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Comments on text ATLAS Preliminary  ATLAS Internal

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Comments on text ATLAS Preliminary  ATLAS Internal

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  1.  I'm concerned that the OS requirement for the signal is inefficient as the charge of the TeV scale leptons can be easily mis-assigned. As a result we do not only loose some signal but also contaminate the SS control region that is used to estimate the QCD in the OS signal region. So we either should take into account the contamination of the signal in the SS control region in the limit setting procedure (and loose sensitivity) or we change the strategy of estimating the QCD to a matrix method using non-isolated lepton selections. Can you show the charge assignment for the signal? • Answer: Studies on 8 TeV ATLAS data have found no evidence for combined muon charge misID[ATLAS Collaboration Collaboration, J. A. et al., Search for heavy neutrion, WR and ZR gauge bosons in events with two high-PT leptons and jets with the ATLAS detector in pp collisions at sqrt(s) = 8 TeV] since the muon charge flip rate is immeasurably small it is neglected in this analysis.For taus, the average of the track is much lower that for electrons or muons due to the neutrino and other hadrons in the tau decay.  For electrons, an exotic study(ATL-COM-PHYS-2013-990), shows that the charge mis-ID at TeV level is ~3%. This is similar as our 7TeV study which concluded negligible effect considering the QCD fraction is small(<10% level). So in our study, the charge ID effect on bkgd estimation is very small, we can mention this point in our new update. • Concerning the signal efficiency lost, in fact, for a 500GeV(1TeV, 2TeV, 3TeV) emu signal sample, if we simply remove the charge OS requirement, the efficiency gain is only 2%(3%, 5%, 7%), the number for etau at 3TeV is 12%. But we know, the Wjet and QCD background will be almost doubled in such a case, so a OS requirement is still necessary

  2. The W+jets estimation may not be reliable from MC (even after normalization) as the fake rate of taus is known to be mis-modeled in the MC. See for example Figures: 18b, 19b, 21b, 23b, What is the reason not to use the SS control region (or the matrix method) also for the W+jets and other processes where one of the leptons is fake? At the same time, when estimating the contributions from physics processes we should make sure using truth information that we are selecting real leptons and not fakes to avoid double counting • Answer: yes, Wjet estimation from MC is not reliable. For Wjet background number estimation, we use a semi-data driven method as you see in section 6, for the Shape, we use MC. So, we also perform many validations for Wjet(small dphi region, Wjet enhanced small dphi region, SS Vs OS, in section 6) background which shows our method is reasonable. Finally, we assign a 20% uncertainty on Wjet Shape. Besides, yes, we’re sure there’s no double counting. • The reason why we don’t use SS control region for Wjet is that: In Wjetestimation, we use a lepton pt cut(pT<150GeV) to keep the control region orthogonal to our signal, so we wouldn't have any high pt lepton events, which are the most important part of our search. 

  3. If I understand correctly, at the moment the W+jets normalization region is not orthogonal to the SR. Can you make them orthogonal? • Answer: In fact, we have a lepton pT cut to make sure there’s no signal leakage, you can find it in section 6.2. So they should be orthogonal • l292: do you require that all leptons are separated from jets by 0.4 in dR? Usually people do that. • Answer: in fact, Lorenzo suggested us to require that all leptons except muons should be separated from jets by 0.4 , since muon is hardly to fake as a jet, so we applied that.

  4. -Section 4: given the small mass of the tau, not only the eta of the MET should be the same as as for the tau, but also the phi. So one should use only the parallel component (wrt to the tau) of the MET to correct the mass and use the perpendicular component to apply an upper cut to suppress the WW and tt backgrounds. • Answer: For the signal, delta phi between the missing Et and the tau is always small, so it doesn't make any difference.  For the background, it is just a procedure and it doesn't matter what we do.  We checked for the 7 TeV analysis that the method we use does not bias the background. • Figure 22 and 23b, why does the QCD has 2 events in last bins? • Answer: for QCD shape, we got it as follows: so we think this can happen considering the large statistical fluctuations at high mass region, but as you see, when we do signal search we simply integrate all the bins above 1 TeV to cope with the statistic problem

  5.  To set limits, I was expecting to have predefined bins in the invariant mass, that are as large as the resolution of the detectors for that mass and have an estimate of background for all of them. Then use all bins in a simultaneous fit when setting the limit on a particular signal. At the moment the choice of bins is driven by the signal points considered and they are too large compared to the resolution. • Answer: For our signal sample, the step of Mass point is 50GeV(100GeV for high mass samples,   500GeV for Z' when >2TeV).  In table 14 we just picked out several signal samples for an example which makes the table a bit shorter.  Our Mass window is  M+- 3*sigma, so the smallest mass window is at 100GeV level. Our signal samples is detailed in Section 2, probably we can explain table 14 a bit. 

  6. I was expecting the PDF uncertainties to be important for the physics backgrounds but I do not see them mentioned. • Answer: It is included in the MC cross-section part, see l484

  7. Comments on text • ATLAS Preliminary  ATLAS Internal • Many plots would benefit from rebinding to avoid the large statistical fluctuations(Fig 13-24) • It would be nice to introduce a name for all regions that are used in the analysis, and write this name in each plots. Also make a table with the definition of all the regions •  Conclusions need to be updated to the 2012 analysis Other comments 1. More details on systematics: how the systematics are calculated for both low mass region/high mass region and limit setting • More Details on the background fit: parameters, error, chi^2 • The composition of the background in the mass windows with the suggestion of providing the sharing in three different ranges including the high mass tails M > 1 TeV.

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