The Higgs Boson Beate Heinemann, University of Liverpool  The Standard Model and Beyond  Tevatron and LHC  Tevatron Results on Higgs Searches  Future Perspectives: Tevatron and LHC  Summary September 7th 2004, University of Liverpool

Beate Heinemann - Liverpool University2 -3 generations of quarks and leptons interact via exchange of gauge bosons: -Electroweak SU(2)xU(1): W, Z,  -Strong SU(3): g -Electroweak symmetry breaking caused by Higgs field -Gives masses to SM particles -Preserves unitarity -Standard Model survived all experimental challenges in past 30 years! -electroweak and QCD precision data -No New Physics yet ParticleMass (GeV/c 2 ) Force Photon (  )0Electroweak W±W± Electroweak Z0Z Electroweak Gluons (g)0Strong Gauge Bosons Higgs Boson -Vacuum quantum numbers (0 ++ ) -Couples to mass -M h = ? The Standard Model of Particle Physics

Beate Heinemann - Liverpool University3 Why not the Standard Model?  Radiative corrections to Higgs mass: electroweak scale (100 GeV) much much lower than Planck Scale (10 19 GeV): “hierarchy” or “naturalness” problem  No unification of forces at any scale  No explanation for matter/ anti- matter asymmetry in universe  “Our” universe makes only 4% or total oNo accounting for dark matter in universe: “Best” theories (SUSY) that predict Dark Matter candidate involve Higgs oIs Higgs field related to Dark Energy? WMAP satellite EM WEAK Coupling constants

Beate Heinemann - Liverpool University4 The Higgs boson: the missing piece?  Precision measurements of oM W = ± GeV/c 2 oM top = GeV/c 2  Prediction of higgs boson mass within SM due to loop corrections oMost likely value: 114 GeV  Direct limit (LEP): m h >114.4 GeV m W depends on m t and m h

Beate Heinemann - Liverpool University5  Precision measurements of oM W = ± GeV/c 2 oM top = GeV/c 2  Prediction of higgs boson mass within SM due to loop corrections oMost likely value: 114 GeV  Direct limit (LEP): m h >114.4 GeV The Higgs boson: what do we know? Better prediction with expected improvements on W and top mass precision

Beate Heinemann - Liverpool University6 What if there is no Higgs? -WW cross section would violate unitarity since amplitude perturbative expansion in energy (s):  ~s 2 /v 2 + s 4 /v 4 … -Need either a Higgs boson with m h <1 TeV or some new physics (e.g. SUSY, Technicolor) -Tevatron and LHC probe relevant scale of 100 GeV - 1 TeV! => We will find something (higgs or more extraodinary) in the next 10 years!

Beate Heinemann - Liverpool University7 Tevatron Run II  Upgrade completed in 2001  Accelerator:  Experiments CDF and D0: oNew tracking systems oNew RO electronics+trigger oMany other substantial new components and upgrades oData taking efficiency>85% √s(TeV)  t(ns)L(cm -2 s -1 ) Run II x10 32

Beate Heinemann - Liverpool University8 Tevatron and CDF Performance ∫ Ldt= 680 pb -1 Max. L=1.03x10 32 cm -2 s -1

Beate Heinemann - Liverpool University9 Tevatron and CDF Performance ∫ Ldt= 680 pb -1 Max. L=1.03x10 32 cm -2 s -1

Beate Heinemann - Liverpool University10 Beyond the Tevatron: LHC  pp-collider at CERN/Geneva  Center-of-mass energy: 14 TeV  Starts physics in 2008  Collisions: every 25 ns  3 years “low” luminosity: 10 fb -1 /yr  High luminosity: 100 fb -1 /yr  Experiments: ATLAS, CMS, LHCb

Beate Heinemann - Liverpool University11 Higgs Production: Tevatron and LHC Dominant Production: gg-> H, subdominant: HW, Hqq LHC Tevatron

Beate Heinemann - Liverpool University12 Higgs boson decay  Depends on Mass  M<130 GeV: obb dominant  subdominant  used at LHC  M>130 GeV oWW dominant oZZ cleanest

Beate Heinemann - Liverpool University13 WW Production  Motivation: oSensitive to WW  and WWZ vertex oHiggs discovery channel oAnything new/unexpected?  2 leptons +E T +no jet with E T >15 GeV: oObserved: 17 events oExpected: 16.1 ± 1.6

Beate Heinemann - Liverpool University14  Higgs mass reconstruction not possible due to two neutrions  Employ spin correlations to suppress WW background:   ll is particularly useful  Leptons from H  WW ( * )  l + l - tend to be collinear H  WW  l + l - W+W+ e+e+ W-W- e-e- n  ll between leptons

Beate Heinemann - Liverpool University15 WZ and Wh Production RunI:0.5-1%  Large backgrounds from QCD processes: W+jets, Z+jets  Use bb channel for Higgs search  WZ will be observable before seeing the higgs=> excellent calibration channel  Exercises mass resolution: combining calorimeter and tracking => 30% improvement in energy resolution

Beate Heinemann - Liverpool University16 Wh Production: Run 2 data  Selection: oW(  or e ) o2 jets: 1 b-tagged  Search for peak in dijet invariant mass distribution  No evidence yet for WZ or Wh m bb (GeV/c 2 )

Beate Heinemann - Liverpool University17 Wh Production: Run 2 data  Selection: oW(  or e ) o2 jets: 1 b-tagged  Search for peak in dijet invariant mass distribution  No evidence yet for WZ or Wh  Upper limit on Wh production cross section

Beate Heinemann - Liverpool University18 Summary of CDF Higgs Searches

Beate Heinemann - Liverpool University19 Higgs Discovery at Tevatron?

Beate Heinemann - Liverpool University20 Higgs Discovery at Tevatron? 2006

Beate Heinemann - Liverpool University21 Higgs Discovery at Tevatron? 2009

Beate Heinemann - Liverpool University22 Higgs Discovery at the LHC? fb LHC: ATLAS Values for single experiment time

Beate Heinemann - Liverpool University23 Summary  Higgs boson crucial to particle physics: oDoes it exist? oIs it the Standard Model Higgs? oIs it related to Dark Matter and/or Dark Energy? oIs it related to matter-antimatter asymmetry?  Tevatron Run II had first look for Higgs boson oData not yet sensitive to Standard Model  Tevatron and/or LHC by 2010 oWill give conclusive results on Higgs oAre likely to discover new Physics oElse, serious breakdown of particle physics theory!

Beate Heinemann - Liverpool University24 What is beyond the Standard Model?  Large creativity amongst theoretical community: oSupersymmetry (SUSY): rather complex (>100 parameters) oExtra Dimensions oTechni- and Topcolor oLittle Higgs, Extended Gauge Groups Z’,W’ oComposite particles excited fermions, leptoquarks, …  All predict new particles: oDirect production at high energy colliders oIndirect contributions to SM processes