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2015:groups:tools:backgrounds [2015/06/03 15:41] jonathan.butterworth [WW versus ttbar] |
2015:groups:tools:backgrounds [2015/06/03 17:54] jonathan.butterworth |
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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). | ||
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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 ==== | ||
Link to the ATLAS paper: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2012-11/ | Link to the ATLAS paper: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2012-11/ | ||
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Here's the plot of the unsubtracted measurement, with the predicted single-top contribution shown: | Here's the plot of the unsubtracted measurement, with the predicted single-top contribution shown: | ||
+ | {{ :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. | ||