5. Higgs Searches. The Higgs-mechanism in the SM Yukava-coupling, masses of fermions Higgs Production: Higgs decay channels. Higgs search at the LHC

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1 5. Higgs Searches The Higgs-mechanism in the S Yukava-coupling, masses of fermions Higgs Production: Searches at TEVATRON Higgs decay channels Coupling constants Branching ratios Higgs search at the LHC WS 007/08: Physik am LHC 1

2 Higgs echanism in the Standard odel Doublet Φ of scalar Higgs fields H(x) exists due to the massive gauge field W,Z and the massless γ Complex fields Φ+, Φ0 4 real components Φ1, Φ4, produce mass in symmetry breaking due to self-interaction Goldstone/Higgs-mechanism: 3 components absorbed in the longitudinal polarization of the massive 3 Wi-bosons 1 1 physical state H remains H= Φ0 Φ0 coupling to mass with gffh No prediction of Higgs mass by S f fh ( g WS 007/08: Physik am LHC ) ΨΨ H

3 Yukava coupling, ass of Fermions m ΨΨ new term in Lagrangien needed: [ ] Φ + L G ( υe, e L 0 er + er Φ, Φ 0 Φ [ ] ν e ) e L W er(t=0, Y=-) igme/(w) excluded due to gauge invariance el(t=1/, Y=-1) (Singlet in I,Y) Coupling to the higgs field W igw h0 h0 (T=1/, Y=1) ( ) ( ) 1 0 Ge Ge Φ= L v e e + e e el er + er el h( x) L R R L v + h( x ) choose: Gev me me L me ee eeh( x) v WS 007/08: Physik am LHC 3

4 Consequences from Yukava-Coupling electron gets mass neutrino rest massles strength of coupling proportional to the mass of the fermion mass is not predicted by the theory masses for quarks: same formalism as for leptons difference: both quarks within the doublet have mass new Higgs Doublet Φc WS 007/08: Physik am LHC 4

5 Higgs-Production in Hadron-Hadron Interactions gluon-gluon interaction (LHC/TEVATRON): big production cross section, decay in gammas gluon-gluon interaction (LHC/TEVATRON): production cross section very small quark-antiquark interaction (TEVATRON): big production cross section at TeV (TEVATRON) decay: W,Z leptons quark-quark interaction (LHC): big production cross section at 14TeV (LHC) decay: W,Z γ (or leptons) WS 007/08: Physik am LHC 5

6 Higgs Decay Channels Γ(H ff) ~ GF mf H Γ(H VV) ~ GF 3H Γ(H γγ) ~ α GF 3H WS 007/08: Physik am LHC 6

7 Possible Higgs Decays / coupling constants gf fh = H f f 0 + H W W 0 H gg / γγ 0 em f W sin ϑw gwwh e W = sin ϑw g ZZH e Z = sin ϑw cosϑw 1 g GF = gwwh = ( GF ) W 8 W WS 007/08: Physik am LHC 7

8 Decay Width of Different Higgs Channels Calculations in the standard model: Γ( H f f ) = Nc GF m f H 4π 3 H (1 W H 4m f H ) G 4 1 W W Γ ( H W +W ) = F (1 4 ) (1 + ) 4 H H 8π G 4 4 Γ ( H Z 0 Z 0 ) = F H W (1 Z ) (1 Z + 1 Z4 ) H H H 16π Z q H m α GF Γ ( H γγ ) = Σ 3eq I q ( ) + IW ( ) 3 18π q 3 H WS 007/08: Physik am LHC W H 8

9 Higgs Decay Channels: Branching Ratios WS 007/08: Physik am LHC 9

10 Higgs Decay in the Standard odell branching ratio decay width fermions bosons WS 007/08: Physik am LHC 10

11 Higgs Search Strategies Good channel for TEVATRON: * pp Z H ν ν bb (H) > 135 GeV: H WW (H) < 135 GeV: H bb gg-fusion dominant at all Higgs masses, not to separate from BG at < 135 GeV qq: Higgs-Strahlung: small contribution, but god to separate from BG WS 007/08: Physik am LHC 11

12 Cross Sections at TEVATRON WS 007/08: Physik am LHC 1

13 Higgs Search at TEVATRON, upper Limit if (H) > 135 GeV signal: b-jet + ET + leptons WS 007/08: Physik am LHC 13

14 Upper Limit for Higgs production at TEVATRON if (H) < 135 GeV WS 007/08: Physik am LHC 14

15 Higgs Cross Sections at LHC gluon-gluon fusion vector boson fusion WS 007/08: Physik am LHC 15

16 Higgs: Signal to background ratio at LHC for (Higgs) = 150 GeV: S/B < WS 007/08: Physik am LHC 16

17 Higgs to Z and 4 Leptons CS TDR Very clean an good measurabe event signature: 4 high pt leptons, invariant masses at Z WS 007/08: Physik am LHC 17

18 Gluon-Gluon Fusion to 4 Leptonen (Atlas/LHC) invariant masse (ZZ 4 l) Atlas TDR Background, not to distinguish from Higgs-Signal: qq ZZ 4 leptons WS 007/08: Physik am LHC 18

19 Higgs to Gamma CS also very clean signature, but small cross section: high pt isolated EC-clusters WS 007/08: Physik am LHC 19

20 Gluon/Gluon Fusion to Gamma (Atlas/LHC) Background: Not reducable: pp γγx Reducable: pp γjγj ATLAS TDR WS 007/08: Physik am LHC 0

21 Vector-Boson Fusion: Decay to W-Bosons H WW l l υ υ (l υ qq ) Atlas TDR Signature: Jets + high pt leptons + ET No mass peak (ET from neutrino), calculate the transverse mass Background: tt, Wt, WWJJ production H WW eµ WS 007/08: Physik am LHC 1

22 Higgs to Tau Atlas TDR H ττ e µ: H ττ l l + 4ν (l +J +3ν) high pt leptons, big ET ass reconstruction possible, even with high ET Background: Zjj, tt WS 007/08: Physik am LHC

23 Higgs Discovery potential of LHC/ATLAS Dependency on Higgs mass and decay channel WS 007/08: Physik am LHC 3

24 Discovery potential of ATLAS/LHC Dependency of Higgs-mass and Luminosity LEP excluded WS 007/08: Physik am LHC 4