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

Fisica ai collisionatori adronici C. Gemme (INFN Genova) Corso di Dottorato 2014. Outline del corso. Collisionatori ( adronici ) Motivazioni LHC Rivelatori ai collisionatori Anatomia del rivelatore (ATLAS) Trigger Operazione Performance. Osservabili e Analisi dati

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

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

  2. Outline del corso • Collisionatori (adronici) • Motivazioni • LHC • Rivelatoriaicollisionatori • 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: www.ge.infn.it/~gemmec/talks/Didattica/ LHCP 2014: https://indico.cern.ch/event/279518/ ICHEP 2014: http://ichep2014.es/ (this week!) ATLAS: https://twiki.cern.ch/twiki/bin/view/AtlasPublic/WebHome CMS: https://twiki.cern.ch/twiki/bin/view/CMSPublic/PhysicsResults

  3. W/Z bosons Fisica ai Collisionatori Adronici

  4. 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 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

  6. 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) 072004 • 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 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/Zis used to extrapolate the cross-section measured in the fiducial volume, σfid, to the full kinematic region: Phys. Rev. D85 (2012) 072004 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) 072004 √s = 7 TeV • Measurements already limited by sys and lumi uncertainties • Good agreement with NNLO prediction • Discriminating power against different PDF sets

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

  10. 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-13-013 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 partonradiation at large angles. Fisica ai Collisionatori Adronici

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

  13. Rare processes, an example: Z4l arXiv:1403.5657 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 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 s7/8 TeV cross sections: from 10s of fb to 10s of pb 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 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! Fisica ai Collisionatori Adronici

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

  19. 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) Fisica ai Collisionatori Adronici

  20. The big picture Fisica ai Collisionatori Adronici

  21. Top quark https://indico.cern.ch/event/279518/session/27/contribution/37/material/slides/0.pdf Fisica ai Collisionatori Adronici

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

  23. Fisica ai Collisionatori Adronici

  24. 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 Fisica ai Collisionatori Adronici

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

  26. Top decay • Each top decays ~100% tWb ~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… Fisica ai Collisionatori Adronici

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

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

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

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

  32. Top mass • Top mass world combination: mtop = 173.34 ± 0.76 GeV ATLAS-CONF-2014-008 / CDF note 11071 CMS PAS TOP-13-014 / D0 note 6416 Fisica ai Collisionatori Adronici

  33. 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. Fisica ai Collisionatori Adronici

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