LEP Search for Single Top production and new fermions

LEP Search for Single Top LEP Search for Single Top production and new fermions production and new fermions

Mario Antonelli

LNF-INFN Frascati

ICHEP 2002 Amsterdam

on behalf of the 4- LEP experiments

All limits are at 95 % CL and preliminary

The LEP e+e- collider

88-95 `89-`95 ~175130,136 `95,`9 ~10161,172 `96 ~10, ~10181-184 `97 ~55189 `98 ~170192,196,200,202 `99 ~(30,80,80,30)205 – 208 `00 ~207 >208 ‘00 ~3

/exp)(pbLdt -1 ECM (GeV) Year

High centre of mass energy + Luminosity + clean experimental environment

Search for single top production via FCNC )u ,cq( qtee

At tree level SM, there are no vertices for these FCNC processes (GIM mechanism VCKM=VCKM

-1).

FCNC appear at loop level

Very small cross section ( 10-9

fb)

Suppressed by loop + GIM

Extensions of SM could lead to enhancement of such transitions

The FCNC vertices tqV (V = ,Z) probed in

Existing limits

HERA: Xteuep

0.19)(K 0.7% )uBR(t tu

Sensitivity to tucouplingKut

ZEUS:

SM: -1310 5.2 1.5, cZ) ,cBR(t

TEVATRON: Xttpp

33% uZ)BR(tcZ)BR(t

3.2% )uBR(t)cBR(t

CDF:

• rare decays of top quark• top-q associated production

very weak constraint: Ntt~102

Using the following vertices

νμν

t

qγ

γμ qσ

m

eeKΓ μ

WZ

Zμ γ

sin2θ

eKΓ

CDF upper limits on BR translate

0.176K2γ

0.533K2Z

corresponding to CDF limits

CDF(200,174) < 0.85 pb

174

179

169

Top decays rapidly via (10-24 sec) no top hadrons formed

ff

bW

tcee

c-jetb-jet

Topologies

Et ~ mt

EW ~ (mt2+mW

2-mb2)/2mt

Eb ~ (mt2-mW

2+mb2)/2mt

Eq ~ s - mt

Kinematics at 189 GeV

c-jetb-jet

W-jet

W-jet

Selections and performances 2 selections: and W decay hadronic Leptonic

kinematics + b-tag + lepton id + Emiss

OPAL

~

Bkg ~

10%-15% 4%-7%

No excess seen in data

50-200 fb (WW,qq) 10-30 fb (WW)

Combined* LEP results

*LR method for combination

LEPEXOTICA WG

Cross section upper limits for mt =174 GeV <s>

GeV95(obs)

pb

95(exp)

pb

189 0.11 0.11

192 0.38 0.33

196 0.36 0.20

200 0.21 0.21

202 0.30 0.35

205 0.20 0.25

207 0.17 0.18

Limits on FCNC couplings

ADLO

About 0.55 fb-1 per experiment

Combined* LEP results

*LR method for combination

LEPEXOTICA WG

Cross section upper limits for mt =174 GeV <s>

GeV95(obs)

pb

95(exp)

pb

189 0.11 0.11

192 0.38 0.33

196 0.36 0.20

200 0.21 0.21

202 0.30 0.35

205 0.20 0.25

207 0.17 0.18

Limits on branching ratios

About 0.55 fb-1 per experiment

ADLO

and beyond

New fundamental particles ?

Substructures?

Fermions in SM

Sequential, vector, mirror

L 0LIsosinglet neutrino

lN

ub

c

dt

sL LL

eeν μν τν

μ τL LL

Re

Rμ Rτ

Ru Rd RsRcRt Rb

Search for excited and heavy fermions

Excited Leptons *l *

lν

Heavy quarks b'

Vector L

Sequential

L

Search for heavy fermions

γZ

e

e F

F

_Production:eNe

eW

Decay*:

*decay to W favored these energies

L 0L

W

l0 N,L,L l,ν l

WU

b' b

Z

NEW

Wt'tb' M)(MMM Could be sizeable if :

Ue

eν

Heavy leptonsJets and leptons

lWL 0 eWNe

...,,),(,_

ZZffWW*

Bkg* ~ 0.3-1 pb

Emiss + Ptmiss

νWL

~ 35-

15%

J-L

Candidates in agreement with SM expectation

0LLMM depending on

WLL 0

(5%)

Heavy stable charged particles

0LLMM Small U

and

HSCP

65%

0.01 pbdecay length: U-2ML

-6

Decay Mode Model Dirac Majorana

Sequential

Vector

Mirror

101.3

102.6

100.8

89.5

-----

89.5

Sequential

VectorMirror

101.5

102.7

101.0

90.7

-----

90.7

Sequential

Vector

Mirror

90.3

99.3

90.3

80.5

-----

80.5

WeL0

WμL0

WτL0

Lower mass limits

Decay Mode

100.8

101.2

100.5

101.9

102.1

101.9

Stable

102.6

102.6

102.6

WνL

WLL 0

WLL 0 limits

eWNe

72

l 10U 352

l 1010U MN < 3 GeV3 < MN < 80 GeV

Search for ZZbb'bb'ee__

llbb qqbbbjets

bjets

NEW

+ clean signature - BR (ZZ->llvv) ~4%

- large background + BR (ZZ->qqvv) ~28%

simple cut analysis shape analysis

Search for NEW

efficiency ~50% (x 4%) ~40% (x 28%) for Mb’=100 GeV background ~ 8 ~665 data 8 599 95(exp) 0.8 pb 0.29 pb 95 0.65 pb 0.26 pb

Preliminary results about 344 pb-1 at energies above 200 GeV

Combined: <0.21 pb for Mb’=100 GeV

95= 95% CL upper limit on 2_

bZ))BR(b''bb'eσ(e

CDF limits (PRL 84 (2000) 835) Mb’=100 GeV : 37pbbZ))BR(b''bb'pσ(p 2

__

102pb)SM'bb'pσ(p__

0.6pb)SM'bb'eσ(e_

at s=206.6 GeV

ZZbb'b b'ee__

0.35bZ)BR(b' 2

360.bZ)BR(b' 2

DELPHI

CDF

2_

bZ))BR(b''bb'eσ(e

llbb qqbb

Search for excited leptons

)ee no -f'fno f'f :(eg * γ γνν e*e

f, f’ control strength of SU(2), U(1) couplings

_

γZ

e

e *

*

single production

Substructure at a scale excited leptons

*lν lν

ZW,γ,/ΛfV

Prompt decay:

Pair productionγZ

e

e *

/ΛfV

e

eWZ,γ,

e*,e*/ΛfV

Virtual contribution

e

e

/ΛfV

WZ,γ,

WZ,γ,

e*,e*

/ΛfV

*

e,e

Photons, Leptons and photons

Search for pair produced excited leptons

Mass reach up to s/2

Topologies: as heavy leptons +

f = f ´ 103.0 103.1 102.2 102.0 102.4 95.3

f = -f ‘ 98.0 98.0 98.0

102.7 102.8 102.8

f = f ´ 102.9 102.9 102.8

*τν*

μv*τ*μ*e *eν

Single production Mass reach extended up to ~s

Many topologies:

radiative CC NC

Typical efficiency: 15% (W ) – 60%

()

(1/TeV) ΛfCombined LEP results LEPEXOTICA WG

*ee

e

γ

γe

du,

γ,Z

e*

du,

Conclusion

LEP is (was) beautifull: centre-of-mass energies and luminosities above the specifications.

We look forward to the near(?) future

New physics thoroughly searched for with the 2.5 fb-1 luminosity collected at LEP at Ecm up to 209 GeV

Numbers and properties of the events selected generally in agreement with SM expectation

Experimental constrains are dramatically improved.

WνL4 jets and missing energy

stableLAnomalous ionization loss

Combined LEP results

*ee

e

γ

γ