lep search for single top production and new fermions
DESCRIPTION
LEP Search for Single Top production and new fermions. Mario Antonelli LNF-INFN Frascati ICHEP 2002 Amsterdam. on behalf of the 4- LEP experiments. The LEP e + e - collider. E CM (GeV) Year. 88-95`89-`95 ~ 175 130,136 `95,`9 ~ 10 - PowerPoint PPT PresentationTRANSCRIPT
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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
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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
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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
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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
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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
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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)
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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
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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
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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'
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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
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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
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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
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WLL 0 limits
eWNe
72
l 10U 352
l 1010U MN < 3 GeV3 < MN < 80 GeV
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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
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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
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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
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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
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Single production Mass reach extended up to ~s
Many topologies:
radiative CC NC
Typical efficiency: 15% (W ) – 60%
()
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(1/TeV) ΛfCombined LEP results LEPEXOTICA WG
*ee
e
γ
γe
du,
γ,Z
e*
du,
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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.
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WνL4 jets and missing energy
stableLAnomalous ionization loss
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Combined LEP results
*ee
e
γ
γ