lp01 searches new - INFN · 2001-10-20 · 23-28 July 2001 Gail G. Hanson 6 Lepton Photon Symposium...

Searches for New Particles

Gail G. HansonIndiana University

23-28 July 2001 Gail G. Hanson

2

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


3


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


4


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−


5


HIGGS CANDIDATE?


6


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)


7


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




Current s/bNov. 3 s/bRec. mH (GeV)ChannelExp.


8


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.


9


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)


10


RECONSTRUCTED HIGGS MASS

Purity of selection:

Loose Medium Tight


11


MSSM HIGGS


12


SUPERSYMMETRY PARAMETERS


13


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


14


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


15


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:


16


SUSY MAP

no


17


SEARCHES FOR SLEPTONS


18


STOP AND SBOTTOM

95 GeV95 GeV56o

97 GeV97 GeV0o

θLimit for ∆M > 10 GeV

92 GeV68o

100 GeV0o

θLimit for ∆M > 10 GeV


19


SQUARKS AND GLUINOS


20


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


21


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


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


tanβ

mχ

(GeV

/c2 )

2 5

χ0 Neutralino LSP Constraints in MSSM1Unification at GUT Scale (CMSSM)


22


R-PARITY VIOLATION

±


23


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.


24


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


25


LEPTOQUARKS

Leptoquarks carry baryonand lepton number. Scalaror vector.

F = L + 3B is preserved


26


EXCITED FERMIONS


27


TECHNICOLOR

mπT > 89.1 (79.8) GeV

for ND = 9 (2)mπT

> 77 (62) GeV forND = 9 (2)


28


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!…..

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lp01 searches new - INFN · 2001-10-20 · 23-28 July 2001 Gail G. Hanson 6 Lepton Photon Symposium...

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