whole paragraph is not well written. What in the different running conditions improve the analysis? What does it mean "detector developments"? The larger luminosity itself is not explicitly mentioned as a source of improvement. Is the old cross section predicted really relevant?

L36-39: remove?


Background and signal simulation

L74-75: It is not clear how the samples for the scalar and vector off-shell contributions were generated


Event selection


L149: worth comparing the performances

L197: Why is CRZ the only control region for BDT?

L207: such algorithms -> because they...

Summary

L437: remove "standard model (SM)"

L445:
remove ", in agreement with ... [1]. The cut-based strategy yields" 
then add : Such strategy gives a better signal significance then the cut-based one that produces an observed... 

L448:
remove ", in agreement with the BDT result"
then add: The results of both strategies are in agreement with the standard model predicted NLO cross section of 12.0 +2.2 -2.5 fb [1].