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2015:groups:tools:backgrounds [2015/06/03 15:41]
jonathan.butterworth [WW versus ttbar]
2015:groups:tools:backgrounds [2015/07/14 08:31] (current)
philippe.gras Added instructions for CERN account
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 ====== A quick study on the impact of irreducible-background subtraction ====== ====== A quick study on the impact of irreducible-background subtraction ======
  
 +//If you are interested in contributing please subscribe to the [[https://​e-groups.cern.ch/​e-groups/​EgroupsSearch.do?​searchValue=houches-2015-topics-tools-bgnd-subtraction|mailing list]]. You will be asked to log in with your CERN account. If you don't have a CERN account, please fill [[https://​account.cern.ch/​account/​Externals/​RegisterAccount.aspx|this form]] to create a lightweight account.//
  
- +Jon Butterworth, Vitaliano Ciulli, Paolo Francavilla,​ Frank Krauss, Carlo Pandini, Luca Parrozzi, ...
-Jon Butterworth,​ Paolo Francavilla,​ Frank Krauss, Carlo Pandini, Luca Parrozzi, ...+
  
 github repository: https://​github.com/​perrozzi/​leshouches_bkgsub github repository: https://​github.com/​perrozzi/​leshouches_bkgsub
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 14 TeV (maybe also 13 TeV), B-tag up to y=2.5 (allowing a veto on b-jets in this region if it helps). Also look at the impact of pseudo-top vetos. ​ 14 TeV (maybe also 13 TeV), B-tag up to y=2.5 (allowing a veto on b-jets in this region if it helps). Also look at the impact of pseudo-top vetos. ​
  
-Double leptonic channel:+Double leptonic channel ​(eμ only):
  
 1. Consider WWjj as the signal. Look at WW scattering-like WWjj topologies. Study the contribution to the signal coming from double-resonant (DR), single-resonant (SR) and continuum (C) ttbar processes, and the sum. 1. Consider WWjj as the signal. Look at WW scattering-like WWjj topologies. Study the contribution to the signal coming from double-resonant (DR), single-resonant (SR) and continuum (C) ttbar processes, and the sum.
  
 2. Consider WWj or WW as the signal. Look at jet-binning for for all WW (not just the VBS topology). Same study (DR/​SR/​C/​Sum) 2. Consider WWj or WW as the signal. Look at jet-binning for for all WW (not just the VBS topology). Same study (DR/​SR/​C/​Sum)
 +The ATLAS paper is here: https://​atlas.web.cern.ch/​Atlas/​GROUPS/​PHYSICS/​PAPERS/​STDM-2012-01/​
 +The cuts which define the fiducial phase space are:
 +  * pT μ > 20 GeV (muon or electron), leading lepton pT > 25 GeV
 +  * muon |η| < 2.4, electron |η| < 1.37 or 1.52 < |η| < 2.47, 
 +  * no jets with p > 25 GeV, rapidity |y| < 4.5 and separated from an electron by ∆R > 0.3
 +  * pT (ll') > 30 GeV
 +  * m(ll′) > 10 GeV, pT,Rel > 25 GeV
 +
 +I (Jon) suggest we simplify this to something like:
 +  * pT leptons all > 25 GeV
 +  * |η| leptons all < 2.4
 +  * m(ll′) > 10 GeV
 +  * count the jets, and b-jets, with p > 25 GeV, rapidity |y| < 4.5 
 +
 +... but I haven'​t check the CMS paper yet.
 +
  
 3. Consider WWbb as the signal, motivated by WWH (H->bb). Same study (DR/​SR/​C/​Sum). 3. Consider WWbb as the signal, motivated by WWH (H->bb). Same study (DR/​SR/​C/​Sum).
 +For HH->​WWbb,​ a possible proposal could be:
 +
 +Objects Definition: ​
 +  * electrons and muons: pT > 25 GeV; |eta| < 2.4
 +  * jets: pT > 25 GeV; | eta | <4.5
 +  * bjets: jets with | eta |< 2.5 and b-labelled
 +
 +NOTE 1: in the ATLAS WW analysis, the jets are build from all the particles, excluding muons and neutrinos.
 +If we adopt this definition, we will need to run an Overlap Removal between electrons and jets, to avoid counting jets which are in fact electrons. ​
 +NOTE 2: The ATLAS WW analysis is vetoing events if (among the other selections) :
 +  * there are jet (and b-jet), or
 +  * there are extra leptons.
 +If we want to extend to events with b-jets, we should consider how to handle the semi-leptonic b-decays in jets ()to avoid to veto the event because of the leptons in jets. 
 +
 +Event Selection:
 +fill()CutFlow
 +  * 2 opposite charged leptons
 +  * 1 muon, 1 electron
 +fill(CutFlow)
 +fill(MET_rel)
 +  * MET_rel>​25 GeV,
 +fill(CutFlow) ​
 +fill(mll)
 +  * mll>10 GeV, 
 +fill(CutFlow)
 +fill(b-jets,​ jets) #b-jets VS #jets
 +fill(jets), pt, eta
 +  * 2+ bjets
 +fill(CutFlow)
 +fill(bjet 1) pt, eta
 +fill(bjet 2) pt, eta
 +fill(electron) pt, eta
 +fill(muon) pt, eta
 +fill(MET) ​
 +fill(mT(MET,​e,​mu)) ​
 +  * 100<​mT(MET,​e,​mu)/​GeV<​150
 +fill(CutFlow)
 +fill(electron) pt, eta
 +fill(muon) pt, eta
 +fill(b-jet1) pt, eta
 +fill(b-jet2) pt, eta
 +fill(m(bb))
 +  * 100<​m(bb)/​GeV<​150
 +fill(CutFlow)
 +fill(b-jets,​ jets) #b-jets VS #jets
 +fill(jets), pt, eta
 +
 +
 +NOTE: it would be nice to use some top veto.
 +the pseudo-top definition could be a nice idea, but it is defined ​
 +in a straightforward way for the Semi-leptonic channel.
 +One can test the b-lepton mass (associating the b to the closer lepton).
 +
  
 Semi-leptonic channel: Semi-leptonic channel:
  
 4. Consider ttbar as signal. Look at distortion in b-lepton mass from SR/​C/​Sum/​WWbb-non-top contributions. 4. Consider ttbar as signal. Look at distortion in b-lepton mass from SR/​C/​Sum/​WWbb-non-top contributions.
- 
 ==== Wb versus t ==== ==== Wb versus t ====
  
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 {{ :​2015:​groups:​tools:​wb.png?​400 |}} {{ :​2015:​groups:​tools:​wb.png?​400 |}}
  
 +Integrated over pT, the measurements are:
 +
 +Unsubstracted:​
 +
 +  * σfid (1 jet) = 5.9 ± 0.2 (stat) ± 1.3 (syst) pb,  (fractional syst = 22%) 
 +  * σfid (2 jet) = 3.7 ± 0.1 (stat) ± 0.8 (syst) pb,  (fractional syst = 22%)
 +  * σfid (1+2 jet) = 9.6 ± 0.2 (stat) ± 1.7 (syst) pb.(fractional syst = 18%)
 +
 +Subtracted:
 +  * σfid (1 jet) = 5.0 ± 0.5 (stat) ± 1.2 (syst) pb,  (fractional syst = 24%)
 +  * σfid (2 jet) = 2.2 ± 0.2 (stat) ± 0.5 (syst) pb,  (fractional syst = 23%)
 +  * σfid (1+2 jet) = 7.1 ± 0.5 (stat) ± 1.4 (syst) pb.(fractional syst = 20%)
  
 +So there is a small but noticeable effect. The main contributions to the systematic errors quoted in the paper are:
 +  * Jet energy scale 10-50%
 +  * ISR/FSR, including on single top and ttbar 2-30%
 +  * b-tagging 1-8%
 +  * MC modelling (but only of the Wb "​signal"​) 2-8%
 +So I guess the fact that JES dominates is why the effect is fairly small. The "​ISR/​FSR"​ thing, which should be reduced for the unsubtracted measurement,​ varies a lot with jet pT. Indeed, if you compare Table 4 with Table 9 in the paper, you can see this. In the highest pT bin the systematic uncertainty goes from 16% before subtraction to to 54% after it.
  
  
2015/groups/tools/backgrounds.1433338911.txt.gz · Last modified: 2015/06/03 15:41 by jonathan.butterworth