1 Measurements at 8 TeV of TTbar events with additional particles in the final state Boris Mangano...
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![Page 1: 1 Measurements at 8 TeV of TTbar events with additional particles in the final state Boris Mangano (ETH Zürich) on behalf of the CMS collaboration Boris.](https://reader036.fdocuments.us/reader036/viewer/2022062714/56649d0e5503460f949e30e6/html5/thumbnails/1.jpg)
page 1
Measurements at 8 TeV of TTbar events
with additional particles in the final state
Boris Mangano (ETH Zürich)
on behalf of the CMS collaboration
![Page 2: 1 Measurements at 8 TeV of TTbar events with additional particles in the final state Boris Mangano (ETH Zürich) on behalf of the CMS collaboration Boris.](https://reader036.fdocuments.us/reader036/viewer/2022062714/56649d0e5503460f949e30e6/html5/thumbnails/2.jpg)
LHCP 2014Boris Mangano page 2
Outline
TTbar plus what?
- TTbar+jets
- TTbar+BBbar
- TTbar+V:
o TTbar+gamma
o TTbar+Wo TTbar+Z
8TeV results released during the last 12 months
Were these processes seen also at 8TeV ?
new results
PAS TOP-12-041
PAS TOP-13-010
PAS TOP-13-011
8 TeV
TOP-12-018
PAS TOP-12-024
TOP-12-014
7 TeV
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LHCP 2014Boris Mangano page 3
Motivation
TTbar plus what?
- TTbar+jets
- TTbar+BBbar
- TTbar+V:
o TTbar+gamma
o TTbar+Wo TTbar+Z
About ½ of TTbar events contain extra jets with |h| < 2.4, pT>30 GeV. Possibility to test higher order QCD calculations.
Irreducible non-resonant background for ttH (H->bb) analysis.
Potential to verify if couplings to the top quark are compatible with SM or altered by BSM effects.
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LHCP 2014Boris Mangano page 4
tt+jets @ 8TeV (19.6 /fb)PAS TOP-12-041Event selection:
- Dilepton OS events (el and mu)- For same-flavour pairs, Z-veto
and require MET- N-jets >=2- N-bjets >=1
Unfolding:- cross-section in N-jets bins is
presented at particle level
Extra jets definition:- Kinematic reconstruction
method to identify b-jets from ttbar decay.
- Other extra jets are then analysed
Main source of uncertainty:Up to 20% uncertainty from jet-energy-scale and signal model uncertainties.
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LHCP 2014Boris Mangano page 5
The whole is greater than the sum of its parts (Aristotle)
MC@NLO + Herwig does not generate sufficiently large jet multiplicities.
tt+jets @ 8TeV (19.6 /fb)
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LHCP 2014Boris Mangano page 6
The whole is greater than the sum of its parts (Aristotle)
Leading extra jet pT (GeV)
tt+jets @ 8TeV (19.6 /fb)
Second Leading extra jet pT (GeV)
These distributions are at reconstruction level
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LHCP 2014Boris Mangano page 7
PAS TOP-13-010Event selection:- Dilepton OS events (el and mu)- For same-flavour pairs, Z-veto and
require MET- N-jets >=4- N-bjets (tight) >=2
tt+bb@ 8TeV (19.6 /fb)
Main source of uncertainty:20-25% total uncertainty. Mostly from uncertainties in b-tagging discriminator templates.
Normalization of simulated samples:- Performed by means of a fit to the
measured b-tagging algorithm discriminator.
- Templates for different tt+X samples (including tt+bb signal) are taken from simulation.
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LHCP 2014Boris Mangano page 8
The whole is greater than the sum of its parts (Aristotle)
First additional jet Second additional jet
Simultaneous template fit of two data distributions
tt+bb@ 8TeV (19.6 /fb)
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LHCP 2014Boris Mangano page 9
The whole is greater than the sum of its parts (Aristotle)
Factor 0.38 to account for difference in selection efficiency between ttbb and ttjj (from simulation)
Cross-section ratio at particle level:
tt+bb@ 8TeV (19.6 /fb)
using again selection efficiencies from simulation
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LHCP 2014Boris Mangano page 10
PAS TOP-13-011Event selection:
- one isolated central m with pT > 26 GeV - Veto on extra leptons- N-jets >=4, with pT > 55, 45, 35, 20 GeV- N-bjets >=1- One central photon ET > 25 GeV- DR (photon,muon) > 0.7
tt+gamma @ 8TeV (19.7 /fb)
Main source of uncertainty:20-25% total uncertainty from modelling of the background template.
Signal extraction:
- Template fit of charged-hadron-isolation discriminant distribution in data.
- Templates for signal and misidentified photons from simulations.
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LHCP 2014Boris Mangano page 11
tt+gamma @ 8TeV (19.7 /fb)
N-1 plots for some of the observables used to select the signal photons.
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LHCP 2014Boris Mangano page 12
The whole is greater than the sum of its parts (Aristotle)
tt+gamma @ 8TeV (19.7 /fb)
Fit of distribution of thecharged-hadron-isolation discriminant
Inclusive ttbar cross section (TOP-12-017)
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LHCP 2014Boris Mangano page 13
ttW and ttZ @8TeV (19.5 /fb)
- Both ttW and ttZ processes are very rare and the measurement of their cross sections can be used to test the internal consistency of SM.
TOP-12-036
pre-print to be released in the next days
- ttZ production allows the probe of tZ coupling.
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LHCP 2014Boris Mangano page 14
ttW in same-sign dilepton
Signal region definition:- Tight prompt-lepton selection- same-sign dilepton (el or mu)- third lepton vetoed only if it makes a
Z-candidate- N-jets >= 3- N-bjets >=1- lepton pT>40 GeV and HT > 155 GeV
Analysis type:counting experiment
Against misidentified prompt leptons and ttbar background
Against WZ and other diboson processes. Remove overlap with ttZ analysis.
Final optimization against ttbar background
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LHCP 2014Boris Mangano page 15
ttW in same-sign dileptonDominant background:
- ttbar with misidentified leptons is estimated from data. Uncertainty is about 50%.
Other backgrounds:
- ttZ, WZ and other rarer processes are estimated from simulations.
- Z+jets with mis-measured lepton charge estimated from data
Six signal regions to exploit larger S/B in plus-plus channels.
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LHCP 2014Boris Mangano page 16
ttZ in trilepton
Analysis type:counting experiment
Signal region definition:- Three tight leptons (el or mu)- Two same-flavour opposite-sign
making a Z-candidate- N-jets >= 4- N-bjets (loose) >=2 & N-bjet
(medium) >=1
Against misidentified leptons and ttbar background
Against WZ and other diboson processes. Remove overlap with ttW analysis.
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LHCP 2014Boris Mangano page 17
ttZ in trileptonDominant background:
- non-top-quark background processes with b-jets from ISR. Uncertainty is about 50%.
Other backgrounds:
- TTbar with misidentified leptons is estimated from data.
- Rarer, and irreducible, SM processes estimated from simulation
Only one signal region is used for the statistical interpretation of the data
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LHCP 2014Boris Mangano page 18
ttZ in four-lepton
Analysis type:counting experiment
Signal regions definition:- Four tight leptons (el or mu)- Two same-flavour opposite-sign
making a Z-candidate- Veto on second Z-candidate- N-bjets =1- N-bjets >1
Against WZ and lepton misidentification
Two non-overlapping signal regions
Against ZZ background
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LHCP 2014Boris Mangano page 19
ttZ in four-leptonBackgrounds:
- ZZ(*) in four leptons is estimated from MC
- Z+X events with misidentified leptons
Limits and benefits of this channel:
- statistically limited
- Large S/B ratio
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LHCP 2014Boris Mangano page 20
ttV (V = W or Z)
Results in agreement with SM predictions:
cross section ttW = 206 ± 23 fbcross section ttZ = 197 ± 25 fb
Numbers from MG5_aMC@NLO. They are compatible with first NLO calculations from MCFM and PowHel.
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LHCP 2014Boris Mangano page 21
Summary
TTbar plus what?
- TTbar+jets
- TTbar+BBbar
- TTbar+V:
o TTbar+gamma
o TTbar+Wo TTbar+Z
8TeV results released during the last 12 months
PAS TOP-12-041
PAS TOP-13-010
PAS TOP-13-011
TOP-12-036
pre-print to be released in the next days
New Results
![Page 22: 1 Measurements at 8 TeV of TTbar events with additional particles in the final state Boris Mangano (ETH Zürich) on behalf of the CMS collaboration Boris.](https://reader036.fdocuments.us/reader036/viewer/2022062714/56649d0e5503460f949e30e6/html5/thumbnails/22.jpg)
Latsis Symposium 2013 page 22Boris Mangano
Backup slides
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LHCP 2014Boris Mangano page 23
ttV (V = W or Z)
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LHCP 2014Boris Mangano page 24
The whole is greater than the sum of its parts (Aristotle)
tt+jets