Search for Exotica Search for Exotica (Preliminary Exotica results - - PowerPoint PPT Presentation

Search for Exotica Search for Exotica

(Preliminary (Preliminary Exotica results Exotica results up to up to √ √s=209 s=209 GeV GeV from the from the LEP LEP experiments experiments) )

Javier Cuevas Javier Cuevas University of Oviedo University of Oviedo

Topical Seminar on the Legacy of LEP and SLC Topical Seminar on the Legacy of LEP and SLC Siena, 8 Siena, 8-

• 11 October 2001

11 October 2001

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Outline Outline

• LEP

LEP EXOTICA WG EXOTICA WG: Combination of all non : Combination of all non-

• Higgs

Higgs and non and non-

• SUSY searches at LEP2.

SUSY searches at LEP2.

• Data Samples used:

Data Samples used: – – About 2.4 fb About 2.4 fb-

• 1

1 (~600 pb

(~600 pb-

• 1

1 per experiment) at

per experiment) at √s √s =189 =189-

• 209

209 GeV GeV

• Statistical procedure adopted for the combination of

Statistical procedure adopted for the combination of the different channels (same or different the different channels (same or different experiments), is the experiments), is the likelihood ratio method likelihood ratio method

• Technicolor

Technicolor

• Excited leptons

Excited leptons

• Single top production, FCNC

Single top production, FCNC

• Leptoquarks

Leptoquarks

• Gravity in extra dimensions

Gravity in extra dimensions

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Technicolor model Technicolor model

• Technicolor Model

Technicolor Model is an alternative to the Standard is an alternative to the Standard Model Mechanism of Electroweak symmetry breaking. Model Mechanism of Electroweak symmetry breaking.

• Role of Higgs boson is performed by bound states of

Role of Higgs boson is performed by bound states of new fundamental fermions, new fundamental fermions, techniquarks techniquarks, which mix , which mix with W and Z and generate their masses. with W and Z and generate their masses.

• Minimal TC

Minimal TC model with one doublet of TC model with one doublet of TC-

• quarks is

quarks is not not confirmed confirmed by LEP1 and elsewhere precision by LEP1 and elsewhere precision measurements measurements

• Extensions of TC

Extensions of TC model with many doublets, model with many doublets, Walking Walking Technicolor Technicolor, overcome disagreement with experimental , overcome disagreement with experimental

• results. A
• results. A large number of doublets

large number of doublets is required, which is required, which generate generate huge number of bound states huge number of bound states. .

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Technicolor model Technicolor model

• These extensions call for a

These extensions call for a large number N large number ND

D of

• f

technidoublets technidoublets (T (TU

U, T

, TD

D), with Q

), with QU

U=Q

=QD

D+1

+1

• Important simplification

Important simplification: : “ “Technicolor Straw Man Technicolor Straw Man Model Model” ” the lowest lying bound states of the lightest the lowest lying bound states of the lightest technifermion technifermion model model can be considered in isolation can be considered in isolation. .

– – Pseudoscalars Pseudoscalars: : Π ΠT

T±, ±,0 0,

, Π ΠT

T’ ’

– – Vectors: Vectors: ρ ρT

T±, ±,0 0 ,

, ω ωT

T (nearly mass degenerate)

(nearly mass degenerate)

• Scalar bound states are mixtures of

Scalar bound states are mixtures of W WL

L± ±, Z

, ZL

L0 0, and

, and the lightest the lightest mass mass-

• eigenstate

eigenstate technipions technipions π πT

T± ± π

πT

T0

| |Π ΠΤ

Τ >

> = = sin sin χ χ |W |WL

L> +

> + cos cos χ χ | |π πT

T>

>

• Mixing angle

Mixing angle χ χ is related with the number of TC is related with the number of TC-

• doublets:

doublets: sin sin2

2χ

χ=1/N =1/ND

D

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Decays of Decays of ρ ρT

T

• The dominant decay modes of the

The dominant decay modes of the ρ ρT

T mediated by the TC

mediated by the TC interaction are: interaction are:

• In addition the

In addition the ρ ρT

T decays

decays via the electroweak interaction via the electroweak interaction either into either into one

• ne technipion

technipion and a SM gauge boson and a SM gauge boson or into a

• r into a

pair of SM fermions pair of SM fermions ( (becomes important if other decay becomes important if other decay channels are channels are kinematically kinematically closed closed) )

• Total width

Total width depends on many parameters but does not depends on many parameters but does not exceed exceed ~15 ~15 GeV GeV for for m mρ

ρT T ≤

≤200 200 GeV GeV.

4 2 2 4

( ~ c o s ) ( ~ s in c o s ) ( ~ s in )

T T T T T L T L L

W W W ρ π π χ π χ χ χ → Π Π → → →

.

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Decays of Decays of π πT

T

• The

The technipions technipions π πT

T± ± π

πT

T0 0 decays, are induced mainly by

decays, are induced mainly by ETC interactions which couples them to fermions ETC interactions which couples them to fermions

• The

The π πT

T preferentially decay into the

preferentially decay into the heaviest heaviest fermion fermion pairs allowed pairs allowed, main modes being: , main modes being:

• Total width

Total width < 1 < 1 GeV GeV for for M Mπ

π ~ 100

~ 100 GeV GeV. .

( 90% ), ( 5% ), ( 5% ) ( 90% ), ( 5% ), ( 5% )

T T

bc sc v bb cc

τ

π τ π ττ

− →

≈ ≈ ≈ → ≈ ≈ ≈

'

2

; ( ) ( )

T i i T i i f f

f f f f m m π π

− −

→ Γ → ∝ +

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Technicolor at LEP Technicolor at LEP

• Although

Although TC model TC model is rather complicated, the is rather complicated, the phenomenology of the lightest bound states which it phenomenology of the lightest bound states which it predicts is relatively simple predicts is relatively simple with few free with few free parameters: parameters:

• M

Mπ πT

T mass of

mass of π πT

T

• M

Mρ ρT

T mass of

mass of ρ ρT

T

• sin

sin2

2χ

χ=1/N =1/ND

D number of doublets , or

number of doublets , or mixing angle of mixing angle of π πT

T and W

and WL

L

• For

For ω ωT

T production and decay, a scale parameter and

production and decay, a scale parameter and Q QU

U+Q

+QD

D must be specified. By analogy with QCD it is

must be specified. By analogy with QCD it is supposed that supposed that M Mρ ρT

T ~

~ M Mω ωT

T, and

, and M Mπ πT

T0 0 ~

~ M Mπ πT

T+ +.

.

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Technicolor production at LEP Technicolor production at LEP

• ρ

ρT

T couples with

couples with γ γ and Z and Z0

0 and can be produced at LEP in

and can be produced at LEP in s s-

• channel.

channel.

• If

If M Mρ ρT

T <

< √s, √s, ρ ρT

T can be

can be produced in RR process produced in RR process and can and can be observed as a be observed as a narrow resonance in s’ narrow resonance in s’ distribution. distribution.

• Technipions

Technipions can be produced through virtual can be produced through virtual ρ ρT

T

exchange in pairs or in association with W exchange in pairs or in association with WL

L:

:

• Production cross

Production cross-

• section of

section of TC objects was expected to TC objects was expected to be be reasonably high reasonably high, which allowed search at LEP. , which allowed search at LEP.

* * T T T T T L

e e e e W ρ π π ρ π

+ − + −

→ → → →

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Expected cross Expected cross-

• section

section

10

• 2

10

• 1

1 10 150 200 250 300

e+e- → ρTγ e+e- → ρT

* → πT + πT

• e

+

e

• →

ρ

T *

, ω

T *

→ π

T

γ

M(ρT) [GeV/c2] Cross-section [pb]

√s = 200 GeV

M Mπ

πT T=90

=90 GeV GeV N ND

D=9

=9 M MV

V=200

=200 GeV GeV (Q (QU

U+Q

+QD

D)=4/3

)=4/3 α αρ

ρ=2.91(3/N

=2.91(3/NTC

TC)

) (TC coupling (TC coupling constant) constant) N NTC

TC=4

=4

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*

,

L T T T T

e W e π π π ρ

+ − →

→

• This process is searched for in

This process is searched for in 4 jet 4 jet and in and in 2 jet+ 2 jet+ lepton+neutrino lepton+neutrino final final states. states.

• In both cases, a Neural Network is used which

In both cases, a Neural Network is used which combines combines topological variables topological variables and and b b-

• tagging

tagging

• The

The most important background for most important background for π

πT

T search is

search is e e+

+e

e-

• →

→W W+

+W

W-

• . The main difference between

. The main difference between W W+

+W

W-

• and

and π π+

+π

π-

• production is the presence of

production is the presence of b b-

• quark

quark in the in the decays of decays of π

πT

T.

. b b-

• tagging is essential.

tagging is essential.

• The mass is estimated after a

The mass is estimated after a 5c 5c constrained fit constrained fit imposing energy and momentum conservation and imposing energy and momentum conservation and equal masses equal masses of the two

• f the two fermion

fermion objects (

• bjects (qq

qq or

• r l

lυ υ). ).

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Discriminating Variables Discriminating Variables

Number of events per bin 1 10 10 2 10 3 5 10 MC qq

–(γ)

4-fermion DELPHI 10

• 1

1 10 5 10 b-tagging variable of the dijet with highest content in b-quarks 200 400 0.25 0.5 0.75 1 10 20 0.25 0.5 0.75 1 sum of the second and fourth Fox-Wolfram moments 200 400 600 20 40 60 80 5 10 15 20 20 40 60 80 product of the minimum jet energy and the minimum opening angle betweenany two jets 200 400 20 40 60 80 5 10 15 20 20 40 60 80 minimum di-jet mass

• NNW

NNW (4j channel) (4j channel) : :

• 2

2 b b-

• tagging variables.

tagging variables.

• 7 topological

7 topological ( (antiQCD antiQCD, , almost same as almost same as higgs higgs 4j) 4j)

• 3 based on

3 based on boson boson production properties. production properties.

• Semileptonic

Semileptonic channel channel: :

• isolated lepton

isolated lepton (3 NN) (3 NN)

• b

b-

• tagging

tagging (jet) (jet)

• boson production angle

boson production angle

T T L T

qq W l qq π π τν π ν

+ − + −

→ →

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Mass distribution in the 4jet channel Mass distribution in the 4jet channel

5 10 15 20 25 30 35 40 60 80 100 120 0 5 10 15 20 25 30 35 40 60 80 100 120

Number of events per bin Mass after 5c fit with equal masses (GeV/c2)

MC qq

–(γ)

4-fermion DELPHI πTπT W πT

Expected Expected technicolor technicolor signal for signal for M Mπ

πT T=100

=100 GeV GeV N ND

D=9

=9 M Mρ

ρT T=220

=220 GeV GeV

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Mass distribution in the Mass distribution in the semileptonic semileptonic channel channel

Expected Expected technicolor technicolor signal for signal for M Mπ

πT T=100

=100 GeV GeV N ND

D=9

=9 M Mρ

ρT T=220

=220 GeV GeV

2 4 6 8 10 12 14 16 18 20 25 50 75 100 2 4 6 8 10 12 14 16 18 20 25 50 75 100 Number of events per bin Mass (GeV/c2)

MC qq

–(γ)

4-fermion DELPHI πTπT → τν

– τ qq –

WπT → lν

– qq –

Small decay rate Small decay rate π π → →τυ τυ

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Background Background supresion supresion

Good agreement Good agreement between between data data and and SM SM prediction

qq

–(γ)

WW ZZ

Efficiency for πTπT with MπT=90 GeV/c2 Number of events

DELPHI √s = 192-202 GeV

1 10 10 2 10 3 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1 10 10 2 10 3 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

qq

–(γ)

WW ZZ

Efficiency for πTπT with MπT=99 GeV/c2 Number of events

DELPHI √s = 204-208 GeV

prediction Results used to Results used to set limits set limits on

• n Technicolor production

Technicolor production

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Limits on Technicolor Limits on Technicolor

Limit based on Limit based on CL CLs

s,

, using NN and mass. using NN and mass. Lower limit on Lower limit on M Mπ

πT T for

for M Mρ

ρT T →

→∞ ∞, , point like

point like coupling between gauge coupling between gauge bosons and bosons and π

πT

Tπ

πT

T

M Mπ

πT T>79.8 GeV/c

>79.8 GeV/c2

2

(95% CL) (95% CL) (81.1 GeV (81.1 GeV/

/c

c2

2

expected) expected)

DELPHI

60 80 100 120 100 200 300 400 e+e-→πTπT;πTWL e+e-→ρT(γ) : ρT→hadrons ρT→W+

LW- L

ND=2

M(ρT) [GeV/c2] M(πT) [GeV/c2]

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Limits on Technicolor Limits on Technicolor

DELPHI

60 80 100 120 100 200 300 400 e+e-→πTπT;πTWL e+e-→ρT(γ) : ρT→hadrons ρT→W+

LW- L

ND=9

M(ρT) [GeV/c2] M(πT) [GeV/c2]

Lower limit on Lower limit on M Mπ

πT T for

for M Mρ

ρT T →

→∞ ∞, , point like point like coupling coupling

M Mπ

πT T>89.1 GeV/c

>89.1 GeV/c2

2

(95% CL) (95% CL) (88.1 GeV/c (88.1 GeV/c2

2

expected) expected)

ρ ρT

T production

production excluded excluded 90< 90<M Mρ ρT

T<206.7

<206.7 GeV/c GeV/c2

2

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OPAL results OPAL results

[GeV]

5C

m

40 50 60 70 80 90 100

events / 2 GeV

2 4 6 8 10 12 14 16

2-fermion 4-fermion =0.5 pb ) σ signal ( OPAL data

[GeV]

5C

m

40 50 60 70 80 90 100

events / 2 GeV

2 4 6 8 10 12 14 16 OPAL Preliminary

60 80 100 120 140 250 300 350 400 450 500 550 600

excluded OPAL Preliminary mρ/ω [GeV] mπ [GeV]

π T

0γ→bb –γ MV=200GeV

π T

0γ→bb –γ MV=100GeV

π T

+ π T

• → bq

–b –q,

Based on ~ Based on ~ 209.4 pb 209.4 pb-

• 1

1 up to up to 209 209 GeV GeV. . No excess was observed No excess was observed

Lower limit on Lower limit on M Mπ

πT T for

for M Mρ

ρT T →

→∞ ∞, ,

M Mπ

πT T>62 GeV/c

>62 GeV/c2

2 (

(N Nd

d=2)

=2)

M Mπ

πT T>77 GeV/c

>77 GeV/c2

2 (

(N Nd

d=9)

=9) (95% CL) (95% CL)

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Search for Search for ρ ρT

T with

with M Mρ

ρT T<

<√ √s s

• ρ

ρT

T with

with M Mρ

ρT T<√s can be produced on mass shell in RR

<√s can be produced on mass shell in RR process process e e+

+e

e-

• →

→ρ ρT

T(

(γ γ) ) with subsequent decays into with subsequent decays into different final states. different final states.

• It can be observed as relatively narrow resonance in

It can be observed as relatively narrow resonance in the corresponding mass distribution the corresponding mass distribution Γ Γρ

ρT T≤

≤15 15 GeV GeV for for m mρ

ρT T ≤200

≤200 GeV GeV

• It also gives additional contribution in the production

It also gives additional contribution in the production cross cross-

• sections of SM final states, e.g.

sections of SM final states, e.g. e e+

+e

e-

• →

→ρ ρT

T* *→

→ W W+

+W

W-

• ρ

ρT

T is searched for in all main decay modes:

is searched for in all main decay modes:

ρ ρT

T →

→ hadrons ( hadrons (π πT

Tπ

πT

T,qq

,qq), ), π πT

T 0γ

γ, , W WL

L + +W

WL

L

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Direct Search for Direct Search for ρ

ρT

T →

→ π πT

T0 0γ

γ

• Narrow resonance should be

Narrow resonance should be

• bserved in the mass
• bserved in the mass

spectra of: spectra of:

• Again the use of

Again the use of b b-

• tagging

tagging is important, since the main is important, since the main π πT

T0 0 decay is into b

decay is into b-

• quarks.

quarks.

• Result obtained:

Result obtained:

BR( BR(ρ ρT

T →

→ π πT

T 0γ

γ)<7%, )<7%, (95%CL) (95%CL)

5 10 15 20 100 125 150 175 200 M(qq

–γ) [GeV/c2]

Events/5 GeV/c2

a

1 10 10 2 50 100 150 200 M(qq

–) [GeV/c2]

Events/5 GeV/c2

b

T T

qqγ from qq ρ π →

M Mρ ρT

T>√s

>√s

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Indirect search for Indirect search for ρ ρT

T →

→ W W+

+W

W-

• In the presence of

In the presence of ρ ρT

T →

→ W W+

+W

W-

• , measured cross section

, measured cross section e e+

+e

e-

• →

→W W+

+W

W-

• should

should differ significantly differ significantly from the from the SM prediction SM prediction. . Predicted additional contribution are quite large: Predicted additional contribution are quite large:

• These values can be compared with experimental precision, e.g.

These values can be compared with experimental precision, e.g. Delphi at Delphi at √s √s =189 =189 GeV GeV gives gives σ σ(e (e+

+e

e-

• →

→ W W+

+W

W-

• ) =15.83

) =15.83±0.38±0.20 ±0.38±0.20 pb pb and the expected SM value is and the expected SM value is ~16.25 ~16.25 pb pb

• As no additional contribution is observed in the cross

As no additional contribution is observed in the cross-

• section,

section,

BR( BR(ρ ρT

T →

→ W W+

+W

W-

• )<30%, (95%CL)

)<30%, (95%CL)

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Indirect Search for Indirect Search for ρ ρT

T →

→ hadrons ( hadrons (π πT

Tπ

πT

T,qq

,qq) )

• ρ

ρT

T should also give an

should also give an additional contribution to additional contribution to the process the process

• It should be observed as a

It should be observed as a peak in the peak in the hadronic hadronic mass mass distribution. distribution.

• BR(

BR(ρ ρT

T→

→hadrons hadrons)<55%, )<55%, (95%CL) (95%CL)

( )

e

e qq γ

+ − →

DELPHI

500 1000 1500 2000 2500 3000 3500 80 100 120 140 160

a

M(hadrons) [GeV/c2] Events

• 80
• 60
• 40
• 20

20 40 60 80 100 120 80 100 120 140 160

b

M(hadrons) [GeV/c2] NObs-NSM 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 80 90 100 110 120 130 140 150 160 M(ρT) [GeV/c2] Br(ρT→hadrons)

95% CL Upper limit

c

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LEP vs. LEP vs. Tevatron Tevatron

• Results at

Results at Tevatron Tevatron using the using the same TC model are based on same TC model are based on l+2j l+2j channel (counting channel (counting experiment, in mass experiment, in mass windows). windows).

• No

No excess was observed excess was observed, , then, data is used to exclude then, data is used to exclude mass regions in the mass regions in the M Mρ

ρT T vs.

vs. M Mπ

πT T plane.

plane.

• Using

Using INDIRECT INDIRECT searches searches at at LEP LEP this plane is almost this plane is almost completely completely covered covered. .

80 85 90 95 100 105 110 115 160 165 170 175 180 185 190 195 200 205

15pb 10pb 5pb

95 % C.L. Excluded Region

MRSG p.d.f. multiplied by Kfactor=1.3 Technicolor model by E.Eichten and K.Lane

• Phys. Lett. B388:803-807, 1996

ρT

± → W± + πT 0 and

ρT

0 → W± + πT ± processes

( πT

0 → bb – , πT ± → bc –, cb –)

CDF 109 pb-1

ρT→WπT kinematical threshold

ρT mass [GeV/c2] πT mass [GeV/c2]

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Excited leptons (Compositeness) Excited leptons (Compositeness)

• Substructure at an energy scale

Substructure at an energy scale Λ Λ →

→ Excited leptons

Excited leptons

– – Decay promptly: Decay promptly:

• l*

l* → → l lγ γ, ,υ υW,lZ W,lZ

• υ

υ* * → → υγ υγ υγ υγ,lW, ,lW,υ υZ Z

– – f/ f/Λ Λ, f , f’ ’/ /Λ Λ vs. m

• vs. ml*

l* (|f|=|f

(|f|=|f’ ’|) |)

• Direct searches were performed in

Direct searches were performed in pairs pairs ( (~√s/2 ~√s/2), ), and in and in single single production ( production (~√s ~√s). ).

• Indirect searches for excited electrons, using the

Indirect searches for excited electrons, using the measured measured γγ γγ γγ γγ( (γ γ) ) differential cross differential cross-

• section.

section.

• Opal and Delphi results already combined, Aleph and

Opal and Delphi results already combined, Aleph and L3, similar sensitivities. L3, similar sensitivities.

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Excited leptons (direct searches) Excited leptons (direct searches)

• No excess of events

No excess of events was observed with respect the Standard was observed with respect the Standard Model prediction: Model prediction:

• Exclusion for

Exclusion for f/ f/Λ Λ vs. M

• vs. Ml*

l* at

at √ √s s =189 =189-

• 210

210 GeV GeV

10

• 2

10

• 1

1 10 10 2 100 120 140 160 180 200

Ml* [GeV/c2] f/Λ [TeV

• 1]

DELPHI&OPAL preliminary f = f’

e* µ* τ* e x c l u d e d

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Excited leptons (indirect searches) Excited leptons (indirect searches)

• No excess of events

No excess of events was observed with respect the Standard was observed with respect the Standard Model expectation: Model expectation:

• Exclusion for

Exclusion for f/ f/Λ Λ vs. M

• vs. Ml*

l* at

at √ √s s =189 =189-

• 210

210 GeV GeV

10

• 2

10

• 1

1 10 10 2 100 120 140 160 180 200 220 240 260 280 300

Me* [GeV/c2] f/Λ [TeV

• 1]

DELPHI&OPAL preliminary e*, f = f’

ZEUS preliminary H1

excluded

D&O

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Summary Summary

• LEP

LEP provided data samples to look for new physics beyond the provided data samples to look for new physics beyond the Standard Model, allowing investigation of new phenomena and sear Standard Model, allowing investigation of new phenomena and search ch for new particles. for new particles.

• Results obtained, either

Results obtained, either combined combined among the four LEP experiments or among the four LEP experiments or coming from coming from individual individual experiments experiments gives NO evidence gives NO evidence of the

• f the

presence of new physics, presence of new physics,

– – No evidence of Technicolor contribution No evidence of Technicolor contribution is observed is observed – – A 95% CL A 95% CL lower mass limit of

lower mass limit of 79.8 GeV/c 79.8 GeV/c2

2 is set

is set independently independently of other

• f other

parameters of the TC model. parameters of the TC model.

– – 90< 90<M Mρ ρT

T<206.7

<206.7 GeV/c GeV/c2

2 is set regardless other model parameters

is set regardless other model parameters.

.

– – f/ f/Λ Λ Λ Λ ≤ ≤ 0.1 TeV 0.1 TeV-

• 1

1 (e*), 1 TeV

(e*), 1 TeV-

• 1

1 (

(µ µ*, *,τ τ*) *)

• Final LEP combined results

Final LEP combined results, coming soon from LEP , coming soon from LEP EXOTICA WG. EXOTICA WG.