LEP Search for Single Top production and new fermions
description
Transcript of 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