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Higgs Mechanism

Higgs Mechanism. 13.9.2007 - Cyril Topfel. What to expect from this Presentation (Table of Contents). Some very limited theory explanation Higgs at LEP Higgs at the Tevatron Higgs at the LHC Conclusions. The Higgs-Mechanism. ... is responsible for the mass of massive particles

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Higgs Mechanism

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  1. Higgs Mechanism 13.9.2007 - Cyril Topfel

  2. What to expect from this Presentation (Table of Contents) • Some very limited theory explanation • Higgs at LEP • Higgs at the Tevatron • Higgs at the LHC • Conclusions

  3. The Higgs-Mechanism • ... is responsible for the mass of massive particles • ... causes the electroweak symmetry breaking • ... is the last piece of the Standard Model that hasn‘t been shown experimentally • The Higgs particle will be found at the LHC, if it exists.

  4. Some Theory Higgs-Potential Symmetric, but non-symmetric in the ground state. Non-zero vacuum expectation value: GF = 1.166 e-5 GEV-2 v = 246 GeV No constrain for  In the Higgs mass

  5. Some Theory Masses of the gauge bosons through symmetry breaking: Due to gauge invariance Fermions get their masses through Yukawa coupling with the Higgs field. The coupling strengths are free parameters. (But gtop~1, why?

  6. Higgs Production at e+e- Colliders

  7. Higgs Production at Hadron Colliders gg Fusion 10x > W/Z Fusion > (~= at low mass) H-radiation

  8. Higgs Decay Modes H mass (H) Dom. proc ~10MeV <130 GeV H->bb (ff) >130 GeV ~10MeV H->V*V # >180 GeV <GeV H->VV tt-channel not very relevant m(H)>500 ->  ~ m H->: rare decays, but clean signature #: V*V: one real and one virtual Vector Boson: W*W or Z*Z

  9. Higgs at LEP • LEP1 sensitive to: • e+e- -> (H0 -> bb) (Z0->) • e+e- -> (H0 -> bb) (Z0->l+l-) (l: e or ) • LEP2 additionally involved decay modes • e+e- -> (H0 -> bb) (Z0->qq) • e+e- -> (H0 -> ) (Z0->qq) • e+e- -> (H0 -> qq) (Z0->) BR* ETmiss ! 17% 6% leptonic! 60% Background! 10% * @ m(H) = 115 GeV

  10. Higgs @ LEP -> 3 sigma @ 115 GeV! BG (simulated) 1-sigma (BG) 2-sigma (BG) S (simulated) Q = L(s+b)/L(b) BUT: Combined data only 1.7 sigma 95% CL of Higgs mass lower bound of 114 GeV

  11. Higgs @ Tevatron

  12. Constrains on Higgs mass m(H)>114 GeV (LEP II) m(H)<166 GeV (LEP II) Results from precision electroweak measurements: M(H) = 85 (+39) (-28) GeV

  13. Higgs @ LHC Cross-sections 10 to 100 x larger at the LHC (depending on Higgs mass)

  14. Higgs @ LHC M(H)<120 GeV Signal x-secion*BR 0.36pb Dominant decay channel: H-bb (but only usable in associated production mode) Good b-tagging needed t-tagging to reduce bck BG x-secion (ttbb) 60pb -> 3.4 sigma @ 30 fb-1 M(H)<140 GeV 2 forward jets Higgs decay products in central region -> ~ 40 fb-1 needed for discovery

  15. Higgs @ LHC M(H)<150 GeV X-section * BR 50 fb, But very clean signature EM Calorimetry efficiency Crucial (ATLAS vs CMS performance) High mass: M(H)>130 GeV X-section * BR 5.7 fb, very clean signature

  16. Higgs @ LHC:Discovery potential

  17. Thank You

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