Dear editors

We have read the paper in the "institutional review" of the DESY CMS group. 
The article is very interesting, but not easy understandable for the non experts. It could make the article more readable, if the long sections were structured with subsections.

Please find our detailed comments below

Good luck for the next steps

DESY CMS group

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General comments:
Too many plots at the end, are all necessary for the paper?
Chapter1 (Introduction) and Chapter4 (Event reconstruction and object identification)  maybe could  be better structured and shorted.

Type A comments:
- general: maybe avoid splitting equations over lines (use "~")

L11:     "N" is never defined explicitly

L47-49: Second part of the sentence does not seem grammatically correct. Either state 
            “the right two diagrams show ….”, or end the previous sentence at the comma and
             start a new sentence “The right two diagrams do not add to the Wg fusion and are 
             small QED corrections”

L68:      “and the corresponding cross section is twice as large as the cross section of the 
             dimuon and dielectron channels” (or similar - in any case the cross section cannot 
             be twice as large as another channel)

L70-73: this is a very long sentence with many commas. Consider splitting this up 
             for readability.

L70-73: is 8TeV analysis more recent than 13TeV?

L82-83: “…that is consistent with a W(qq) decay products merged in a single jet” -> 
             “… that is consistent with a W(qq) decay where the decay products are merged in 
             a single jet” (or similar)

L85:     Avoid comments in brackets, why not simply make this statement as a separate 
            sentence?

L137-138: use \texttt or \textit for names of PDF sets

L298:   Can the comment in brackets be incorporated in the sentence? in any case ‘the 
            results using a=4 were found to give the consistent results’ should be something 
            like ‘Consistent results were found when using a=4’

Ref 8:   SU, not su (capital)

Type B comments:
Abstract:
 "Upper limits are set, in the context of a Type I seesaw mechanism, on the cross section times branching fraction for production of a heavy Majorana neutrino in the mass range between 20 and 1600 GeV. “ only upper limits on the mixing matrix elements are quoted in the results section, so perhaps drop the comment that limits are set on xs x BR?

Chapter 1: Introduction. 
L2-3     Add reference in the first sentence (at least two of the SM neutrinos has mass)

L7-8     explain for the sentence on Dirac mass model

L20      Question: is there a connection on type I seesaw mechanism and the limit on the mass of 
            the neutrino partner. If yes, maybe explain a bit there. Is it the analysis restricted to that 
            limit of the model, or is it broader? 

L45:    The text states “ in this study… is considered”. Is this in addition to the process 
           depicted in Fig 2, or does Fig 2 have nothing to do with the state that is probed 
           with this analysis? 

L47      "considered" -> "additionally considered" since the Fig 2 is also considered ?

L52       Maybe explain why both opposite and same-sign lepton pairs can be produced in 
             Majorana neutrinos theory

L68       cross section or branching ratio, better?

L91       contradiction with L276, two jets -> at least two jets, a large-cone jet -> at least one 
             large-cone jet

Figure 2:  is there a DY s-channel?

Chapter 2 CMS Detector
General comment: is not better to use standard version of CMS detector description?

Chapter 3: Data samples and simulations

L127:     NNPDF3.0 is not the standard way to cite the PDF

L125      Does not Powheg also include gg->ZZ? why is used MCFM for that?

Chapter 4: Event reconstruction and object selection

L152       jet finding algorithm -> jet clustering AntiKT algorithm

L213       Formula: DeltaR>mjet/pt -----> DeltaR>2*mjet/pt ? (are considered boosted objects 
               when the pt is larger than twice the mass) 

L234-238: 1) "medium working point" -> this is slang, not needed, also since it is explained in 
                the last sentence; you could simply rephrase "the identification is performed with the 
               CSVv2 algorithm [ref]". 
                 2) CSVv2 relies on many more properties; suggest: "This algorithms relies on many 
                discriminating variables, such as ..." 
                 3) Values for efficiency and misidentification probability of 63 and 1% are true for 
                *pt > 30 GeV* (but actually the performance decreases very significantly at higher pt)

L251        triggers legs (CMS slang)

L265-271 add the fact of two kinematics options are considered for each region (low mass and 
                higher mass), and also add the explanation why is only possible use boosted regime at 
                the higher mass region

Chapter5: Background estimation 

L318        add the fact that should be "charged" leptons 

L451-L456 Maybe is better to call these CR "validation CR" since there were defined another CR 
                for the normalization

L344      call it here validation region, since you later use control region

L 348-349: This reads as if the fit in the CR was performed independently of the SR fits later on. 
                Is this the case? If not please make it clear that a simultaneous fit of CR and SRs was
                performed. If this is not the case, why was the CR not included in a simultaneous fit with 
                the SRs?

L 350-356: same comment as above, why not include the CR in a simultaneous fit with the SRs? 
                If we trust the control region is defined correctly, we should be able to trust the constraint
                from the fit there and do not need to apply uncertainties on the simulated sample cross 
                section. In addition, if a correction is in order then that correction needs to be applied, 
                one cannot simply assign an uncertainty. Is there a reason the correction was not applied?

L384        inexact model of the parton showering processes?. Remove "inexact" it is just the fact t
                hat is a model.

L406        It is not clear,  what is meant by ‘MC simulation CRs in data’ - would it be possible to 
                clarify this? 

Chapter6: Systematics Uncertainties

L492        An 88% uncertainty is very large. How come it is so large?

L 502-505: by stating that the uncertainty of 50% is conservative, the impression is given that 
                the number of 50% is not well-motivated. Can a better motivation be given for this large
                uncertainty?

L508        is it just 11- 18 % and 16 - 43 % ?

L518        Clarify the fact that the PDF uncertainties are included in the normalization 

L530        what is the normalization uncertainty here, and why is the df uncertainty not accounted for ?

Chapter7: Results

figs 6-7:    Maybe it should be made clearer that a specific optimization is performed for each 
                 mass point, and that therefore the observed yields can vary within what is labelled the 
                 same SR. This confused us for a while. Clarify that it is not an spectra which can be 
                 varied the bin size in order to increase statistics ie: Fig7. 

Table5      In the "High-mass SR2" column  "misid bkg" the  same systematics  and statistics 
                  uncertainties? it is by chance?

Chapter 8: Summary
Maybe clarify the limits of the "seesaw mechanism" and the limits of the analysis, is not clear the matching of that from the introduction and the analysis itself