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Standard Model @ Hadron Colliders III. Triple Bosons & Top Quark

Standard Model @ Hadron Colliders III. Triple Bosons & Top Quark. P.Mättig Bergische Universität Wuppertal. W mass result. D0 measurement same precision as previous world average. A huge achievement after 20 years of work ! High precision possible at proton colliders

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Standard Model @ Hadron Colliders III. Triple Bosons & Top Quark

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  1. Standard Model @ HadronCollidersIII. Triple Bosons & Top Quark P.Mättig Bergische Universität Wuppertal Peter Mättig, CERN Summer Students 2014

  2. W massresult D0 measurementsameprecision as previousworldaverage A hugeachievementafter 20 years of work! High precisionpossible at protoncolliders Importantconstraint on Standard Model Higgs Peter Mättig, CERN Summer Students 2014

  3. Into the heart of gauge theories Peter Mättig, CERN Summer Students 2014

  4. LookingforTGVs (TripleGaugeBosonVertices) W – Boson weakly and electrically charged  coupling to Z0 and g • Very fine compensation of contributions • motivation to introduce Z0 • Relates couplings to fermions and bosons First measurements at e+e- collider LEP Onset of cancellation process seen Quantify with‘anomalous couplings’ Peter Mättig, CERN Summer Students 2014

  5. Signaturesofanomalouscouplings Clearest signature in excess of events with high pT Selectionof ZW events: threehardleptons + missing ET Step1:Z0  e+e-, m+m- Step 2: transversemassStep 3: pTof Z Peter Mättig, CERN Summer Students 2014

  6. Anomalous 3 – bosoncouplings Measurements agree with Standard Model expectation Sensitivity to possible deviations at LHC approaches LEP: a few % Increased statistics and higher energies during the next years will significantly boost precision Peter Mättig, CERN Summer Students 2014

  7. Special interest: W pairsfrom VBF 1960s: event rate for WLWL WLWL explodes at 1.2 TeV Higgs boson should cure this: theory works fine Forward going jet W – boson fusion Forward going jet Require high jj mass + high |Dy| Expected background: 16.9 Expected WWjj: 15.2 Observed nb. Events: 34  Evidence for VBF Peter Mättig, CERN Summer Students 2014

  8. TestingelectroweaktheoryatLHC/Tevatron • Millionsof Z0, W±allowtightconstraints on • pdfs, strong interactions • Electroweaktheoryprobedatmulti – TeVscale: nodeviationfound • The massofthe W bosonimprovedby • factor 2 • Precision ofVectorbosonselfinteractions • (triple, quartic) will soonsuperseed LEP Peter Mättig, CERN Summer Students 2014

  9. Top quark Basic facts Peter Mättig, CERN Summer Students 2014

  10. Themysterioustopquark Top quark: no internalstructure butheavy as a gold atom i.e. couplingstrength to Standard Model HiggsBoson  l t = 0.996±0.006 Suggests a specialroleof top quark? Peter Mättig, CERN Summer Students 2014

  11. A constrainedgiant? Top quark has same role as up-quark (electron, n) ….. All are ‘matter’ particles, but • Doesthe top quarkhavethe same propertiesas light fermions? • Couplingstrengthstophotons, gluons, W – bosons? • Charge • Weakparityviolation • ....... Peter Mättig, CERN Summer Students 2014

  12. A briefhistory of thetopquark Known to existsince 1973  searchfor 20 years Phenomenologicalprejudice: around 15 GeV (ss) = 1 GeV, (cc) = 3.1 GeV, (bb) = 9.4 GeV,  (tt) = 30 GeV ?? motivationforseveralaccelerators: PETRA/PEP, TRISTAN, SppS, LEP, .... Nosignaturefound! Observed in 1995 atTevatron, a few 1000 top‘scollected LHC currentlyproduces ~ 50000 ttevents/day In netyears: close to 1M/day Peter Mättig, CERN Summer Students 2014

  13. Phenomenology of heavytop Forlighterquarks: strong interaction >> weakinteractions  colour neutral hadrons competinginteractions: who‘sfaster? t t g b b For top quark: strong interaction < weakinteractions top quarksdecaybeforehadronsformed, ‚freequark‘ Peter Mättig, CERN Summer Students 2014

  14. Phenomenology of heavytop Decayproperties of top quarkunambigouslypredictedby SM Decayfractionslargelydeterminedbyfractionsof W – decay tt (only) 6 quarks largestfraction, very high background tt  4 quarks, chargedlepton, neutrino Some 30% ‚usable‘, lowbackground FAVOURED channel tt  2 quarks, 2 charged l, 2 neutrinos Only 5% ‚usable‘, verylow background, difficult to reconstruct 99.1% of all top quarksdecayinto a bottomquark! Peter Mättig, CERN Summer Students 2014

  15. A semileptonicttevent Peter Mättig, CERN Summer Students 2014

  16. Surveyingthe top quark Peter Mättig, CERN Summer Students 2014

  17. ttCross Section Test of QCD with massive quarks Measurecouplingstrengthgtt • Event selection • 4 high pTjets • isolatedelectron/muon • missingtransverseenergy Whatfraction of tteventsareretainedafterselection Luminosity: Howmanyprotoncollisions? Peter Mättig, CERN Summer Students 2014

  18. Cross sectiondetermination Experimental precisiondepends on how well - background, efficiency, luminositycanbecontrolled Key issuedetermineefficiency • Largestuncertainties: • modellingof top • partondistributionfct. • Background yield • Jet energyscale • selectionefficienciese, m Log s ModelledpT SelectedpTrange TruejetpT Jet pt Experimental uncertainty~ 2.3% Luminosityuncertainty~ 3.1 % Total uncertainty 4.3% Beam energy~ 1.7 % Improvement by factor 2 – 3 within a year! Peter Mättig, CERN Summer Students 2014

  19. Cross sectionmeasuremnt Theoreticaluncertainty <5 % (significantimprovement last 10y) Theory & experimentuncertaintyaboutequal Verygood agreement betweendata andexpectation Peter Mättig, CERN Summer Students 2014

  20. Weightingthe top quark Peter Mättig, CERN Summer Students 2014

  21. Mass of thetopquark A fundamental parameter of the Standard Model A broadspectrum of decays and methods Note: first time a quarkmasscanbe measureddirectly (Lighterquarks to beinferredindirectlyfromhadronmasses) Peter Mättig, CERN Summer Students 2014

  22. Top massfroml+jetdecays Favouredtopology: tt 4 Jets (2 b –jets) + e/m + n • Theproblems: • How to getthe z – component of n • Out of 4 (ormore) jets: whichjetbelongs to whichtop? • Whatistheenergyscale of jets (and electrons) Peter Mättig, CERN Summer Students 2014

  23. Problem 1: pz(n) Constraintfrom W - mass Note: n – masscompletelynegligible Quadraticequation 2 solutions physics: in 70% thesolutionwithsmallerpzcorrect Peter Mättig, CERN Summer Students 2014

  24. Problem 2: whichjets? • Twofacettes: • ifmorethan 4 jets (initialstate rad.) • mostlyjetswithhighestpT • ifexactly 4 jets: whichbelongs to • whichtopquark? • 4 jets 4 possibleassigments • (jAjBJC/jD, jAjBjD/jC, ....) • Note: if b – jetsidentified, reduced to 2 possibilities • Importantconstraints • mass (jjj) = mass(jln) (= Mt) • mass (jj) = MW Peter Mättig, CERN Summer Students 2014

  25. Problem 3: jetenergyscale Measuresignals in calorimeter derivejetenergy Impliesuncertainty!  relatesdirectly to topmass • Top – quarksoffer ‚selfcalibration‘ • M(jj) has to beequal MW • change JES such thatfulfilled • Still dominant uncertaintyofMt Peter Mättig, CERN Summer Students 2014

  26. Use all information Theoreticalpredwith M1(top) Convolute with experimental effects w1 Theoreticalpredwith M2(top) w2 Sumover all events and find combineweights ...... Find M(top) withmaximumweight Recent CMS: 172.04±0.19±0.75 GeV statistical & systematicuncertainty Peter Mättig, CERN Summer Students 2014

  27. Measurements of Mtop • Combination of all measurements (March 2014) • 173.3 ± 0.3 ± 0.7 GeV • 0.4% precision! • Caveat: • Relation to ‘theoretical’ top mass somewhat uncertain • due to QCD models • Other methods developed Peter Mättig, CERN Summer Students 2014

  28. Top Quarks atHighestEnergy Top production at TeV energies: Deviations from Standard Model? Decay t bqq at high pT: quarks tend to merge in one jet Low pT selection to be modified One ‘Fat’ jet with substructures Several partons merge into a single jet Lorentz Boost Peter Mättig, CERN Summer Students 2014

  29. Searchingfor a tt - resonance tt masses up to 3 TeV well described by Standard Model strong interactions Sensitivity to new ultra - heavy particles X  tt Postulated in many BSM scenarios  at thisstage no newparticleobserved Peter Mättig, CERN Summer Students 2014

  30. Testing top quarksat LHC/Tevatron • Proton collidersonlysourceofinformation • Measurementsandtheoryofcrosssection • bynowuncertaintyof~ 5% • Top massdirectlymeasuredto 0.4% • Theoreticalinterpretationlimiting? • Top decaysandproductionshowno • deviationfrom SM expectation Peter Mättig, CERN Summer Students 2014

  31. The Higgsmechanism - basics Peter Mättig, CERN Summer Students 2014

  32. Electroweaksymmetrybreaking • Masses of bosons and fermions (w/o newmechanism) • In conflictwithlocalgaugeinvariance • Bothforfermionsandvectorbosons • Also: bosonmassesleadto • a. infinite crosssections WLWL WLWL b. or a stronglycouplingbetweenW‘s manyW‘s, ..... Way out: introduce new scalar (spin 0) particle Peter Mättig, CERN Summer Students 2014

  33. Thesolution ‚Higgsmechanism‘ • The Standard Model answer: • Higgsfields • givesmass to bosons • providesmeansforfermionmass • implieselementaryphysicalparticle • givesmass to HiggsBoson • NOTE: nopredictionofmasses! Introduce potential (by hand) Twounknowns: l, m Mass of W Mass of Higgs Mass of fermions v: ‚vacuumexpectationvalue‘ MW v = 246 GeV Peter Mättig, CERN Summer Students 2014

  34. A fewnotes on mass Mass always of basic importance B.Müller  Derek Leinweber A dynamicalgeneration of hadronmasses 99% of visible matter due to stronginteraction Thisprincipledoesnotworkifparticlesareelementary! Peter Mättig, CERN Summer Students 2014

  35. TheHiggsBoson: well known! • ..... exceptitsmass! (until 2012) • Whatis to beknown to searchfortheHiggsboson: • howisitproduced? • howstronglyisitproduced? • howdoesitdecay? • Devise searchstrategyalongthisline Peter Mättig, CERN Summer Students 2014

  36. Higgssearches at HadronColliders Peter Mättig, CERN Summer Students 2014

  37. HowtheHiggsdecays Peter Mättig, CERN Summer Students 2014

  38. Howstrongisthecoupling? Width of higgsboson proportional tocoupling G(H) ~ M(H) Threshold W/Z passed: High coupling Initial W/Z: high X-section Verysmallwidth ... Verysmallcoupling! Peter Mättig, CERN Summer Students 2014

  39. Howtointerpretthemeasurements Peter Mättig, CERN Summer Students 2014

  40. Test ifdata EXCLUDE hypothesis • Step 1: X-section at mass mHthat • canbeexcluded @ 95% CL • Step 2: Plot ratio • s(exclusion)/ • s (Xsec of SM expectation) • Ifbelow 1: • Higgsexcluded in massrange • Ifabove 1: • Higgscannotexcludedsince • either: ‚hint‘, ..... ‚signal‘ • or: no sensitivityforexclusion Compare to expectation (i.e. simulationassuming no signal) IF expectationabove SM HiggsX-section: no sensitivity to exclude IF expectationbelow BUT dataare high: a firsthint Peter Mättig, CERN Summer Students 2014

  41. 95% CL Limits ZZ  (l+l-) (l+l-) Simulation with NO signal, but luminosity, detectoreffects, ....  EXPECTED limit No sensitivity Small s*BR Oscillationsaround expectation: moreorlessevents thanbackgroundexpectation INTERESTING! Data canexcludelessthanexpected by large margin Regions of ratio < 1 EXCLUSION! Peter Mättig, CERN Summer Students 2014

  42. p - valueprobability of stat. fluctuation ‚p – value‘ : howlikelyisitthat at a certainmass MH - theexpectedbackgroundfluctuatesupward - to produce at least thenumber of observedevents Observeddearthorexcess reflected in wiggles Convention: Signal observedif p > 5s Peter Mättig, CERN Summer Students 2014

  43. Combining all searches • High massrange: • ZZ  l+l-l+l- • ZZ  l+l-nn • ZZ  l+l-qq • WW  l+nl-n Higgs EXCLUDED 2·MW < MH < 558 GeV (CMS: 600GeV) High mass Standard Model Higgsboson (almost) excluded Peter Mättig, CERN Summer Students 2014

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