HiggsHiggs SearchesSearches atat thethe TevatronTevatron andand LHCLHC John Womersley DØ Experiment Department Fermi National Accelerator Laboratory, Batavia, Illinois http://d0server1.fnal.gov/projects/presentations/womersley/win02/win02.pdf John Womersley TheThe HiggsHiggs MechanismMechanism • In the Standard Model mass = 80.4 GeV – Electroweak symmetry breaking photon occurs through introduction of a W mass = 0 scalar field φ→masses of W and Z – Higgs field permeates space with a finite vacuum expectation value = 246 GeV – If φ also couples to fermions → generates fermion masses • An appealing picture: is it correct? – One clear and testable prediction: there exists a neutral scalar particle which is an excitation of the Higgs field – All its properties (production and decay rates, couplings) are fixed except its own mass Highest priority of worldwide high energy physics program: find it! John Womersley SearchingSearching forfor thethe HiggsHiggs 113 GeV 200 GeV • Over the last decade, the focus has been on experiments at the LEP e+e– collider at CERN – precision measurements of parameters of the W and Z bosons, combined with Fermilab’s top quark mass measurements, set an upper limit of mH ~ 200 GeV – direct searches for Higgs production exclude mH < 113 GeV • Summer and Autumn 2000: Hints of a Higgs? – the LEP data may be giving some indication of a Higgs with mass 115 GeV (right at the limit of sensitivity) – despite these hints, CERN management decided to shut off LEP operations in order to expedite construction of the LHC “The resolution of this puzzle is now left to Fermilab's Tevatron and the LHC.” – Luciano Maiani John Womersley TheThe FermilabFermilab TevatronTevatron ColliderCollider Chicago ↓ p p 1.96 TeV Booster CDF p CDF DØ Tevatron p p source Main Injector & Recycler DØ John Womersley CDF installing silicon tracker, prior to detector roll-in John Womersley DØ detector installed in the Collision Hall, January 2001 John Womersley WW→→ eeνν candidatescandidates CDF DØ mT CDF DØ 30 DØ 25 mT -1 20 ~ 700 nb 15 EM cluster 10 with track 5 0 0 20 40 60 80 100 120 140 160 2 Transverse Mass (GeV/c ) E = 48 GeV John Womersley ZZZZ →→ →→eeeeee+ee -candidatescandidatescandidatescandidates CDF CDF 24 22 20 DØ 18 16 14 12 10 DØ 8 6 4 2 0 40 60 80 100 120 140 invariant mass (GeV/c 2) (uncalibrated energy scale) John Womersley JetsJets Run 131957 Event 4781549 Wed Nov 14 17:33:47 2001 Bins: 1097 E_t: 0.0062 3 Mean: 0.405 phi_t: 160deg Rms: 2.88 DØ 10 | η| < 0.5 Min: 0.00188 Max: 52.4 -1 2-jet event 2 L3_CJT10, L = 0.004 pb 10 -1 [nb/GeV] L3_CJT15, L = 0.08 pb η d -1 T 10 L1_CJT40, L = 0.8 pb 55 jet1 •ET ~230 GeV •Ejet2 ~190 GeV 1 ET GeV T dN/Ldp DØ -1 10 PRELIMINARY 2PI -3.7 -2 10 -1.2 ! phi 0.0 -3 eta 1.2 10 0.0 -4 3.7 10 -5 10 0 50 100 150 200 250 300 350 400 p [GeV] CDF T 3-jet event Jet cross section as a jet1 function of ET, for |η| < 0.5 •ET ~180GeV R=0.7 Cone Algorithm with Run 1 corrections John Womersley TrackingTracking CDF COT DØ Fiber Tracker John Womersley MuonsMuons CDF: Z →µ+µ- candidate in muon system and COT Mµµ = 88 GeV µµ Invariant Mass (p >5, |η|<2.1) T Constant = 19.36± 2.013+ - 2 DØ: ConstantJ/ψ→µ * x = -1.38± 0.2102µ Constant * x^2 = 0.02648± 0.005284 140 candidates in G Norm = 125.4± 7.533 120 the forwardG Mean = 3.57± 0.04854 G Sigma = -0.9509± 0.05331 100 region Events per 0.5 Gev/c 80 1059 events 60 40 20 0 0 5 10 15 20 25 302 Mass (GeV/c ) John Womersley SiliconSilicon DetectorsDetectors andand bb--taggingtagging CDF B-lifetime from B → J/ψ events Consistent with world average K0 signal Silicon Stand-alone DØ tracking John Womersley HiggsHiggs atat thethe TevatronTevatron • The search for the mechanism of EWSB motivated the supercolliders (SSC and LHC) • After the demise of the SSC, there was a resurgence of interest in what was possible with a “mere” 2 TeV – Ideas from within accelerator community (“TeV33”) – Stange, Marciano and Willenbrock paper 1994 – TeV2000 Workshop November 1994 – Snowmass 1996 – TeV33 committee report to Fermilab director – Run II Higgs and Supersymmetry Workshop, November 1998 • Consensus resulted from a convergence of – technical ideas about possible accelerator improvements – clear physics motivation for integrated luminosities, before LHC turn-on, much larger than the (then) approved 2fb-1 John Womersley HiggsHiggs decaydecay modesmodes • The only unknown parameter of the SM Higgs sector is the mass • For any given Higgs mass, the production cross section and decays are all calculable within the Standard Model One Higgs H →bb H → WW John Womersley HiggsHiggs ProductionProduction atat thethe TevatronTevatron • Inclusive Higgs cross section is quite high: ~ 1pb – for masses below ~ 140 GeV, the dominant decay mode H → bb is swamped by background – at higher masses, can use inclusive production plus WW decays • The best bet below ~ 140 GeV appears to be associated production of H plus a W or Z – leptonic decays of W/Z help give the needed background rejection – cross section ~ 0.2 pb H →bb H → WW Dominant decay mode John Womersley mm << 140140 GeV:GeV: HH →→bbbb H ~~ • WH → qq’bb is the dominant decay mode but is overwhelmed by QCD background • WH → l±ν bb backgrounds Wbb, WZ,tt, single top • ZH → l+l- bb backgrounds Zbb, ZZ,tt • ZH →ννbb backgrounds QCD, Zbb, ZZ,tt – powerful but requires relatively soft missing ET trigger (~ 35 GeV) mH = 120 GeV bb mass resolution Directly influences signal significance Z →bb will be a calibration Z Higgs CDF Z →bb in Run I DØ simulation for 2fb-1 2 × 15fb-1 (2 experiments) John Womersley pp → WH Missing ET →bb → eν EM cluster Electron Track p →←p Hits in Silicon Tracker Two b-jets from (for b-tagging) Higgs decay Calorimeter DØ Towers John Womersley JustJust forfor funfun .. .. .. DØ W + 2 jet (Higgs!) candidate, October 2001 Jet 1 raw ET = 17 GeV* Electron Electron Jet 1 Jet 2 raw Jet 2 ET = 13 GeV* * Jet ET corrections will be large John Womersley Example:Example: mmH == 115115 GeVGeV • ~ 2 fb-1/expt (2003): exclude at 95% CL Every factor of • ~ 5 fb-1/expt (2004-5): evidence at 3σ level two in luminosity yields a lot -1 • ~ 15 fb /expt (2007): expect a 5σ signal more physics • Events in one experiment with 15 fb-1: Mode Signal Background S/√B lνbb 92 450 4.3 ννbb 90 880 3.0 llbb 10 44 1.5 • If we do see something, we will want to test whether it is really a Higgs by measuring: – production cross section – Can we see H → WW? (Branching Ratio ~ 9% and rising w/ mass) – Can we see H →ττ? (Branching Ratio ~ 8% and falling w/ mass) – Can we see H→γγ? (not detectable for SM Higgs at the Tevatron) John Womersley AssociatedAssociated productionproductiontttt ++ HiggsHiggs • Cross section very low (few fb) but signal:background good • Major background istt + jets • Signal at the few event level: 15fb-1 (one experiment) H →bb H → WW Tests top quark Yukawa coupling John Womersley mm >> 140140 GeVGeV :: HH → WWWW(**) H ~~ → • gg → H → WW(*) → l+l- νν Backgrounds Drell-Yan, WW, WZ, ZZ, tt, tW, ττ Initial signal:background ratio ~ 10-2 – Angular cuts to separate signal from “irreducible” WW background 2 × 15fb-1 (2 experiments) Higgs signal Background (mainly WW) Before tight cuts: After tight cuts verify WW modelling MC = cluster transverse mass John Womersley TevatronTevatron HiggsHiggs massmass reachreach mH probability density, J. Erler -1 15 fb (hep-ph/0010153) 110-190 GeV No guarantee of success, but certainly a most enticing possibility John Womersley IndirectIndirect ConstraintsConstraints onon HiggsHiggs MassMass • Future Tevatron W and top mass measurements, per experiment ∆mW 2 fb-1 ±27 MeV 15 fb-1 ±15 MeV ∆mt 2fb-1 ±2.7 GeV 15 fb-1 ±1.3 MeV Impact on Higgs mass fit using ∆mW = 20 MeV, ∆mW = 1 GeV, ∆α = 10-4, current central values M. Grünewald et al., hep-ph/0111217 M. Schmitt’s talk in the parallel session John Womersley TheThe LargeLarge HadronHadron ColliderCollider Lake Geneva ↓ CMS ATLAS SPS ATLAS Main CERN site p p CMS 14 TeV John Womersley HiggsHiggs atat LHCLHC • Production cross section and luminosity both ~ 10 times higher at LHC than at Tevatron – Can use rarer decay modes of Higgs John Womersley “Precision“Precision Channels”Channels” H →γγ H → ZZ(*) → 4l -1 -1 for mH = 120 GeV, 100fb , CMS for mH = 300 GeV, 10fb , ATLAS • Both LHC detectors have invested heavily in precision EM calorimetry and muon systems in order to exploit these channels John Womersley AssociatedAssociated productionproductionttHttH atat LHCLHC John Womersley VectorVector bosonboson fusionfusion channelschannels • Use two forward jets to “tag” the VB fusion process – Improves the S/B for large Higgs masses Two jets with E ~ 300 GeV and 2 < |η| < 4 • Example: H → WW → lνjj ATLAS Also useful for lower mH = 600 100fb-1 Higgs masses: H →ττ mH = 120 GeV ATLAS John Womersley LHCLHC DiscoveryDiscovery PotentialPotential • Significance for 100 fb-1 • Luminosity required for 5σ The whole range of SM Higgs masses is covered John Womersley SMSM HiggsHiggs parameterparameter determinationdetermination atat LHCLHC Mass Width σ·B σ·B measured to the 0.1% to 1% accuracy 5 to 10% measurement level of the luminosity in measurement of m of the width for m >300 GeV H H uncertainty (~5%?) ATLAS TDR John Womersley HiggsHiggs couplingcoupling measurementsmeasurements • Can measure various ratios of Higgs couplings and branching fractions by comparing rates in different processes • CMS estimates of uncertainties with 300 fb-1 Luminosity uncertainties largely cancel in ratios Errors are dominated by statistics of the rarer process John Womersley SupersymmetricSupersymmetric