Comments for TAU-16-003 from DESY

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General comments:
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  Congratulations to the authors on a thorough and detailed paper comprehensively covering the new tau algorithm. In general the paper read well, with the exception of the introduction that could do with some redrafting. We also felt there was a lot of assumption that the 7,8TeV tau paper had already been read, when this wasn’t always necessary. More context could help to alleviate this issue. Some rephrasing in the introduction could solve this.

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Type A comments:
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Introduction general comment: don’t put commas before ‘and’ when it is used in lists.

lines 43-44: “The most important among these is the decay of Higgs bosons to pairs of tau leptons that constitute an especially sensitive channel to probe Higgs-to-fermion couplings of leptons” Rephrase -> “The most important among these is is the decay of Higgs bosons to pairs of tau leptons which constiute an especially sensitive channel to probe the coupling of the higgs boson to fermions” (or leptons, but not  ‘Higgs-to-fermion couplings of leptons, in which one of fermion or lepton is redundant). Would also caution against stating that H->tautau is the most important, I would say that is an opinion and probably doesn’t belong in the introduction.

line 45-56: “And, in fact, the observation of the SM Higgs boson decaying to a pair of tau leptons has recently been reported” -> “The observation of the SM Higgs boson decaying to a pair of tau leptons has recently been reported”

line 55: “In about one third of the time”->”About one third of the time”

line 69: better might be “… that there are fewer particles produced in tauh decays” (currently it reads as if the multiplicity is a property of the particles themselves”

line 72-73: “These features include” - > “The improvements include”

L104-105: silicon-pixel and silicon-strip (non-consistent use of "-")

line 137 “for an integrated luminosty of 35.9 fb-1” -> isn’t ‘corresponding to an integrated luminosity of …” better?

Line 146: ‘their’ -> ‘the’ or rephrase

line 147: Isn’t the preferred generator name MG5_aMC@NLO rather than MadGraph_aMCatNLO? . Furthermore: “are generated at LO using the NLO program…” this reads odd. How can you use an NLO program to generate events at LO? I know that the answer is you used the MadGraph5, ie LO part, of MadGraph5_aMC@NLO. Is it possible to drop ‘using the NLO program’?

Line 170: a->the particle flow ..

line 203: CSVv2, not CSV

line 207: redefinition of pTmiss? perhaps best to remove definition on line 171

line 211: previously tau_h has been referred to as tau_h decays, now it appears standalone. Should pick one and be consistent.

Table 1: do you need to include ‘rounded to the nearest…’, why don’t you use +/- symbol (as in the text) instead of just - in the table

L244: units for Rsig are unclear here, it is actually unitless no? The GeV units are on 3.0. It may be clearer to define Rsig with an equation.

L248: as well as -> and

L256: ‘from tau_h’ -> ‘from a tau_h’

L259: "despite that" -> "although" (?)

L310: can you clarify that the strip is per pi_0, at the minute it reads like it is per tau_h

line 318: isolation *region*?

line 337: “And therefore,...” ->”Therefore,…"

line 373: pedantic but shouldn’t the acronym be BDTs, such that you can talk about ‘a BDT’ later 

Fig 3: can you add curves as in Fig 2?

line 443-446: Too many commas in this sentence, please split it up. Also not grammatically correct: “the sample… which is dominated by X and Y events, corresponds to the most important source of e misidentified as tau_h, have electron pT…” - I guess corresponds  should be correspond (referring to X and Y) and ‘have electron pT’, ‘has electron pT’, to refer to the sample. Or ‘the MC sample’ should be ‘the MC samples’. 

line 502: “For events simulated through MC QCD multijet production” - > “For simulated QCD multijet events”

L617: events to -> events used to

L641: change the phrasing “Offline, …” this phrasing is used frequently and looks sloppy

line 697: “bin-by-bin uncertainty is jargon, perhaps ‘uncertainties due to the limited number of simulated events are taken into account following the barlow-beeston-light approach’ (even if it’s not properly barlow-beeston light…)

line 701: “The weights are meant to correct only … not the normalisation” -> “The reweighting corrects only the differential distribution, leaving the total normalisation intact” (or similar)

line 707: typo: measurementn->measurements

line 710-712: this would look better spelled out as ‘For the efficiency measurement at low pT between 20 and 60 GeV the mutau final state is used, etc. 

L720: why use the approx equals symbol in combination with ‘up to’, we’d recommend removing the symbol here and in other places

L736: ‘data-based’ is jargon

Section 9 general: the titles beginning ‘Using…’ don’t read very well on their own, can you rephrase them?e.g ‘Using the tag-and-probe method’-> ‘Measurement with the tag-and-probe method’

Table 7: at first glance the fact that these are % numbers is unclear, can you add % to the column titles? Additionally changing m_tauh -> sigma_{m_tauh} may make it even clearer

Fig 19: can you add a horizontal line at 1?

line 1230: “measured using 35.9 invfb of data” -> “a dataset corresponding to 35.9 invfb”

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Type B comments:
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Abstract:  This could be restructured to make it clearer that you are presenting a 13 TeV update of the algorithm, it first reads like you are reanalysing 7 and 8TeV data. It would be also nice if you could add numbers to show the degree of improvement for a representative working point

line 47: I don’t think you can have a sensitivity to a search. But searches with tau leptons in the final state can be sensitive to BSM models. 

line 47-48: “…for both neutral and charged MSSM higgs boson enhancements expected in the HIggs-to-tau couplings at large tanb, where tanb is…”. Probably better as “… for both neutral and charged Higgs bosons in the context of the MSSM.” The sentence as it currently stands is a bit tenuous (‘MSSM higgs boson enhancements’, what does that even mean? At high tanb the decay of A/H to tautau is enhanced wrt the SM decay value, but you don’t have space to write that and it also doesn’t matter)

line 51: Higgs bosons in the MSSM are also additional Higgs bosons. I suppose H->aa->xxtautau is meant, but why not just merge with the previous discussion of Higgs bosons in the MSSM and only say ‘additional Higgs bosons [2-8]? 

Line 117: there is no reference for the ECAL or HCAL

Line 195-196: it seems a bit strange that you use different PU correction for muons and electrons, you also need to mention the cone size used for the mu deltaBeta correction. It would be good if you mentioned the PU correction used for jets as well

line 231-233. Not clear what is mean there, it reads as if the pT requirement on the charged particles ensures corresponding track quality is good and that a minimum number of layers of the tracker has been passed. Is this genuinely what is meant, or are these three separate requirements that are all satisfied?

L253: this is the first mention of the isolation region? It may be worth briefly introducing it.

line 272: f and g are determined from simulation. Where any checks done to ensure these functions are also appropriate for data? 

L279: can you clarify where the upper and lower limits on the strip size numbers come from?

line 322: Does this mean there are two isolation variables that can be chosen by the user depending on the studied state, or is there one isolation variable that uses different DR cone sizes in case of different event properties?

L323: if the cut based is so much worse can you provide a justification for including it at all?

L336: it is unclear why the dBeta factor changed so much, we’d recommend getting rid of the mention of the previous factor

line 343-345 “Are chosen such that the resulting efficiencies for the three working points cover the range required for the analyses”: which analyses?, what are the ranges of efficiencies, what are the efficiencies of the working points?

line 378: “…such as…” are these all the variables that go in, or are there others that have not been mentioned? If the latter shouldn’t they be mentioned given that this paper is *the* documentation of the algorithm?

line 443-446: it is not clear why the tau_h identification and e->tau_h misidentification rate should be smaller around the peak of the training sample. Doesn’t this indicate a bias in the training?

line 701-704: “Uncertainties … no weights at all” - “Uncertainties in the reweighting are propagated by an uncertainty that varies between not applying the weight, and applying the weight twice”. Why is a 100% uncertainty applied? I remember other CMS tautau analyses which used Z pT and top pT reweighting derived dedicated uncertainties (for Z pT) or constrained the uncertainties in a ttbar control region (top pT). 

line 739: iirc there are non-negligible contributions from QCD multijet producion in this high mT control region in  other Run 2 di-tau analyses. How is this addressed in the case of the analysis presented here?

line 965: “In the measurement … backgrounds with true tau_h are subtracted” How is the measurement performed, using a likelihood fit to the data? Then this subtraction procedure will have introduced a systematic uncertainty on the data, how is this dealt with? Or is no fit performed and are all uncertainties externalised?

line 975: Is the uncertainty on e->tau_h fake rate genuinely 100%? From later on in the paper we do not get the impression that this is the case.

line 1014: Same comment as before, how do you deal with QCD multijet events that enter in the high-mT sideband? The sideband selection is also 10 GeV different from that in the mutau_h channel, is this reasonable?

Summary general: can you add representative numbers showing improvement here as well as in the abstract?

References: You only reference CMS, maybe you could include an ATLAS reference?