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--- 2015:groups:tools:backgrounds [2015/06/03 15:40]
jonathan.butterworth [Wb versus t]
+++ 2015:groups:tools:backgrounds [2015/07/14 08:31] (current)
philippe.gras Added instructions for CERN account
@@ Line 1: / Line 1: @@
 ====== 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
@@ Line 14: / Line 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):
 . 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.
 . 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.
 . Consider WWbb as the signal, motivated by WWH (H->bb). Same study (DR/SR/C/Sum).
+For HH->WWbb, a possible proposal could be:
-Semi-leptonic channel:
+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
-. Consider ttbar as signal. Look at distortion in b-lepton mass from SR/C/Sum/WWbb-non-top contributions.
+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:
+. Consider ttbar as signal. Look at distortion in b-lepton mass from SR/C/Sum/WWbb-non-top contributions.
 ==== Wb versus t ====
@@ Line 39: / Line 104: @@
 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.

Les Houches

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