1. 1 Higgs Mechanism 13.9.2007 - Cyril Topfel

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

5. 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 g top ~1, why?

6. 6 Higgs Production at e+e- Colliders

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

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

9. 9 Higgs at LEP LEP1 sensitive to: e + e - -> (H 0 -> bb) (Z 0 -> ) e + e - -> (H 0 -> bb) (Z 0 -> l + l - ) ( l : e or  ) LEP2 additionally involved decay modes e + e - -> (H 0 -> bb) (Z 0 ->qq) e + e - -> (H 0 ->  ) (Z 0 ->qq) e + e - -> (H 0 -> qq) (Z 0 ->  ) ET miss ! leptonic ! BR* * @ m(H) = 115 GeV 17% 6% 60% 10% Background!

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

11. 11 Higgs @ Tevatron

12. 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. 13 Higgs @ LHC Cross-sections 10 to 100 x larger at the LHC (depending on Higgs mass)

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

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

16. 16 Higgs @ LHC: Discovery potential

17. 17 Thank You