Tevatron: from the Discovery of the Top Quark to the Evidence for ...

Tevatron: from the Discovery of the TopQuark to the Evidence for the Higgs BosonDmitri Denisov, FermilabNagoya University Seminar, November 9 2012

Particle Experiments Tools - Accelerators• Accelerators are giant microscopesto study extremely small objectsWavelength=h/E beam• Accelerators are “converters” ofenergy into massCellE=mc 2Objects with masses up toE beam Mass E beamMass = 2E beam /c 2 could be createdTevatron center of mass energy is 2000 GeVProtons wavelength is ~10 -16 cmDmitri Denisov, Nagoya University 2

From Fixed Target to CollidersTevatronSppS• In late 1970’s the hunt for heavier and heavierelementary particles continued– Fixed target E cms ~ √2mE : for 100 GeV particle~5 TeV accelerator is required• Brilliant idea: use existing proton accelerators andcirculate antiprotons in the same beam pipe tocollide• Main challenge was to make enough antiprotons tohave dense particle beams– SppS and Tevatron were bornDmitri Denisov, Nagoya University 3

Tevatron: Proton-antiproton Collider• Chain of six accelerators to get to 1 TeV per beam energy• Single magnet ring – protons and antiprotons circulate in the opposite directions• Elaborate source of antiprotons – main driver of the Tevatron luminosity– Use of electron cooling of antiproton beam• Collision particles wavelength is ~10 -16 cmDmitri Denisov, Nagoya University 4

Peak Luminosity vs TimeNumber of eventsproducedN events = σ(Ε) x L2001 2011• Improvements to antiproton production and cooling increased Tevatron peak luminosity• Very high reliability: ~80% of ~24 hours stores were ended by planned termination• Average number of interactions per crossing is ~12 peak and ~6 average in 2011Dmitri Denisov, Nagoya University 5

Tevatron Data SetSep 30 th 2011: 11.9 fb -1 delivered10.7 fb -1 recordedData taking efficiency: > 90%2001 2011• Total data set is ~5 times above original Tevatron Run II goal• Detectors and accelerator components operated well till last store on September 30, 2011Dmitri Denisov, Nagoya University6

Tevatron Physics ProgramPrecision tests of the Standard Model– Weak bosons, top quark, QCD, B-physics…Search for particles and forces beyond those known– Higgs, supersymmetry, extra dimensions…Fundamental Questions Quark sub-structure? Origin of mass? Higgs? Matter-antimatter asymmetry? What is cosmic dark matter?SUSY? What is space-time structure?Extra dimensions?…Dmitri Denisov, Nagoya University 7

The CDF and DZero CollaborationsTevatron collaborations are ~1000 scientists from 26 countriesDmitri Denisov, Nagoya University8

CDF and DØ DetectorsCDFDØCDFSilicon DetectorCentral Drift ChamberCalorimetryExtended muon coverageFast electronicsSilicon Detector2 T solenoid and central fiber trackerLarge coverage muon systemFast electronicsDriven by physics goals detectors are rather “similar”:silicon, central magnetic field, hermetic calorimetry and muon systemsLayout of the hadron collider detectors have been finalized at the TevatronDmitri Denisov, Nagoya University 9

Tevatron Results25 years• Over 1000 publications in referenced journals from CDF and DØ• From discoveries of the top quark, new mesons and baryons to extremelyprecise measurements and searches for new phenomena• ~100 new results over last year alone – visit CDF and DZero Web pages– Only few highlights in this talkDmitri Denisov, Nagoya University 10

Tevatron Cross SectionsToday’s content• QCD• B Physics• Electroweak• Top Quark• The HiggsDmitri Denisov, Nagoya University11

Studies of Quantum Chromo Dynamics – QCDThe most copious physics process at hadron colliders“Rutherford experiment”pQCD matrix elementsjetParton distributionfunctions (PDFs)of the hadronsHadronization,showeringjetStrong coupling constant α s• PDFs, higher order corrections, α s measurements, production of vector bosonsand jets, direct photons, double parton interactions and many others• Understand how strong force works and to be able to predict backgrounds forprocesses with much lower cross sectionsDmitri Denisov, Nagoya University12

Inclusive JetsVarious QCD Measurements3 jets distributionsW + jetsMany important results including generators testingDmitri Denisov, Nagoya University13

α s Running at Untested Scale > 208 GeV• R 3/2 = σ 3Jet / σ 2Jet• Observable: average number of neighboringjets in ∆R (∆y-∆φ space) region less than πR ∆R = N jets (∆R) / N jets (all)Confirm strong coupling constantrunning up to 400 GeVDmitri Denisov, Nagoya University14

-quark StudiesHigh b quark cross section at Tevatron~10 -3 σ tot~10 4 b’s per second produced!Large data samples of particleswith b-quarks provide• B mesons lifetime studies• Mass spectroscopy (B c , etc.)• Studies of B s oscillations• CP violation studies• Search for new b hadrons• Search for rear decaysDmitri Denisov, Nagoya University 15

Discoveries of b-BaryonsAll b quark containing species areproduced: B ± , B 0 , B s , B c , Λ b …andmany new heavy baryons!First baryon withquarks fromall three generationsobserved!Dmitri Denisov, Nagoya University 16

DØ di-muon Charge Asymmetry• Di-muon charge asymmetryAbsl≡NN++b++b−−b−−bfor events coming from decays of mesonscontaining b quarks undergoing mixing• Standard Model predicts this asymmetry tobe very smallbA sl• Any substantial deviation of this asymmetryfrom zero will be indication of new sourceof CP violation• Measured value is 3.9σ from prediction−+NN= ( −2.3+ 0.5− .6) ×010−4Dmitri Denisov, Nagoya University 17

Di-muon Asymmetry AnomalyDecay channel for B s0 :B s0 →μ + νD s− XD s− → φπ −φ → K + K −Decay channels for B 0 :1) B 0 →μ + νD − XD − → K + π − π −• Combined DØ result– Deviation is ~2.9 σ from the SM• Reasons– New physics?– Un-known systematic?– Di-muon asymmetry is not relatedto B mesons oscillations?LHCb :B-Factories :Dmitri Denisov, Nagoya University18

Electroweak: W Boson Mass MeasurementSingle and pair W/Z production, asymmetries, weak mixing angle…M w = 80,375 23MeV0.03% accuracy• W boson mass is measured using decay products: electron and neutrino• DØ : calibration of energy scale is performed using Z boson massDmitri Denisov, Nagoya University 19

World Average W boson MassCDF: tracker based leptonmomentum measurementM w = 80,387 19 MeV0.03% accuracyW mass world average is now80,385 15 MeV (0.02%)Dmitri Denisov, Nagoya University 20

Heaviest known elementary particle:~173 GeVMeasure properties of the least knownquark• mass, charge, decay modes, etc.• data sets of 1000’s of top quarks exist Short life time: probe bare quarkTop Quark Studies85 % 15 %Discovery in 1995Today~10,000 eventsl+4 jets≥ 1 b-tagDmitri Denisov, Nagoya University 21

Discovery of the Top QuarkDue to relatively low backgrounds (high top quark mass, pair production)“a few” candidates only required for the discoveryDmitri Denisov, Nagoya University 22

Top Quark Mass Measurement• Top quark mass is measured using decay products in many different channels• Lepton+jets channel with two jets coming from W boson is the most preciseDØ and CDF combined top mass resultm t = 173.2±0.9 GeV0.5% accuracyBest (of any) quark mass measurement!Dmitri Denisov, Nagoya University 23

Anomaly in Top Quark Studies• In Standard Model, there is no asymmetry inleading order, but next to leading orderpredicts asymmetry– Positive asymmetry from box diagrams– Negative asymmetry from ISR and FSR• Forward backward asymmetry– Enhanced in some beyond standardmodels scenariousDmitri Denisov, Nagoya University24

Top Quark Forward-Backward Asymmetry• CDF l+jets (8.7 fb -1 )A FB = (16.2 ± 4.7) %Theory prediction: 6.6 %~2 σ deviation from NLOSlope of A FB (M tt )(15.6 ± 5.0) ×10 -4• DØ results (5.4 fb -1 )l+jets : A FB = 15.2 ± 4.0 %dileptons : A FB = 5.8 ± 5.1 ± 1.3%(stat.) (syst.)Combined result : 11.8 ± 3.2 %SM prediction : 4.7 %~2 σ deviation from NLO• Options• Statistics?• Not accurate enough QCD predictions?• New Physics?Dmitri Denisov, Nagoya University25

Main Top Quark Properties Measured at the Tevatron• Top quark mass: m t = 173.2±0.9 GeV (0.5% accuracy)• Are top and antitop masses the same? Test of CPT∆m=0.8± 1.9 GeV (equal to 1%)• Top quark lifetimeΓ t =1.99(+0.69/-0.55) GeV agrees with SM• Top charge |q|=2/3e to 95% C.L.• W helicity in top decay expect 70% longitudinal, 30% left-handedSM looks good• Asymmetry of top quark in p vs pbar direction expected to be a few %Anomalous asymmetry of ~15% - requires theory improvements?• Correlations of spins of top and anti-top are consistent with SM• No flavor changing neutral currents

Higgs Searches – Indirect LimitsIndirect experimental limits Precision theory fits including W bosonmass and top quark massM H

Higgs Searches Status: ~1.5 Years Ago• Higgs masses 158-173 GeV are excluded by the Tevatron• Precision measurements point to Higgs masses below ~150 GeV• LEP results indicate Higgs mass is above ~114 GeVMarch 2011Tevatron Direct Limits+ Indirect Constrains• Higgs mass was limited to 114 to 137 GeV window at 95% CL• Most probable value was… 125 GeVDmitri Denisov, Nagoya University 28

Higgs Production and Decays at the TevatronProduction cross sections in the 1 pb range for gg H in the 0.1 pb range for associatedvector boson productionDecays bb for M H < 135 GeV WW for M H > 135 GeVSearch strategy:M H 135 GeV gg H production with decay to WWMain background: electroweak WW productionDmitri Denisov, Nagoya University 29

Experimental Challenges• Probability of producing Higgs is lowN events = L x σ• High luminosity is important!• Backgrounds from Standard Modelprocesses are high– Only one out of ~10 12 collisionsmight contain Higgs• Separation of backgrounds is one of themain challenges in hunt for the HiggsMassDmitri Denisov, Nagoya University 30

Number of Higgs Events• Number of Higgs events available to CDF+DØ with the full TevatronRun II data set of 10 fb -1 at 125 GeV is ~10 3• Reconstruction/selection efficiencies– ~10% in H→bb channels and ~25% in H→WW channelsDmitri Denisov, Nagoya University 31

Higgs Search: H WW lνlν (M H >130 GeV)Search strategy:H 2 high P t leptons and missing E t WW pair comes from spin 0 Higgs:leptons prefer to point in the samedirectionνW + l +νW - l -0 jet ≥2 jetsDmitri Denisov, Nagoya University 32

Final Selection DiscriminantsMultivariate Analyses (neural networks, boosted decision trees, etc.)are used to provide a gain sensitivity beyond that obtained fromoptimized, cut-based analysisEventKinematicsTrainingBackgroundsSignalTrainingFinalMVA (NN, BDT…)Discriminantcorrelate multipleinput variablesEven for a single channel reach S/B ~1 in high discriminant region!Dmitri Denisov, Nagoya University33

CDF/D0 H→WW→lνlν LimitsLimits are presented as ration to Standard Model predictionsBoth experiments exclude Standard Model Higgs boson around 165 GeVDmitri Denisov, Nagoya University34

H→W + W - Tevatron CombinationExclude 147 < MH < 180 GeV at 95% CLDmitri Denisov, Nagoya University35

165 GeV Mass - Number of EventsEvents in all channels are sorted based on signal/background ratioNo excess observedDmitri Denisov, Nagoya University36

Low Mass Higgs Channels• Main discriminant is di-jet massfrom b-quarks pair• Elaborate b-tagging of jets• Multivariate analyses help toextract full information aboutevent kinematicDmitri Denisov, Nagoya University37

Results from DØ38ZHllbb ∫Ldt=9.7fb -1 WHlvbb ∫Ldt=9.7 fb -1 ZHvvbb ∫Ldt=9.5 fb -195% CL Exp (obs)Limit 3.7 (4.3) x SM@ MH=115 GeV95% CL Exp (obs)Limit 3.2 (3.7) x SM@ MH=115 GeV95% CL Exp (obs)Limit 3.0 (2.7) x SM@ MH=115 GeVAll channels are consistent and demonstrate sensitivity to the HiggsDmitri Denisov, Nagoya University38

Results from CDFZHllbb∫Ldt=9.5 fb -1 WHlvbb ∫Ldt=9.5 fb -1 ZHvvbb ∫Ldt=9.5 fb -12 b-tag, TT+TLx10x2095% CL Exp (obs)Limit 2.6 (4.7) x SM@ MH=115 GeV95% CL Exp (obs)Limit 2.0 (3.1) x SM@ MH=115 GeV95% CL Exp (obs)Limit 2.7 (2.7) x SM@ MH=115 GeVPattern of an excess is starting to appear…Dmitri Denisov, Nagoya University39

Cross Check on Di-boson Processes40Benchmark for Hbb searches using well known processWZ, ZZ with W or Z decaying to leptons and Z decaying to heavy flavor jetsH or ZApply exactly the same selections and multivariate analysis as for WH/ZH searchesCDF+DØ combination cross-section: 3.9 +/- 0.9 pbStandard Model prediction: 4.4 +/- 0.3 pb4.5 σ significanceDmitri Denisov, Nagoya University40

CDF and DØ Higgs Search ResultsCDF and DØ combinations of all Higgs search channels:H→WW, H→bb, H→γγ + other modesRemarkably similar shapes: no excess belowbroad excess aroundexclusion around~110 GeV~120-140 GeV~165 GeVDmitri Denisov, Nagoya University41

June 2012 Tevatron CombinationObserved LimitExpected LimitSM PredictionDmitri Denisov, Nagoya UniversitySignificant excess: at 120-135 GeV42

Excess Shape Comparable with Higgs – Yes!Injection of Standard Model Higgs signal at 125 GeV provides very similarto the observed behavior“background like” shape above ~140 GeV“signal like” shape in 115-140 GeV regionDmitri Denisov, Nagoya University43

Probability of Background to Mimic Signal3.0σ local excess at 120 GeV2.5σ global excess taking into account “look elsewhere effect”as we perform studies at many data pointsDmitri Denisov, Nagoya University44

Tevatron H→bb Combination95% CL Upper Limits/SMJuly 2012Broad excess, maximum between 120 and 140 GeVDmitri Denisov, Nagoya UniversityWidth consistent with di-jet mass resolution45

H→bb, Probability of Background to Mimic SignalJuly 2012Significance ofobservedexcessChannels Local GlobalH→bb3.3 σ3.1 σEvidence!Dmitri Denisov, Nagoya University46

Events Count for 125 GeV Higgs SearchClear excess in the high Signal/Background regionDmitri Denisov, Nagoya University47

Best Fit Cross Sections• Using data we extract σ x Br for H bb, H WW and H γγ valuesnormalized by the Standard Model predictions• All data are compatible with predictions for the Standard Model Higgs bosonDmitri Denisov, Nagoya University 48

Evidence for the Higgs Boson with Full Tevatron Data Set• Tevatron Higgs search data are incompatible with background only hypothesis• For Higgs to bb channel p-value is 3.1σ• Tevatron data are compatible with Standard Model Higgs boson production in themass range• 115 GeV < M H < 135 GeV in all studied channels including H bb, H WW and H γγ•• Based on Tevatron results, including precision W boson and top quark massmeasurements, new particle has properties predicted for the Higgs in theStandard Model and couples to fermions• All of the above is interpreted as• Evidence for the Higgs boson production at the Tevatron

Current Status of Higgs “Searches”• LHC provides large samples of Higgs bosons (x100 Tevatron cross section)– Rare and clean decay modes, like γγ can be used for searches – discovery this summer!• Tevatron, due to proton-antiproton collisions, provides unique opportunity to study mostprobable at 125 GeV decay mode: pair of b quarks and indicate coupling to fermionsCareful analysis of all available data, including cross sections at vastly differentcollision energies, demonstrates good agreement between properties of theobserved particle and predicted in the Standard Model Higgs bosonDmitri Denisov, Nagoya University 50

Self-consistency of the Standard ModelPrecision measurements of Standard Model parameters and Higgs massof ~125 GeV are in perfect agreementDmitri Denisov, Nagoya University 51

• TevatronLooking Ahead - Higgs• Improved analysis will gain another ~10% in sensitivity• HCP, Kyoto next week• Using mass constrain of 125 GeV will improve measurements ofbranching fraction to a pair of b-quarks• Measurement of Higgs couplings• LHC• More data coming: ~30 fb -1 by later this year before ~2 yearsshutdown• Sensitivity over 3 σ for majority decay modes, including fermions• Measurement of Higgs spin using large data sets• Measurement of Higgs couplings• Higgs factory• As Higgs mass is relatively low• Medium energy lepton collider will suffice• High luminosity is required for reasonable number of Higgs bosons• Exciting option widely discussedDmitri Denisov, Nagoya University52

Tevatron Highlights Summary• Tevatron experiments published over 1000 fundamental results• From the discovery of the top quark to the evidence of the Higgs bosonproduction and decay to fermions• Many extremely precise measurements of the Standard Model parameters• 100’s of searches for physics beyond Standard Model with two “clouds” remaining• Top quark forward-backward asymmetry• Anomalous di-muon asymmetry• 10 fb -1 unique proton-antiproton collisions 1.96 TeV data set is accumulated• Tevatron collaborations will publish ~150 papers in 2012 and 2013• Large number of analyses in all physics areas continue including• Unique for proton-antiproton collider measurements• Top quark mass to ~0.6 GeV accuracy and W boson mass to ~10 MeV accuracyDmitri Denisov, Nagoya University 53

Thank you for the invitation to visit Nagoya Universityand present an exciting summary of recent Tevatronresults!ありがとうございます。Dmitri Denisov, Nagoya University 54

Backup Slides

Wjj Puzzle at the Tevatron• CDF: 3.2σ peak in di-jet mass spectrum• Cross section 3.1+/- 0.8 pb• Mass 144 +/- 5 GeV• Width consistent with detectorresolution• ATLAS/CMS (pp) do not see “thebump”• Waiting for updated CDF analysisaddressing uncovered concernsDmitri Denisov, Nagoya University• DZero: good agreement withStandard Model• Exclude 3.1 pb cross section at 5 . 10 -4• 95% CL exclusion at 1.9 pb56

Cross Section * BR MeasurementJuly 2012SM Higgs @ 125 GeV:Dmitri Denisov, Nagoya University57

Higgs to γγDmitri Denisov, Nagoya University 58

Best Fit Cross SectionsDmitri Denisov, Nagoya University 59

Full Combination Events CountDmitri Denisov, Nagoya University 60

H to bb Combination Events CountDmitri Denisov, Nagoya University 61