Search for Excited Fermions

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Search for Excited Fermions
Bernardo Tomé LIP/Lisboa (On behalf of the DELPHI
and H1 collaborations)
EPS HEP 2005, Lisboa
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OUTLOOK
Introduction Experimental signatures
Results from DELPHI (LEP) H1 (HERA)
(abstracts 91 639) Conclusions
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Compositeness Models
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A phenomenological model
Boudjema, Djouadi, Kneur Z.Phys.C57
(1993) Hagiwara, Zeppenfeld, Komamiya Z.Phys.C29
(1985)
Excited fermions have spin½ and weak
isospin½ Both L-handed and R-handed components
form weak isodoublets
Effective Lagrangean
SU(2) x U(1) x SU(3) symmetry
ff V coupling f deexcitation to a SM fermion
and a gauge boson ( Vg, Z, W, g).
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Excited fermion production
LEP (e e-)
Pair
Single
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Excited fermion decays
Usual assumptions f f or f - f
l and n searches
f f n -gt n g forbidden
f - f l -gt l g forbidden
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Results for EPS HEP 2005
DELPHI (LEP)
Abstract 91 - Search for excited leptons in
ee- collisions at c.m.e 189-209 GeV.


Charged and neutral excited leptons from all 3
generations. Single and double production
searches. 600 pb-1 at c.m.e. 189-209 GeV.
H1 (HERA)
Abstract 639 - Search for excited fermions at
HERA.
q search 37 pb-1 at c.m.e. 300 GeV (e p)
ne search 15 pb-1 at c.m.e. 318 GeV (e-
p) New results in progress...
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DELPHI final states investigated
g, (l)lg, llg,jj, jj(l), jjl, jjll
Single
g g, ll g g, jjjj, jjl, jjjjll, jjlll
Pair
Topologies with jets, isolated photons, isolated
leptons.
Sequential (cuts based) analyses. Discriminant
analysis for jjl, jjjj in pair production search.
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DELPHI analyses
Single production search
Pair production search
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DELPHI results
Agreement between data and SM expectations.
Pair production search Excluded excited
lepton masses 100 GeV.
Single production search Upper limits on f/L
vs ml
Charged
Neutral
EXCLUDED
EXCLUDED
Results also for f -f
All limits at 95 C.L.
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DELPHI results (cont.)
e indirect search in
Deviations from QED were searched for.
EXCLUDED
Indirect
Direct
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H1 q search
q -gt q g, q W, q Z
q decays
Final states
1 photon 1 jet 3 high ET jets
Final states from W Z decays into electrons or
muons
W, Z hadronic decays
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H1 results (q and n searches)
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Concluding

• No hint of excited fermion production in ee- or
  ep collisions.

• Excited lepton masses excluded up to 100 GeV.

• Upper limits on the ratio f /L derived up to
  300 GeV.

• Waiting for surprises from the LHC.

• but... sub-PeV ( 102 TeV ) domain could be
  accessible in collisions of Cosmic Rays with the
  atmosphere !

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THE END
THE END ?
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