1. Fisica ai collisionatori adronici
C. Gemme (INFN Genova)
Corso di Dottorato 2014

2. Outline del corso Collisionatori (adronici)
Motivazioni
LHC
Rivelatori ai collisionatori
Anatomia del rivelatore (ATLAS)
Trigger
Operazione
Performance
Osservabili e Analisi dati
Misure di standard model
Introduzione
EW: fit, W/Z, top
Higgs
Richiami teorici
La scoperta
Higgs gg
Proprieta’ dell’Higgs
Aspettative dei prossimi run
Oltre il modello standard
Supersimmetria
“Esotici”
Slides:
LHCP 2014:
ICHEP 2014: (this week!)
ATLAS:
CMS:

3. Fisica ai Collisionatori Adronici
W/Z bosons
Giugno 2014
Fisica ai Collisionatori Adronici

4. Fisica ai Collisionatori Adronici
W/Z bosons
Last time we have seen how to identify Z/W boson.
Next:
W mass
W/Z Production
W/Z + jets Production
Z4l
Diboson production
Measurement of aTGC
~20% nn , ~10% ll, 70% hadrons
~67% hadrons, ~33% ln
Giugno 2014
Fisica ai Collisionatori Adronici

5. W mass World measurement by Tevatron and LEP:
Analysis being performed with full Tevatron dataset (~10 fb-1):
CDF ~10 MeV, D0 ~ 15 MeV total uncertainty projection;
More LHC measurement to come
With MW
Without MW
Giugno 2014

6. Fisica ai Collisionatori Adronici
W/Z production
W/Z production studied (mainly) in the leptonic modes:
W boson signature (~33% lv, ~67% hadrons): one high pT lepton and missing energy
Z boson signature (~20% inv, ~10% ll, ~70% hh): two high pT opposite charge, same flavour leptons
Phys. Rev. D85 (2012)
First step is to measure the fiducial cross-section
Where N are the candidate events in data, B background events computed using data and simulation, Lint the integrated luminosity corresponding to data and trigger used. CW/Z is correction factor measuring the efficiency in the fiducial region determined by the selection cuts, for instance pT> xx GeV, etc…
NMC,rec events after simulation, reconstruction and selection
NMC,gen,cut events at the generation in the fiducial cuts
Giugno 2014
Fisica ai Collisionatori Adronici

7. W/Z production
The fiducial cross-section is dependent on the analysis cuts, therefore not very useful for comparisons with other results or theoretical expectations.
The total cross-section in the leptonic channel is instead given:
where the acceptance AW/Z is used to extrapolate the cross-section measured in the fiducial volume, σfid, to the full kinematic region:
Phys. Rev. D85 (2012)
NMC,gen,cut events at the generation in the fiducial cuts
NMC,gen,all events at the generation
√s = 7 TeV, L = 36 pb-1, electron channel
√s = 7 TeV, L = 33 pb-1, muon channel

8. W/Z production
Once the cross-sections in the electron/muon channels are measured, the ‘leptonic’ result is given, properly accounting for the common systematics errors:
Phys. Rev. D85 (2012)
√s = 7 TeV
Measurements already limited by sys and lumi uncertainties
Good agreement with NNLO prediction
Discriminating power against different PDF sets

9. Fisica ai Collisionatori Adronici
W/Z production
Total cross-section vs cms energy
Measuring the ratio between e and muon channel is a measurement of the branching ratio between the two channels
Giugno 2014
Fisica ai Collisionatori Adronici

10. Fisica ai Collisionatori Adronici
W/Z production  PDF
Cross-sections and mainly the differential cross-sections provide discrimination power for the PDFs.
Sensitive to gluon PDF
10 bins in pT(Z) and 8 bins in Y(Z): CMS PAS SMP
Giugno 2014
Fisica ai Collisionatori Adronici

11. W/Z production with jets
Production of jets in association with vector bosons allow to test pQCD
Difficult to provide NLO predictions at high multiplicities
PDFs probe region of high Q2 and low x
Important background for many searches of new physics
Sensitive to renormalization scales, PDFs and hard parton radiation at large angles.
Giugno 2014
Fisica ai Collisionatori Adronici

12. W/Z production with jets
Up to 7 jets measured (17 events)
Giugno 2014
Fisica ai Collisionatori Adronici

13. Rare processes, an example: Z4l
arXiv:
Giugno 2014
Fisica ai Collisionatori Adronici

14. Diboson production (WW,ZZ,WZ,Wg,Zg, gg)
At the LHC dibosons measurements allow Precision tests of Standard Model and searches of new physics:
The major background to many Higgs channels
Background to many BSM searches
Probes of anomalous gauge boson self-interaction
Sensitive to BSM physics
Closely related to Higgs/EWSB mechanism
The electroweak Lagrangian of the SM allows for triple gauge couplings:
Leads to two bosons in the final state
Giugno 2014
Fisica ai Collisionatori Adronici

15. Diboson production (WW,ZZ,WZ,Wg,Zg, gg)
In the boson production:
Largest LO contributions :
s-channel with triple gauge vertex
qqbar t- and u-channel (without triple coupling!)
Gluon-gluon:
typically a few % of the s 7/8 TeV cross sections: from 10s of fb to 10s of pb
Giugno 2014
Fisica ai Collisionatori Adronici

16. Anomalous Triple Gauge couplings
SM(+Higgs): Existence and strength of Triple and Quartic gauge boson couplings fully constrained
Deviations = New Physics!
However, physics beyond the SM could allow for ”anomalous” Triple Gauge Couplings (aTGCs)
Search for an excess in high energy tails where SM backgrounds are small
Giugno 2014
Fisica ai Collisionatori Adronici

17. Parametrization of aTGCs
Non-SM processes can affect TGCs:
aTGCs modify total production rate as well as event kinematics
Possible vertices using an effective Lagrangian with a parametrization:
For ZZZ and ZZg couplings (forbidden!):
For WWZ and WWg couplings:
No deviation from SM expectation found!
Giugno 2014
Fisica ai Collisionatori Adronici

18. Fisica ai Collisionatori Adronici
Diboson production
Example: measurement of ZZ production at 8 TeV
Reconstructed Z in both e+e- and m+m-
Small background contamination
Giugno 2014
Fisica ai Collisionatori Adronici

19. Fisica ai Collisionatori Adronici
Diboson production
Example: measurement of ZZ production at 8 TeV
Reconstructed Z in both e+e- and m+m-
Small background contamination
Measurements are
slightly above theory
expectations (but in
agreement within 1s)
Giugno 2014
Fisica ai Collisionatori Adronici

20. Fisica ai Collisionatori Adronici
The big picture
Giugno 2014
Fisica ai Collisionatori Adronici

21. Fisica ai Collisionatori Adronici
Top quark
Giugno 2014
Fisica ai Collisionatori Adronici

22. By Grannis, Tevatron Legacy@ LHCP2014
Giugno 2014
Fisica ai Collisionatori Adronici

23. Fisica ai Collisionatori Adronici
Giugno 2014
Fisica ai Collisionatori Adronici

24. Fisica ai Collisionatori Adronici
Top Quark is special!
Its mass is much larger than any other fermion  only quark that has weak decay in real W, rather than a virtual W.
The decay width is large: decay happens before any strong bound may be formed as happens for c and b  measure quark properties before hadronization.
Latest results:
ΔMtop/Mtop <1%
Best relative precision available for any of the quark masses
Giugno 2014
Fisica ai Collisionatori Adronici

25. Fisica ai Collisionatori Adronici
Top production
Top production at Tevatron vs LHC: complementary information!
Top-antitop
Single top
t-chan
tW-chan
s-chan
Single top quarks produced by EW interaction
has been observed at Tevatron in 2009
Giugno 2014
Fisica ai Collisionatori Adronici

26. Top decay Each top decays ~100% tWb Top pair production decays
~67% hadrons,
~33% ln
Top pair production decays

27. Top-antitop cross-sections at LHC
Cross-sections are measured in all the channels, despite the S/B being different between them.
Similar for 8 TeV, results are coming…
Giugno 2014
Fisica ai Collisionatori Adronici

28. Top-antitop cross-sections: summary
* Representative exp. uncertainty: 7 TeV;
8 TeV per experiment; 5% Tevatron
* Prediction in agreement with observed data

29. Fisica ai Collisionatori Adronici
Single top production
Small cross sections: very small yields and overwhelming background
ttbar
W+jets (t-channel) Z+jets (tW-channel)
QCD multijet, dibosons
Giugno 2014
Fisica ai Collisionatori Adronici

30. Fisica ai Collisionatori Adronici
Single top production
Small cross sections: very small yields and overwhelming background
ttbar, W/Z+ jets, QCD multijet, dibosons
Giugno 2014
Fisica ai Collisionatori Adronici

31. Single top production: Summary
No significant deviation
from SM observed
Giugno 2014
Fisica ai Collisionatori Adronici

32. Fisica ai Collisionatori Adronici
Top mass
Top mass world combination: mtop = ± 0.76 GeV
ATLAS-CONF / CDF note 11071
CMS PAS TOP / D0 note 6416
Giugno 2014
Fisica ai Collisionatori Adronici

33. Fisica ai Collisionatori Adronici
Top and calibration
Top final states involve all types of particles...
light-quark and b jets, missing transverse energy (ν), electrons, muons, tau decays products
The whole detector is involved: used for detector commissioning and calibration
Example: a method to perform a b-tagging calibration exploits the very high purity of the tt pairs with both W’s decaying leptonically.
The b-tagging efficiency can be computed either with tag-and-probe or applying b-tagging algorithm to both jets and comparison with simulation.
Giugno 2014
Fisica ai Collisionatori Adronici