1. ELECTROWEAK AND TOP RESULTS AT LHC
Jose Enrique Garcia – IFIC-Valencia

2. Electroweak and Top cross-sections
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3. ELECTROWEAK

4. Electroweak 1
Electromagnetic and Weak probes in hadron-hadron collisions
Clean signature with lepton/photon/ETmiss 2
Benchmark of SM validation at high energy
Large mass of W/Z assures hard scale involved 3
Measurements at extreme kinematic topologies allow tuning of MC tools
(N)NLO calculations, MC event generators 4
Crucial in searches for Beyond-SM physics
Signal typically involves W/Z/…
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5. INCLUSIVE W/Z Special data with low pile-up arXiv:1402.0923
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6. W+JETS
Important background for many processes, it needs to be properly modeled. Comparison with different generators :
NLO BLACKHAT+Sherpa does a good job for most of the distributions
Discrepancy observed for ET sum of all jets (ST in ATLAS, HT in CMS)
ATLAS-CONF
arXiv:
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7. W+JETS Discrepancy also seen in : dijet mass, Δφ(jet1,μ)
Data are crucial input for tuning MC generators
ATLAS-CONF
arXiv:
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8. W+bb Largest background for top-quark pair production
Well separated 2 b-jets ⟶ less theoretical uncertainty
arXiv:
PLB735 (2014) 204
Theory :
Conclusion?
similarly ATLAS W+b : JHEP06 (2013) 084
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9. WW Parallel session talk
ATLAS-CONF
LHC measurements showed an enhancement of data compared to theory in the di-boson x-section.
Latest measurement made it more evident :
Parallel session talk
Check conf
Possible issues :
→ Experimental systematics? → Higher-order corrections beyond NLO QCD?
→ Theoretical uncertainty for calculation of jet veto (NNLL resummation)?
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10. WW SCATTERING final states : W±W± jj→l±ν l±ν jj (l=e, μ)
ATLAS : arXiv:
final states : W±W± jj→l±ν l±ν jj (l=e, μ)
Very rare SM process and can be used as test for BSM, first evidence the VVVV vertex
Challenging analysis due to dominant WW production (QCD)
EWK-VBS
First evidence for vector boson scattering
Check CMS note
ATLAS : 3.6σ/2.8σ(observed/expected)
CMS: 2.0σ/3.1σ (observed/expected)
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11. TOP

12. Theoretical Predictions
TOP PRODUCTION AT LHC
At the peak of instantaneous luminosity during 2012 the top production was :
Around 15M quark tops were produced during 2011 and 2012!
~ 2 top pairs/s
~ 1 single top/s
LHC
Theoretical Predictions
table with values??
references!!!
s-channel1
t-channel2
Wt-channel3
top pairs4
7 TeV
8 TeV
1 Phys. Rev. D 81, (2010) Phys. Rev. D 83, (R) (2011) 3 Phys. Rev. D 82, (2010) 4 NNLO+NNLL (Top++2.0)
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13. WHAT MAKES TOP QUARK INTERESTING?1
Heaviest fundamental particle in the Standard Model
Larger mass ➙ Larger coupling to SM Higgs + mtop is a fundamental parameter in SM
Allows for Self-Consistency Checks of SM Post Higgs Discovery 2
Short Lifetime(~10-25 s)
Decays before hadronization – Unique among the quarks!
Access to Polarization and Spin Correlations 3
Processes including top are backgrounds for new physics
+ Exotics and SUSY
Good Understanding ➙ Improvements in Searches 4
Hints of new BSM/physics?
Exotic Particles Could Decay Preferentially to Top Quarks
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14. WHAT CAN WE MEASURE? POLARIZATION CROSS-SECTION PDF SPIN, COUPLINGS
MASS,…
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15. TOP QUARK PRODUCTION Decay Modes
single top : production via EW interaction
top pair production
Decay Modes
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16. TOP QUARK PRODUCTION Most Common Experimental signatures Backgrounds
top pairs : depending on the decay channel
t-channel : 1 isolated leptons (e / μ), one b-tagged jet, 1 forward jet, missing ET
Wt channel : 2 isolated leptons (e / μ), one b-tagged jet, missing ET
s-channel : 1 isolated lepton (e / μ), two b-tagged jets, missing ET
Backgrounds
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17. INCLUSIVE TT CROSS-SECTION
All channels measured ➞ no new physics
Parallel session talk
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18. INCLUSIVE TT CROSS-SECTION
arXiv:
arXiv:
Selection : 2 opposite sign and flavor leptons, at least two jets and at least one b-tagged
Simultaneous measurement of cross- section an b-jet efficiency
Selection : 2 opposite sign leptons, at least two jets and at least one b-tagged. ETmiss > 40 GeV and Z mass veto.
Cut and count to extract cross section
Add somewhere that it is 8 TeV
4.3%
5.5%
5.7%
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19. INCLUSIVE TT CROSS-SECTION
Errors : ±5.7% (theo) vs ±3.5% (eμ) ➞ experiments challenge theory
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20. TOP POLE MASS With cross-section tt+1jet :
ATLAS-CONF
With cross-section tt+1jet :
arXiv:
Check notes
some alternative measurements (also showed in parallel sessions)
Most precise measurement are not pole mass but MC mass…
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21. TOP MASS
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22. SINGLE TOP : T-CHANNEL
Total cross-section measured with good precision.
Additionally, fiducial cross-section measurement, within detector acceptance (ATLAS), is done which allow to have reduced uncertainties.
Extraction of Vtb (σα |Vtb|2) and cross-section ratio (top/anti-top) sensitive to PDFs
arXiv:
ATLAS-CONF
Results for 7 TeV : arXiv: (ATLAS) and arXiv: (CMS)
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23. SINGLE TOP : WT PRODUCTION
ATLAS-CONF
arXiv:
A Likelihood Fit performed on the Boosted Decision Tree output (BDT) over the eμ channel and one jet (one tag) and 2 jets (at least one tag)
A Likelihood Fit performed on the BDT output over three channels (ee, μμ, eμ) and three jet selection configurations
Sistemáticos?
Significance = 4.2σ (observed)
Significance = 6.1σ (observed)
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24. SINGLE TOP : S-CHANNEL @ 8 TeV
s-channel is the most difficult to detect in LHC due to the small cross-section, needs an annihilation quark (q) – antiquark (q’).
BDT is used to improve discrimination signal to background:
A binned maximum-likelihood fit is performed on the output of the BDT to extract the signal content
Upper limit to the 95% CL :
Significance = 1. 3σ (observed) Significance = 2.1σ (observed)
arXiv:
CMS-TOP
sistemáticos, información sobre el fondo.
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25. SINGLE TOP CROSS-SECTIONS
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26. TT+V (W/Z) SM : ATLAS-CONF-2012-126 arXiv:1406.7830
3 signatures : Same sign leptons (ttW), dilepton (ttW, ttZ), trilepton (ttW,ttZ).
Multivariate analysis. Simultaneous maximum likelihood fit.
3 signatures : Same sign leptons (ttW), trilepton (ttZ), four-lepton (ttW,ttZ).
Cut based analysis. Simultaneous maximum likelihood fit.
Combined significance : 4.9σ
Combined significance : 3.7σ
SM :
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27. SUMMARY
~5 orders of magnitude
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28. SUMMARY
Electroweak and top measurements are achieving high precision :
Experimental systematics are at the level of theory uncertainty
Measurements help to constrain : MC models, QCD calculations and PDFs
Good understanding is fundamental as these processes are background to BSM searches and Higgs boson measurements.
Measuring multi-bosons is a step towards the exploration of EWSB sector BSM.
Vector boson scattering will be one of the keys in Run-2.
Many interesting results had to be left out from this presentation…
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30. LHC Data collected by experiments : 2011 – 5 fb-1 @ 7 TeV
Peak Luminosity in Run 1 :
0.75 x 1034 cm-2 s-1
For the 8 TeV data the average pileup of <μ> = 21
For comparison, future runs :
Expected for Run 2/3 :
1.5 to 2x fb-1 till 2022
HL-LHC from 2025 :
5 x 1034, 3000 fb-1
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31. WW
ATLAS-CONF
Check conf
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32. Electroweak and Top cross-sections
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33. DIFFERENTIAL TTBAR CROSS-SECTION
Selection : Lepton + jets
Measured several normalized (unfolded) differential distributions : pTt, pTtt, mtt, ytt
Reduced systematics
Compared to a variety of event generators, parton showering models, and PDFs
Alpgen (2 ⟶ describes best ytt distribution
HERAPDF gives the best overall description of the data
Other PDFs give fairly poor agreement
ATLAS : arXiv:
Add top pT plot or comment more, check CMS measurement
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34. Cross section ratios
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35. S-CHANNEL @ 8 TeV : SELECTION
arXiv:
Isolated high pT lepton
missing energy (ETmiss)
b-jet from top decay
Second b-jet, recoil against top
Cuts
1 muon or electron
pT > 30 GeV
2 b-tagged jets
additional cuts
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36. T-CHANNEL @ 8 TeV : SELECTION
ATLAS-CONF
“light” jet with high pseudo-rapidity (η)
Isolated high pT lepton
missing energy (ETmiss)
b-jet central with large momentum
Second b-jet with lower pT
Cuts
1 muon or electron
pT > 25 GeV (|η|< 2.5 )
2 jets 1 b-tagged
pT > 30 (|η|< 4.5 ) / pT > 35 GeV ( 2.75 < |η|< 3.5 )
additional cuts
ETmiss > 30 GeV,
mTW > 50 GeV,
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37. WT PRODUCTION @ 8 TeV : SELECTION
ATLAS-CONF
exactly 2 opposite charge and isolated leptons
missing energy (ETmiss), 2 neutrinos
1 b-jet from top decay
Cuts
2 leptons
eμ pair, pTl > 25 GeV
1 or 2 jets, at least one b-tag
pT > 30 GeV
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38. SINGLE TOP : T-CHANNEL Neural Network used to discriminate background.
Maximum Likelihood Fit to the output of the NN to obtain the contributions from the different processes.
Sistemáticos?
ATLAS-CONF
arXiv:
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39. BOOSTED DECISION TREE
Recover events failing cuts in a cut based analysis.
Using simulation for signal and background to compute purity.
Resulting in a weight for each event.
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