23-28 July 2001 Gail G. Hanson
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Lepton Photon Symposium LP01
OUTLINE• Standard Model Higgs Search
• MSSM Higgs Search
• Non-SM Higgs Searches
• Searches for Supersymmetry
• Single Top Quark Production
• Searches for Leptoquarks
• Searches for Excited Fermions
• Technicolor Searches
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STANDARD MODEL HIGGS BOSON
10-5
10-4
10-3
10-2
10-1
1
100 102 104 106 108 110 112 114 116 118 120
mH(GeV/c2)
1-C
Lb
3σ
2σ
4σ
LEP
ObservedExpected s+bExpected b
-10
-5
0
5
10
15
20
25
100 102 104 106 108 110 112 114 116 118 120
mH(GeV/c2)
-2 ln
(Q)
Observed
Expected background
Expected signal + background
LEP
November 3, 2000, LEP Experiments Committee (LEPC) presentation:
2.9 s.d. incompatibility with background(1 - CLb) = 0.0042
23-28 July 2001 Gail G. Hanson
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Lepton Photon Symposium LP01
SM HIGGS SEARCH CHANNELS
Production from Higgsstrahlung e+ e− → H0 Z0:
e+
e−Z0∗
Z0
H0
“Four-Jet Channel:” e+ e− → H0 Z0 → bbqq
“Missing Energy Channel:” e+ e− → H0 Z0 → bbνν
“Tau Channel:” e+ e− → H0 Z0 → τ+τ−qq and qq τ+τ−
“Lepton Channel:” e+ e− → H0 Z0 → bbe+e− and bbµ+µ−
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STATISTICAL PROCEDURE
Likelihood ratio Q(mH) =
Each event is assigned a probability density si of being a signal at Higgs mass mH and a probability bi of being background.
• Each event is then assigned a weight wi = (si + bi)/ bi
• The likelihood of the sample L is the product of theweights. The logarithm is taken, and then the method islog-likelihood ratio.
Two hypotheses:Background only (CLb)Signal + background (CLs = CLs+b/CLb)
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Lepton Photon Symposium LP01
EVENT WEIGHTS AT 115 GeV
0.50.51134-jetOPAL10
0.50.41144-jetALEPH9
0.50.5115TauALEPH8
0.60.6118LeptALEPH7
0.60.51144-jetDELPHI6
0.70.41114-jetOPAL*5
0.72.1115E-missL34
0.90.91104-jetALEPH3
2.32.31134-jetALEPH2
4.74.71144-jetALEPH1
Current s/bNov. 3 s/bRec. mH (GeV)ChannelExp.
23-28 July 2001 Gail G. Hanson
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Lepton Photon Symposium LP01
10-5
10-4
10-3
10-2
10-1
1
100 102 104 106 108 110 112 114 116 118 120
mH(GeV/c2)1-
CL
b
3σ
2σ
4σ
LEP
ObservedExpected for signal+backgroundExpected for background
CURRENT COMBINED RESULTS
-10
-5
0
5
10
15
20
25
100 102 104 106 108 110 112 114 116 118 120
mH(GeV/c2)
-2 ln
(Q)
ObservedExpected backgroundExpected signal + backgroundTest signal + background
LEP
All four experiments published in 2000. L3 has alsopublished final analysis. New combination:
Maximum likelihood ratio at mH = 115.6 GeV.Probability of background fluctuation 2.1 s.d.
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0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
-15 -10 -5 0 5 10 15
-2 ln(Q)
Pro
babi
lity
den
sity Observed
Expected for backgroundExpected for signal (mH=115.6 GeV/c2)+ background
LEP
10-6
10-5
10-4
10-3
10-2
10-1
1
100 102 104 106 108 110 112 114 116 118 120
mH(GeV/c2)C
Ls
114.1 115.4
LEP
ObservedExpected forbackground
1 - CLb = 3.4%
CLs+b = 44%
mH > 114.1 GeV, 95% C.L.
(115.4 GeV expected)
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RECONSTRUCTED HIGGS MASS
Purity of selection:
Loose Medium Tight
23-28 July 2001 Gail G. Hanson
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MSSM HIGGS SEARCHESCombined LEP Experiments: mh0 > 91.0 GeV,mA0 > 91.9 GeV, 95% C.L.
0.5 < tan β < 2.4 excluded mh-max, mt <174.3GeV
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2HDM(II):
α= Higgs mixing angle1 ≤ mh0 ≤ 58 GeV and
10 ≤ mA0 ≤ 65 GeVexcluded at 95% C.L.for all α, tanβ
mh > 112.9 GeVADLO comb.
FlavourIndependent
h → γγ
mh > 108.2 GeVADLO comb.
HIGGS SEARCHES IN EXTENDEDMODELS
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SEARCHES FOR SUPERSYMMETRICPARTICLES
Gravity mediated supersymmetry breaking:
R-parity:
R-parity conservation:• SUSY particles are produced in pairs• The lightest SUSY particle (LSP) is stable
R-parity violating supersymmetry decays
Gauge mediated supersymmetry breaking:
23-28 July 2001 Gail G. Hanson
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Lepton Photon Symposium LP01
STOP AND SBOTTOM
95 GeV95 GeV56o
97 GeV97 GeV0o
θLimit for ∆M > 10 GeV
92 GeV68o
100 GeV0o
θLimit for ∆M > 10 GeV
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CHARGINOS
99
100
101
102
103
104
105
200 400 600 800 1000
√s > 206.5 GeVADLO
Mν~ (GeV)
Mχ 1+
(G
eV)
Excluded at 95% C.L.
tanβ=2 µ= −200 GeV
χ±~m > 103.5 GeV
for m > 300 GeVν~
∼
∼mχ± > 103.5 GeV
for mν > 300 GeV
23-28 July 2001 Gail G. Hanson
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LIMIT ON THE LSP MASS
20
30
40
50
60
70
80
10 20 30 40 50tanβ
Mχ lim
(G
eV/c
2 )
ADLO preliminary
A0=0, m0<1 TeV/c2
µ > 0
Excluded at 95% C.L.
Mtop= 175 GeV/c2
Mtop= 180 GeV/c2
χ0 Neutralino LSP1
Constraints in MSUGRA~
χ01
~m > 60 GeV
χ01
~m > 54 GeV~Mχ0 > 45.6 GeVMχ0 > 54 GeV
Mχ0 > 60 GeV
40
45
50
55
1 10
Higgsm0 ≤ 1 TeV/c2
mtop = 175 GeV/c2
Charginos (large m0)
Higgs
Sleptons
{
}
in the corridor
With LEP Combined results
Excluded at 95% C.L.
tanβ
mχ
(GeV
/c2 )
2 5
χ0 Neutralino LSP Constraints in MSSM1Unification at GUT Scale (CMSSM)
23-28 July 2001 Gail G. Hanson
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SINGLE TOP QUARK PRODUCTION
H1 events with isolated
leptons with large
missing pT
Flavor Changing Neutral Currents (FCNC)
CDF searched for
ISR and QCD corrections for LEP combination.
FCNC suppressed at tree level in SM (GIM mechanism).Small contributions at one-loop level. In e+e− σSM ~10−9 fb. Extended models,e.g. SUSY and multi-Higgs,can allow FCNC at tree level.
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EVENTS WITH ISOLATED LEPTONSAND LARGE MISSING pT
Primary Standard Model process is single W production
H1 electron muonobs. exp. obs. exp.
PTX<25 GeV 6 6.6 2 1.0
PTX>25 GeV 4 1.3 6 1.5
ZEUS electron muonobs. exp. obs. exp.
PTX>25 GeV 1 1.1 1 1.3
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LEPTOQUARKS
Leptoquarks carry baryonand lepton number. Scalaror vector.
F = L + 3B is preserved
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TECHNICOLOR
mπT > 89.1 (79.8) GeV
for ND = 9 (2)mπT
> 77 (62) GeV forND = 9 (2)
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SUMMARY AND CONCLUSIONS
Is there a light Higgs boson?
Will have to wait until ~ 2007 to find out
• mH > 114.1 GeV, 95% C.L., from direct search.
• “Hint” of 2 s.d. signal at mH = 115.6 GeV
Is there another mechanism for electroweak symmetrybreaking?
Will we find supersymmetry? Technicolor?
Still only questions!…..