Jon Butterworth, Paolo Francavilla, Frank Krauss, Carlo Pandini, Luca Parrozzi, …

github repository: https://github.com/perrozzi/leshouches_bkgsub (see below for details)

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:

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) The ATLAS paper is here: https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2012-01/

3. Consider WWbb as the signal, motivated by WWH (H→bb). Same study (DR/SR/C/Sum).

Semi-leptonic channel:

4. Consider ttbar as signal. Look at distortion in b-lepton mass from SR/C/Sum/WWbb-non-top contributions.

Link to the ATLAS paper: http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2012-11/

This would be a nice demo of some of the ideas above with a real measurement. Treat Wb excluding t as the signal, use the ATLAS Wb (unsubstracted) measurement and re-evaluate the single-top subtraction and systematics.

The paper reports an measurement (2011 data) of Wb, in two versions. In the one case, single top is considered as part of the signal; in the second it is subtracted.

Here's the plot of the unsubtracted measurement, with the predicted single-top contribution shown:

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.

To setup your local repository

1. go to github.com and get an account
2. log in, go to https://github.com/perrozzi/leshouches_bkgsub
3. In the top-right corner of the page, click Fork
4. open a shell where git is available
5. clone the repository with the command: git clone git@github.com:your_git_username/leshouches_bkgsub.git
6. enjoy

To start contributing

1. modify/add a file
2. add file(s) to local repository: git add filename.bla
3. commit file(s) to local repository: git commit -m “commit messate” filename.bla
4. “push” modifications to your remote (i.e. github) repository : git push
5. inform Luca to include your modifications to the main repositiry

To synch your repository with the main repository

1. git pull https://github.com/perrozzi/leshouches_bkgsub.git master