Difference: BFrancisNotes (7 vs. 8)

Revision 82016-01-04 - BrianFrancis

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META TOPICPARENT name="BrianFrancis"

SUS-15-009: Search for natural GMSB in events with top quark pairs and photons (8 TeV)

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For the GGM comment I agree, however in small points in your suggestion I would disagree. I feel it's best to keep the language of "lightest squark or gluino" versus just "lightest squark". The stop being much lighter than the gluino is important to the analysis, otherwise any allowed gluino production would be very close to those in the inclusive photon searches (ie no third-generation decays) we've published previously. "Squark or gluino" is a bit confusing I accept, so if there are any recommendations how to clean this up while retaining the gluino caveat I'd be happy to change it.
I also prefer the language of "top squark" over "stop quark" for clarity that it is not a quark. Somewhere else a comment was made that "stop squark" is redundant so I have edited those instances to be "top squark". The updated Figure 1 caption now reads:
"Feynman diagram of the GMSB scenario of interest. With top squarks as the lightest squark or gluino, their pair production would be the dominant production mechanism for SUSY in pp collisions at the LHC. Assuming a bino-like neutralino NLSP, each stop would decay to a top quark and a neutralino, with the neutralino decaying primarily to a photon and gravitino. Shown above the the electron~+~jets or muon~+~jets final state of the top pair decay."
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Prefer to call them "top squarks" as they are not quarks. Rewritten as:
"Feynman diagram of the GMSB scenario of interest. With top squarks (stops) as the lightest squark, the pair production of stops would be the dominant production mechanism for SUSY in pp collisions at the LHC. Assuming a bino-like neutralino NLSP, each stop would decay to a top quark and a neutralino, with the neutralino decaying primarily to a photon and gravitino. Shown above the the electron~+~jets or muon~+~jets final state of the top pair decay."
 
  • l 6: what is "a new little Hierarchy problem"? How does it differ from the known 'regular' hierarchy problem? Can you explain or give a reference?
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If you recall the diphoton inclusive MET search (gamma gamma + X), the MET resolution is very different for events with 'fake' photons (really jets). What this sentence should convey is that if you also have a semileptonic ttbar decay in the event, the effect of a poorly-reconstructed photon is pretty small compared to all the other activity in the event. I've re-written this section to read:
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If you recall the diphoton inclusive MET search (gamma gamma + X), the MET resolution is very different for events with 'fake' photons (really jets). What this sentence should convey is that if you also have a semileptonic ttbar decay in the event, the effect of the reduced energy resolution for one object on the total MET is pretty small compared to all the other activity in the event. I've re-written this section to read:
  "The control region definition is chosen to be orthogonal to the signal regions, to have very low signal acceptance, and to greatly
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Anthony Barker on PAS v0:

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  • Abstract:
just lightest squark, not squark/gluino.
Include a statement in the abstract about what limit you set.

Done.

  • Figure 1:
The first line of text in the body of the paper involves an undefined acronym: GMM. In fact, GMM is not explained anywhere in the paper. Please define GMM.
Second sentence starts with a preposition and has no verb. "With stop squarks...
"Assuming a very bino-like neutralino NLSP" is a caveat better put in the introduction than in the figure.
"Shown above is.." Should be the words starting the figure caption, not the start of the 4th sentence.
Please cleaning up the grammar and flow of this caption.

GMM is removed.
I'm no expert in grammar, but isn't "with x as y" here a dependant clause modifying "production would be the ..."? "would be" should be the predicate.
The "bino-like" comment appears in both the caption and the introduction (line 11-12), as it should to keep the caption self-explanatory.
All captions begin with just a statement of what the object is, rather than "Shown here...".
Caption now reads:
"Feynman diagram of the GMSB scenario of interest. With top squarks (stops) as the lightest squark, the pair production of stops would be the dominant production mechanism for SUSY in pp collisions at the LHC. Assuming a bino-like neutralino NLSP, each stop would decay to a top quark and a neutralino, with the neutralino decaying primarily to a photon and gravitino. Shown above is the electron~+~jets or muon~+~jets final state of the top pair decay."

  • Introduction:
line 4: use double quotes on "natural".

Done.

line 6, If "little higherarchy problem" is meant to be a proper name, capitalize "Little".

Made all lower case to match other CMS papers.

line 8 should say "motivated by models of Gauge-Mediates Symmetry Breaking". GMSB is not a single model. Also change the next clause accordingly.

Done.

line 9: neutralino NLSP is not the only case in GMSB (See http://arxiv.org/pdf/hep-ph/9801271v2.pdf pg 36) Maybe you mean to say "...we describe a GMSB motivated model in which the neutralino is ..."

Agree, changed to be your suggestion.

line 12 awkward sentence. Suggestion: "...neutralino case whose dominant decay, x->yG, produces a photon in the final state."

Now reads: "This search considers the case of a very bino-like neutralino, where photons in the final state would originate from its dominant $\chiz_1 \rightarrow \gamma \tilde{G}$ decay."

line 13: get rid of the word the in "conserved, the pair-production"

Done.

line 19: The second clause lacks a subject; should be "and it defines"
The sentence on lines 18-20 should be split into two sentences. This sentence is also confusing due to the word "isolate". At this point it is unclear whether the analysis is simply requiring a lepton that is assumed to come from tt or whether it is able to identify that the lepton came from the tt system rather than from qcd or gjet. Then it's ambiguous how many photon categories are there? Is it two categories: 1 or 2+? Or is it three categories: 1, 2, more than 2?
line 21: they're not "poorly isolated". You didn't do a bad job of isolating them, as though isolation were some active process that you could mess up. They are loosely isolated photons with tight photons excluded. This sentence has two totally unrelated things going on. Split it in to two sentences at the comma.

Cleaned up considerably. Removed mention of 'poorly isolated' in favor of 'photons that fail the nominal requirements...'.

line 28: you mean in *this" GGM scenario.

"This" GGM scenario isn't defined until later, and "a GGM scenario" is not incorrect.

  • Section 3
 
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line 59: "anti-kt" not "antikt" (Example: http://arxiv.org/pdf/0802.1189.pdf)

Fixed.

  • Section 4:

line 104-105 the term "electromagnetically fluctuated jets" is needlessly opaque and will only be understood by other photon experts. Maybe say "jets that hadronized predominantly to electromagnetic objects", "Jets with a predominantly electromagnetic final state", or something that can be understood by a generic physicist. Also, say here that these type of objects are "photon-like jets" so that the term can be understood on line 109.
Something line 104-105 should read something like "These objects, which we will refer to as photon-like jets, are dominantly jets that hadronized predominantly to electromagnetic objects"

Now "These objects are predominantly jets with large electromagnetic fluctuations in their hadronization and are used..."

line 110-111: This sentence makes no sense. I don't even have a good guess of what it's attempting to communicate. What effect of the tt system on met resolution do you have in mind? As in, what tt-free baseline are you comparing this to? Why does it make sense to compare met resolution and photon resolution. Which photon resolution are you tailing about? Energy resolution? Of one photon or both? Or do you mean the contribution of the photon energy mis-measurement on met? What sort of highlighting are you talking about and why would you ever want to? Which control region selection? The definition of fake photons or the boundaries of the two control regions? The same confusion occurs in the caption of Table 2.

This section has been rewritten in response to Manfred's comment. My comment to him:
"If you recall the diphoton inclusive MET search (gamma gamma + X), the MET resolution is very different for events with 'fake' photons (really jets). What this sentence should convey is that if you also have a semileptonic ttbar decay in the event, the effect of the reduced energy resolution for one object on the total MET is pretty small compared to all the other activity in the event."

line 113: many photons? in the tt+gamma case it's 0, and you see no more than 2 photons. So "many" is 0,1, or 2.

"Many" here refers to all selected photons from all background events. I've added the word "selected" to clarify. For example in the electron SR1 channel, you still expect 901 (many) ttbar + jet events as having one reconstructed, selected photon.

line 116: I don't know what a 2-7 configuration is. Please add a reference to explain that.

This is only a configuration of MadGraph and will not have a reference; the (pp \rightarrow bbjj\ell\nu\gamma) should be the explanation.

line 127: It seems you are using the Z to ee resonance to understand the electron to photon fake rate. This sentence hints at that, but there is no mention of the Z. Please make it explicit.

Done.

line 131: second clause has no subject. Add the word "it": "and it is formed..." or break into two sentences.

Rewritten extensively from a comment by Manfred.

Table 1: please reference the column headers SF_Z(g) and SF_e->g in the preceding paragraph and in the caption.

Done.

Table 1 caption last sentence: Please make this a proper sentence rather than short-hand. Also use the word "uncertainties" rather than "errors": "The shown uncertainties include only the statistical uncertainty and the uncertainty in the integrals of the fits."

Typographical error, this should be "only the first one is applied". Fixed.

Figure 2 caption: say "uncertainty" not "error".**Also, mention that the e-gamma plot is the plot on the right.

Done.

 
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Figure 4: use larger fonts. Make the horizontal axis read Et^miss instead of E-slash to be consistent with the rest of the paper.

Axis label changed; these plots are recreated to be more in line with PubComm recommendations.

Figure 5: the plot header e/mu + >bjj+gg suggests that this is CS * acceptance going into SR2 only. Is it? If so, shouldn't there be a second plot for SR1?

Now this reads e\mu + >= bjj+gamma(gamma). Information dense, but more correct. It is all four channels so some events here are "gamma" and some "gamma gamma".

Figure 5 :Is it possible to show cross section limits for the diagonal region above mStop-mBino < mt? It would be good to show this for the sake of understanding how close to the diagonal can be excluded. Someday someone may want to do a study to exclude part of the diagonal and that information will be useful.

This was discussed before pre-approval quite a bit, and what we concluded was that this area needs a much finer mass binning than was available. Furthermore it wasn't clear that the MC was handling off-shell top decays or the possibility of charms (stop -->

charm + bino) correctly, whereas in the rest of the mass grid these aren't concerns. This analysis has very low acceptance in this region due to requiring high-PT leptons and b-jets, so we decided it was best just to not report results in this region.
In the future I agree it would be interesting, although triggering on leptons and requiring b-jets isn't ideal. The inclusive di-photon MET search could perform well here, and when the chance arises I like to remind that group of this. A specialized search would be needed to have significant sensitivity here.

Figure 2: significant figure clean up needed: Larger fonts everywhere. The horizontal axis label interferes with the number markings (hist->GetYaxis()->SetTitleOffset(0.5) ). Make the figures either all log or all linear. For the log plots, make a more sensible choice of vertical scale, going no lower than 10^2. In the horizontal axis title. make the c^2 into a superscript or drop it completely. Remove the legend titles or make them make sense instead of having both the left and right figures labeled "ele" when one is ee and the other is e-gamma.

Plots are remade for PubComm suggestions. Also axis range and labels. Third plot is also log-scale to match.

Figure 3: use larger fonts for everything except the CR2 labels. In the legend, equalize the length of the two columns of entries. This will create vertical space in the legend which should then be used to make the font larger. Use a larger marker (In Anthony's CMSStyle file: PrettyMarker(hist, kBlack, 3 or 4); ) CR2 ele looks to not be using Poisson error bars. Always use Poisson error bars for the data: hist->SetBinErrorOption(TH1::kPoisson).

Plots are remade for PubComm suggestions, and are somewhat different now. Not quite sure how you mean the error bars appear, but in CR2 the y-axis is log-scale and is quite low in value, giving the error bars the appearance of being asymmetric -- they are displayed the same as in all other plots.

Table 2: fill down the Notes rather than using tick marks.

Okay.

  • Physics comments*
  • Section 1:

4-5 The statement that SUSY keeps particles with large couplings to the higgs boson light seems to be a self-contradictory statement, as well as not indicating the third generation squarks.
rewrite -- commas separating "particles (of) light" --> "particles (of things coupling high) are light"

Agree, interesting semantic ambiguity here. Fixed a bit, now reads:
"... models of SUSY in which, for Standard Model particles with large couplings to the Higgs boson, their sparticle partners are kept light, namely the third-generation..."

  • Section 2:
line 66 or 97: please specify the shower shape requirement. I think you mean a sinin cut, in which case, please specify the cut value.

You are correct, but it is not common practice to include the term "\sigma_{i\eta i\eta}" or to define precise cut values. The phrase used is standard in CMS publications.

  • Section 3:
line 72: Please specify which type of isolation is being applied to the muons?

As this is all isolation types, the current wording seems to be the most efficient as it parallels the wording for photons (line 67) and electrons (line 76).

  • Section 4:
line 103: please specify the cut parameters of the fake photon definition.

As from a previous comment, CMS papers don't generally define sigmaIetaIeta and leave it as a "photon-like shower shape". Therefore simply saying these must fail the cut seems most appropriate.

line 118: which version of MadGraph?

Included version 5.1.3

Table 1: Why do the electron and muon channels have different k-factors (SF_Z)? If it's the cross section that the monte carlo gets wrong, we should expect a single k-factor.

Some of these factors were incorrectly named as k-factors. They are now appropriately named just 'scale factors', and so the difference between electron and muon channels less confusing.

line 136-137. I'm confused whether this fit is going on in data or in monte carlo. Presumably this template fit is being made in data. So why is a k-factor being applied?

This section has been extensively rewritten for clarity. The fit is done of data to MC backgrounds, and a scale factor is derived for the MC so as to better describe the data. The k-factor language has been removed.

lines 136 to 149: The description of the electron to photon fake rate scale factor is very unclear and confusing. Here's my confusion: Is the fit described on line 136 done on data or monte carlo? If it is done on data, why are you applying a k-factor to it. If it is being done on monte carlo, then are you applying this MC truth matching on top of the template? That would also make no sense since you could simply eliminate the fit entirely and just do MC truth matching to determine the fake rate. The use of a k-factor on the template fit indicates that this fit cannot possibly be done on data, and yet in order to make a scale factor there has to a measurement somewhere, what is it? Then, the b-tag requirement is removed but the fit is done in SR1, so it's not SR1, but instead some new loosened version of SR1. Finally, how is this second scale factor applied?

Again, now called more correctly a 'scale factor' which is an expression of both MC and data. The fit is done as a fit of two MC background templates to the data, and the truth-matching is done to the templates to better separate them. Truth-matching alone on MC, without a fit to data, only gives a measurement of the fake rate in MC and not a scale factor adjustment to data. As for 'not SR1', the current language should be more expedient than introducing an entirely new control region definition. As said, this section has been largely rewritten.

Line 167: it appears that CR2 is never used, so why not strike it from the PAS and just mention that it was considered and has too little statistics to be of any use.

This is a fair point to be discussed more; it did not come up during pre-approval. The argument to keep it is that it does show the reader that there is a fair agreement between data and MC in CR2, even though the sample is too limited to extract just how quantitative that "fair agreement" is.

Lines 168-172: How is this additional shape systematic determined? Table 3 shows significant excesses in three out of four channels. This strongly suggests that the background is inadequately modeled. SR1-ele constitutes a 3 sigma excess; SR1-muon a 2 sigma excess, and SR2-muon a 2.3 sigma excess.

Expanded on the additional shape systematic: it is calculated by the ratio of shapes of MET in signal and control regions. In more detail, if you suppose the agreement of data and MC is perfect in a CR, you have the verification that the MC was able to simulate the shape of MET in that CR perfectly. If however the shape of MET in a CR is different in one bin from the signal region shape by 5%, then you only have a verification that the MET was able to simulate something 5% different from a signal region correctly. So in this simple example, you would add an extra 5% uncertainty to that one bin due to this. In reality it is not just one bin, and the scale on this uncertainty is fairly small.
For Table 3 and the excess comment, again this table clearly did not show the correct uncertainties -- there is a sqrt(N) everywhere that is not explicitly shown. New tables showing the correct uncertainties have been made.

line 143,153: why doe the need for a tt+gg sample depend on the photon purity? You say the cross section is "exceedingly small" so either the cross section makes it negligible or it needs to be accounted for somehow. This might make sense if you are bumping up the tt+gamma or tt+jet cross section to account for the tt+gg and then saying that it doesn't matter where the apparent photons come from. But that should have different contributions to SR1 and SR2. Why is met shape important rather than the relative contributions to SR1 and SR2?

There are tt+gg events simulated in the samples used; what is not used is an explicit, specialized tt+gg sample where both photons are high-PT and with large radiation angles. The cross section for such events is very very small. You often have high-PT photons (a single one) which is why the specialized sample of tt+gamma is needed, but you do not expect both photons to be in the tails of quickly falling PT distributions. What most of the selected SR2 events contain are mis-identified jets (as photons) or prompt photons where only one or zero of them are considerably high in PT or radiation angle. Remember that in all samples there are additional jets simulated, so "tt+gamma" is in reality "tt+gamma+jets" where some of those "+jets" do include photons ("+a") in MadGraph parlance.
The real question then is: do the "+jets" from MadGraph have the right number of photons, the right amount of electromagnetic fluctuation in jet hadronization? The resolution the analysis came to and that was discussed in pre-approval was that without a precise measurement of the SM tt+gg cross section, you could not be sure -- however if the MET distribution is the same between "+jets" contributions, then you could do a shape-based analysis independant of the absolute rate. What the analysis should accomplish is an estimate of the MET from the selected photons, and not try to pin down how much is due to actual photons.
This is the crux of the shape-based analysis and why the background normalizations are allowed to float. If it were possible to measure the SM tt+gg cross section with the 2012 dataset (ie real ttbar + prompt + prompt with a complete di-photon purity measurement), it would be possible to do this analysis with absolute background normalizations.

Line 155-156: These lines are completely unclear; I have no idea what this is attempting to communicate. Here's my confusion: The upper limit determination of what? Shape based interpretation of what the shape of what? What result?

Now: "backgrounds are allowed to float freely in the upper limit calculations so that the interpretation of the results is completely shape-based. This is accomplished by givin the total background in each channel and signal region a 100\% systematic uncertainty, flat in \MET." I don't think it necessary to explain to the reader again how the results of the analysis are interpreted.

  • Conclusion:

line 200-201: "No significant excesses are observed..." you have no right to make such a claim while showing strong excesses in Table 3.

Table 3 does not show a significant excess when the counting statistics and systematics are included. What is more on this point, Table 3 as-is clearly does not match Figure 4. What is different between Table 3 and Figure 4 is that it's customary to include sqrt(N) uncertainties on the observed data points, but it's not typical to quote observed data as N +/- sqrt(N) in tables. That was the source of the mistake in creating Table 3, and the re-made versions of the table now include counting statistics on the background estimates.

Figure 6: How is it possible that the observed limit exceeds the expected limit while Table 3 shows 2 and 3 sigma excesses in 3 of the 4 channels?

See above comments about uncertainties in Table 3. Furthermore the wording of the conclusion has been adjusted to include shape, saying "No significant excess in the shape of the MET distribution is observed that would indicate the presence of new physics."

Figure 6: It would be good to see how the expected limit curves fall at the diagonal.

As from another comment, I would agree. However special care must be taken for this region, and a very fine mass binning of models (ie many samples) is needed that was not available. Furthermore, requiring high-PT leptons and b-jets severely limits acceptance in this region. A completely different analysis, or even the inclusive di-photon MET search, would be much better suited for this region.

 
 
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