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Martin zur Nedden, HU Berlin 1WS 2007/08: Physik am LHC
5. Higgs Searches
● The Higgs-mechanism in the SM● Yukava-coupling, masses of fermions● Higgs Production:
Searches at TEVATRON
● Higgs decay channels Coupling constants
Branching ratios
● Higgs search at the LHC
Martin zur Nedden, HU Berlin 2WS 2007/08: Physik am LHC
Higgs Mechanism in the Standard Model
• 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 physical state H remains • coupling to mass with gffH
• No prediction of Higgs mass by SM
00
2
1H
HgHff
Martin zur Nedden, HU Berlin 3WS 2007/08: Physik am LHC
Yukava coupling, Mass of Fermions
),,( 0
0L
eRRLe eeeeGL
)(22)(
0
2
1xheeee
Geeeev
GL
xhv LRRLe
LRRLe
)(2
xheev
meemL
vGm e
ee
e
mnew term in Lagrangien needed: excluded due to gauge invariance
eR(T=0, Y=-2)
eL(T=1/2, Y=-1)
h0 (T=1/2, Y=1)
igme/(2MW)igMW
W
W
(Singlet in I,Y)
choose:
Coupling to the higgs field
h0
Martin zur Nedden, HU Berlin 4WS 2007/08: Physik am LHC
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
Martin zur Nedden, HU Berlin 5WS 2007/08: Physik am LHC
Higgs-Production in Hadron-Hadron Interactions
gluon-gluon interaction (LHC/TEVATRON):big production cross section,decay in 2 gammas
gluon-gluon interaction (LHC/TEVATRON):production cross section very small
quark-antiquark interaction (TEVATRON):big production cross section at 2TeV (TEVATRON)decay: W,Z leptons
quark-quark interaction (LHC):big production cross section at 14TeV (LHC)decay: W,Z 2 γ (or leptons)
Martin zur Nedden, HU Berlin 6WS 2007/08: Physik am LHC
Higgs – Decay Channels
(H VV) ~ GF M3H
(H γγ) ~ α2 GF M3H
(H ff) ~ GF m2f MH
Martin zur Nedden, HU Berlin 7WS 2007/08: Physik am LHC
Possible Higgs Decays / coupling constants
ffH 0
WWH 0
/0 ggH
WW
f
Hff M
emg
sin2
W
WWWH
eMg
sin
WW
ZZZH
eMg
cossin
22
1
2
2
)2(228 WFWWHF
W
MGgG
M
g
Martin zur Nedden, HU Berlin 8WS 2007/08: Physik am LHC
Decay Width of Different Higgs Channels
2
3
2
22
)4
1(24
)(H
fHfFc M
mMmGNffH
)124
1()41(28
)(4
4
2
22
1
2
23
H
W
H
W
H
WHF
M
M
M
M
M
MMGWWH
)124
1()4
1(216
)(4
4
2
22
1
2
2
2
2300
H
Z
H
Z
H
Z
Z
WHF
M
M
M
M
M
M
M
MMGZZH
2
2
2
2
22
3
32
)()(32128
)(H
WW
H
qqq
q
HF
M
MI
M
mIe
MGH
Calculations in the standard model:
Martin zur Nedden, HU Berlin 9WS 2007/08: Physik am LHC
Higgs Decay Channels: Branching Ratios
Martin zur Nedden, HU Berlin 10WS 2007/08: Physik am LHC
Higgs Decay in the Standard Modell
fermions
bosons
decay width branching ratio
Martin zur Nedden, HU Berlin 11WS 2007/08: Physik am LHC
Higgs Search Strategies
bbHZpp *
Good channel for TEVATRON:
M(H) > 135 GeV: H WWM(H) < 135 GeV: H bb
gg-fusion dominant at all Higgs masses, not to separate from BG at M < 135 GeV
qq: Higgs-Strahlung: small contribution, but god to separate from BG
Martin zur Nedden, HU Berlin 12WS 2007/08: Physik am LHC
Cross Sections at TEVATRON
Martin zur Nedden, HU Berlin 13WS 2007/08: Physik am LHC
Higgs Search at TEVATRON, upper Limit
signal: 2 b-Jet + MET + 2 leptons
if M(H) > 135 GeV
Martin zur Nedden, HU Berlin 14WS 2007/08: Physik am LHC
Upper Limit for Higgs production at TEVATRON
if M(H) < 135 GeV
Martin zur Nedden, HU Berlin 15WS 2007/08: Physik am LHC
Higgs Cross Sections at LHC
gluon-gluon fusion
vector boson fusion
Martin zur Nedden, HU Berlin 16WS 2007/08: Physik am LHC
Higgs: Signal to background ratio at LHC
for M(Higgs) = 150 GeV:
S/B < 10-10
Martin zur Nedden, HU Berlin 17WS 2007/08: Physik am LHC
Higgs to 2 Z and 4 Leptons
CMS TDR
Very clean an good measurabe event signature:4 high pT leptons, 2 invariant masses at MZ
Martin zur Nedden, HU Berlin 18WS 2007/08: Physik am LHC
Gluon-Gluon Fusion to 4 Leptonen (Atlas/LHC)
Atlas TDR
invariant masse (ZZ 4 l)
Background, not todistinguish from Higgs-Signal:qq ZZ 4 leptons
Martin zur Nedden, HU Berlin 19WS 2007/08: Physik am LHC
Higgs to 2 Gamma
CMS
also very clean signature, but small cross section:2 high pT isolated EMC-clusters
Martin zur Nedden, HU Berlin 20WS 2007/08: Physik am LHC
Gluon/Gluon Fusion to 2 Gamma (Atlas/LHC)
ATLAS TDR
Background:Not reducable: pp γγXReducable: pp γJγJ
Martin zur Nedden, HU Berlin 21WS 2007/08: Physik am LHC
Vector-Boson Fusion: Decay to 2 W-Bosons
H WW e
Atlas TDRH WW l l υ υ (l υ qq )
Signature:Jets + 2 high pT leptons + MET
No mass peak (MET from neutrino), calculate the transverse mass
Background:tt, Wt, WWJJ production
Martin zur Nedden, HU Berlin 22WS 2007/08: Physik am LHC
Higgs to 2 Tau
H ττ e :
H ττ l l + 4ν (l +J +3ν)
Atlas TDR
2 high pT leptons, big MET
Mass reconstruction possible, even with high MET
Background:Zjj , tt
Martin zur Nedden, HU Berlin 23WS 2007/08: Physik am LHC
Higgs Discovery potential of LHC/ATLAS
Dependency on Higgs mass and decay channel
Martin zur Nedden, HU Berlin 24WS 2007/08: Physik am LHC
Discovery potential of ATLAS/LHC
Dependency of Higgs-mass and Luminosity
LEP2 excluded