Search for MSSM Higgs at LEP
Haijun YangUniversity of Michigan, Ann Arbor
PhysicsSeminarat Univ. of Michigan
February4, 2002
OUTLINEL�
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� Introduction of MSSM
� Main Backgrounds
� L3 Analysis Procedure
� LEP CombinedResults
� Conclusions
HaijunYang Searchfor MSSM Higgsat LEP 1
Intr oductionL�
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� Minimal SupersymmetricStandardModel
Two Higgsdoublets�� 5 Higgsbosons
3 neutral(h & H CP-even,A CP-odd),
2 charged Higgs.
� NeutralHiggs- Two ComplementaryProcesses
Higgsstrahlung Pair Production
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HaijunYang Searchfor MSSM Higgsat LEP 2
Intr oductionL�
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HaijunYang Searchfor MSSM Higgsat LEP 3
Intr oductionL�
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� Parametersof theMSSM
1. Ratioof two Higgsvacuumexpectationvalues:@(A4� �2. Massof A boson:B )3. Gauginomassparameter: C �4. Scalarfermionmass:B D5. Higgsinomassparameter: E6. Higgs-sfermiontrilinear coupling: F
� ThreeBenchmarkScenarios
B � MaximalG H F E +-,:@ � I J TeV
Minimal Mixing: No mixing in stopsectorG H F E +-,:@ � K large E
HaijunYang Searchfor MSSM Higgsat LEP 4
Intr oductionL�
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� Higgsdecayinto LNML and OQPRO is dominant.
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HaijunYang Searchfor MSSM Higgsat LEP 5
Main BackgroundsL�
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HaijunYang Searchfor MSSM Higgsat LEP 6
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HaijunYang Searchfor MSSM Higgsat LEP 7
Analysis ProcedureL�
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Step2. Neural Network: Discriminant distri-butions are combinedin a neural net-work.
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HaijunYang Searchfor MSSM Higgsat LEP 8
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HaijunYang Searchfor MSSM Higgsat LEP 9
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HaijunYang Searchfor MSSM Higgsat LEP 10
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HaijunYang Searchfor MSSM Higgsat LEP 11
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HaijunYang Searchfor MSSM Higgsat LEP 12
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HaijunYang Searchfor MSSM Higgsat LEP 13
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HaijunYang Searchfor MSSM Higgsat LEP 14
Analysis ProcedureL×
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HaijunYang Searchfor MSSM Higgsat LEP 15
Analysis ProcedureL×
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àPreselectionCuts:
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HaijunYang Searchfor MSSM Higgsat LEP 16
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HaijunYang Searchfor MSSM Higgsat LEP 17
Discriminant Variables of Tau ChannelL}
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HaijunYang Searchfor MSSM Higgsat LEP 18
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HaijunYang Searchfor MSSM Higgsat LEP 19
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HaijunYang Searchfor MSSM Higgsat LEP 20
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HaijunYang Searchfor MSSM Higgsat LEP 21
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HaijunYang Searchfor MSSM Higgsat LEP 22
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HaijunYang Searchfor MSSM Higgsat LEP 23
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HaijunYang Searchfor MSSM Higgsat LEP 24
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HaijunYang Searchfor MSSM Higgsat LEP 25
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HaijunYang Searchfor MSSM Higgsat LEP 26
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HaijunYang Searchfor MSSM Higgsat LEP 27
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HaijunYang Searchfor MSSM Higgsat LEP 28
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HaijunYang Searchfor MSSM Higgsat LEP 29
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HaijunYang Searchfor MSSM Higgsat LEP 30
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HaijunYang Searchfor MSSM Higgsat LEP 31
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HaijunYang Searchfor MSSM Higgsat LEP 32
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HaijunYang Searchfor MSSM Higgsat LEP 33
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3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L÷
3L3L3L3L3L3Lø
3Lù
3L
3L4
3L3L 3L 3L3L3L3L3L3L 3L 3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L 3L3L3L 3L3L3L 3L 3L3L3L3L3
ì 4.2 > excessat68 GeVfrom L3.
But ......
HaijunYang Searchfor MSSM Higgsat LEP 34
Exclusion Limits of ChargedHiggsLõ
3Lö
3L3L3L3L�
3L
3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L÷
3L3L3L3L3L3Lø
3Lù
3L
3L4
3L3L 3L 3L3L3L3L3L3L 3L 3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L 3L3L3L 3L3L3L 3L 3L3L3L3L3
ì Br( ; < ? =A@ = 0.0), B C � 77.2(77.1)GeV.ì Br( ; < ? =A@ = 0.1), B C � 66.9(76.0)GeV.ì Br( ; < ? =A@ = 0.5), B C � 69.7(75.7)GeV.ì Br( ; < ? =D@ = 1.0), B C � 82.7(84.6)GeV.
HaijunYang Searchfor MSSM Higgsat LEP 35
LEP CombinedResultsLõ
3Lö
3L3L3L3L�
3L
3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L÷
3L3L3L3L3L3Lø
3Lù
3L
3L3L3L 3L 3L3L3L3L3L3L 3L 3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L 3L3L3L 3L3L3L 3L 3L3L3L3L3
10-7
10E -6
10-5
10E -4
10-3
10E -2
10E -1
1
60 65F
70 75 80 85G
90H
mH (GeV/c2)
1-C
Lb
Observed
Expected background
Expected signal
Br(H→I τν)=0
LEP 189-209
10E -7
10-6
10E -5
10-4
10E -3
10-2
10E -1
1
60 65F
70 75J
80G
85 90H
95H
mH (GeV/c2)
1-C
Lb
Observed
Expected background
Expected signal
Br(H→I τν)=1
LEP 189-209
ì LEP CombinedDataagreewell with SM back-grounds
HaijunYang Searchfor MSSM Higgsat LEP 36
LEP CombinedResultsLõ
3Lö
3L3L3L3L�
3L
3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L÷
3L3L3L3L3L3Lø
3Lù
3L
3L3L3L 3L 3L3L3L3L3L3L 3L 3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L 3L3L3L 3L3L3L 3L 3L3L3L3L3
0K
0.2K0.4K0.6K0.8K
1
60L
65L
70 75 80M
85M
90N
95N
charged Higgs mass (GeV/cO 2)P
Br(
H→
τν)
LEP 189-209 GeVQ
R S T U 78.6GeVat95%C.L..
HaijunYang Searchfor MSSM Higgsat LEP 37
ConclusionsLV
3LW
3L3L3L3LX
3LY
3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L3LZ
3L3L3L3L[
3L\
3L]
3L3L3L 3L 3L3L3L3L3L3L 3L 3L3L3L3L3L3L3L3L3L3L3L3L3L3L3L 3L3L3L 3L3L3L 3L 3L3L3L3L3
^ Morethan200_"`ba c datawerecollectedperexper-iment in the Year2000. In total d 700 _�`ea c werecollectedabove f g poleby eachexperiment.
R No significantevidenceof MSSM neutralandchargedHiggsareobservedup to h i 209GeV.
R NeutralHiggslimits with 95%C.L.
j k U lnmporq GeV, j s U lnmporl GeVtvuxw y
is excludedfr om 0.5to 2.4
R ChargedHiggslimits with 95%C.L.
j S T U z|{no~} GeV
HaijunYang Searchfor MSSM Higgsat LEP 38