Searches at LEP

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Searches at LEP
Moriond Electroweak 2004
Ivo van Vulpen CERN
On behalf of the LEP collaborations
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LEP and the LEP data
? LEP ee- collider at ?s ? mZ (LEP1) and ?s
130-209 GeV (LEP2)
Most results (95 CL limits) based on LEP2
Int. Lum. ? 2.6 fb-1
4 experiments Aleph, Delphi, Opal and L3
Outline of the talk
e otica
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Higgs Searches
Higgs Searches
http//lephiggs.web.cern.ch/LEPHIGGS/www/Welcome.h
tml
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Higgs Searches
Higgs Searches covered in this talk
? SM Higgs boson
? General 2HDM
?MSSM (CP-conserving)
? 3 benchmarks
? Flavour independent
? Charged Higgs boson
? MSSM (CP non-conserving)
? Fermiophobic
? Invisible Higgs boson
? Not covered MSSM Gluophobic (LHC), Double
charged Higgs bosons, Anomalous Higgs couplings,
Yukawa Higgs production, Extended Models, many
many more
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Higgs Searches
SM Higgs boson
Higgs strahlung
h
In the SM we know everything about the Higgs boson
(except its mass)
mh 115.3 GeV (expected)
?
mh 114.4 GeV (observed)
Weak boson fusion
Excess at 115 GeV -2ln(Q) at mh 115 GeV
Exclusion on HZZ coupling
100,000 signalbackground experiments (MC)
100,000 background-only experiments (MC)
LEP data
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Higgs Searches
Two Higgs Doublet Models (2HDM)
? Simplest extension of the SM Add 2 complex
Higgs Doublets (H1, H2)
Parameters tan(?) (v1/v2) , ? (mixing h0,H0)
Higgs boson masses
Higgses 2 CP-even h0, H0
Models 2HDM(I) One doublet for all fermions
1 CP-odd A0
2HDM(II) One up-type doublet
MSSM
2 charged H,H-
One down-type doublet
Neutral Higgs boson production
Higgs boson decay
Depends on model parameters
couples to mass, so mainly
Higgs strahlung
Associated production
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Higgs Searches
Higgs Searches
MSSM
7 parameters
Tree-level parameters
?tan(?) Higgs vev ratio
?mA Mass of CP-odd Higgs
Three benchmark scenarios
1) mh-max (max mh for each tan(?) )
Loop-level parameters
2) no-mixing (in the stop sector)
?A Trilinear Higgs-sfermion coupling
?mg Mass of the gluino
?? Higgs mass parameter
?msusy Sfermion mass at EW scale
?M2 Gaugino mass at EW scale
Xt stop mixing At - ? cot(?)
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Higgs Searches
Higgs Searches
MSSM benchmark (large ?)
? Lightest Higgs mh Higgs decays to cc or gluons
LEP combined 88-209 GeV
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Higgs Searches
Higgs Searches
MSSM benchmarks
Mh-max
No-mixing
?hZ small
?hA kinem. out of reach
Mh2mA h-AA dominant
Extend searches for h-AA (mAconservative tan(?) exclusion depends strongly on
the top mass
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? Influence of the top mass on tan(?) exclusion
region
In MSSM benchmarks mtop 175 GeV
Maximum mh in the MSSM ? 135 GeV

?Computation of mh-max
Loop corrections ? m4top
FeynHiggs
higher order corr. - ?mh ? 3 GeV
mh-max benchmark scenario
?mtop ? 5 GeV - ?mh ? 5 GeV
mh
? If mtop is larger than 175 GeV, the
LEP-excluded tan(?) region shrinks
Depends on results from CDF D0 -- K. Bloom
Y.Kulik (this session)
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Higgs Searches
Higgs Searches
MSSM
CP non-conserving scenarios
? Break CP symmetry by radiative corrections
Low mass regions open up
tan(?) versus mH1
CP conserved (H1, H2) - mass eigenstates are
CP-eigenstates
h,H (CP-even), A (CP-odd)
ee- - hZ and ee- - hA
CP H1, H2 H3 are mass-, but not CP-eigenstates
A
tan(?)
M2 ? m4top Im (?,At) / v2 m2susy
OPAL
CP benchmark CPX Scan parameters tan(?) and
mH
mH1
(Msusy 500 GeV, ?4 Msusy, At,bmg2 Msusy )
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Higgs Searches
Fermiophobic Higgs bosons
? In 2HDM (I) models Higgs couplings to fermions
can be close to 0
? Decays to photons (W-loop) is dominant
mh 109.7 GeV (observed)
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Higgs Searches
Invisible Higgs bosons
? MSSM Higgs boson might decay into
Expected Cross section
LEP combined
stable
Excluded Cross section
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Higgs boson summary
Observed Lower limit on mh (GeV)
Higgs scenario
SM Higgs 114.4 GeV
Flavour independent 112.9 GeV
Charged Higgs bosons 78.6 GeV
Fermiophobic 109.7 GeV
Invisible 114.4 GeV
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SuperSymmetry
http//lepsusy.web.cern.ch/lepsusy/
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SUSY Searches
SUSY model covered in this talk
? R-parity conservation
there is a stable Lightest Supersymmetric
Particle (LSP)
SUSY particles are produced in pairs
? Mass universality at the GUT scale
sfermions (m0)
cMSSM
gauginos (m1/2)
8 parameters m1/2, m0, tan(?), ?, mA and
Af(At, Ab, A?)
? SUSY broken by gravitation (SUGRA)
Signature Missing energy (escaping
neutralino) and dependence on ?M (msparticle-
mLSP)
This talk Results on sleptons, squarks,
charginos -- lower limit on the mass of the LSP
Last slide Results on R-parity violation, GMSB.
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SUSY Searches
sleptons
? production
?M small
e
cross sections for lR smaller than lL
? decay
?M
? -200 GeV and tan(?) 1.5
very soft leptons
? Mass limits

Lower limits in GeV
0 GeV 99.6 94.9 85.9
85.0
from the Z

40 GeV 99.4 96.5 92.5
91.7
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SUSY Searches
? production
? (main) decays
squarks
stop
?Mixing in 3rd family
? Mass limits (in GeV)
?M 20 GeV for (non)-decoupled from Z
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SUSY Searches
new
A light sbottom
Excess in bb cross section at the Tevatron
How about a 12-16 GeV gluino and 2-5.5 GeV
sbottom ??
P.Janot hep-ph/0403157
? Moriond 2003 (ALEPH)
Stable sbottoms Msbottom 92 GeV

? Hadronic cross section data from
95 CL lower limit on msbottom (GeV)
LEP1, LEP2 and PEP, PETRA, TRISTAN,
Small coupling sbottom to Z
The older generations in the LEP family help out
(use ?s 20-209 GeV)
Hadronically decaying sbottom Msbottom 6.0
GeV
cos ?mix
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Small m0 light sfermions
Charginos large m0
Large cross section in large part of parameter
space
? production
? decay
Negative interference if chargino is gaugino
W- qq (68) / lv (32)
1) ?M 3 GeV
LEP combined
2) 200 MeV low momentum particles (use ISR - high PT-?)
3) ?M kinky tracks and displaced vertices
Long lived charged particles (dE/dx information)
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SUSY Searches
The LSP
cMSSM
? Interpret the combined results in the cMSSM
framework
Combining results from Higgs searches with
slepton, chargino and neutralino searches
Use cMSSM mass relations
m0 large
m0 small
Assuming m0 stau mixing
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SUSY Searches
The LSP
mSUGRA
? Interpret the combined results in the mSUGRA
framework
MSUGRA cMSSM 1) common scalar mass
(mA via m0)
2) common trilinear coupling at GUT (At,
Ab, A? A)
3) fix ? (EW symmetry breaking) (? -
sign(?))
5 parameters m1/2, m0, tan(?), sign(?), A
A0, mtop 175 GeV
A0, mtop 180 GeV
Any A mtop 175 GeV
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SUSY summary
? Not shown AMSB scenarios where the
sneutrino or the gluino is the LSP
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Exotica Searches
Low scale gravity in
Extra dimensions
? Gravity strong near the EW scale
Data/MC
n extra (space) dimensions of radius r
? Virtual graviton exchange affects
? Put limits on MH (gravitational mass scale)
MH 1.20 TeV (? 1)
cos(?e)
MH 1.09 TeV (? -1)
? Not shown technicolour, single top,
leptoquarks, excited fermions, Z, cont.
interactions,
4th generation quarks
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Conclusions
? SM Higgs combined and published
Searches for SUSY Higgs bosons - exclude large
part of MSSM parameter space
Final benchmark scans this summer (also
gluophobic interesting for LHC)
? LEP combined searches for sparticles
Interpretations in a wide variety of SUSY models
Rest of the cheese is for the Tevatron LHC
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Backup slides
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Higgs Searches
Hypotheses testing Likelihood ratio method
? Construct 2-dim distr. for background(mh) and
signal(mh)background -- (Mhrec, ?)
Higgs mass estimator
? For each event i - you know wi P(sb)/P(b)
separating variable
? Define test-statistic as 2ln(Q), with Q
Lsb / Lb (?i wi)
with weights
Number of expected signal events
Ratio of the expected number of signal events
over the expected number of signal events in a
locql bin of (Mhrec, ?)
Number of selected candidates
100,000 signalbackground experiments (MC)
100,000 background-only experiments (MC)
The rules
LEP
1-Clb incompatibility with the background-only
hypothesis
1-Clb 3 sigma
1-Clb Nobel Prize !
CLsb compatibility with the signalbackground
hypothesis
1-Clb
Clsb
CLs compatibility with a signal hypothesis. CLs
? CLsb/CLb
Cls Signal hypoth. excluded
at 95 CL
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Higgs Searches
Charged Higgs bosons
? Assumption of fermion decay is not valid in
unexcluded 2HDM(II) no-mixing point
Br(H- AW) can be 60
?mA special effort
Extended h-AA reach (A-cc/??-/gluons)
BR(H-- ???)
WW background
OPAL
Excluded
Excluded LEP1
Excluded
But unfortunately
Included in next (final?) benchmark scan
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SUSY Searches
Neutralinos

• neutralino decay

? neutralino production
Z- qq (70) / v v (20) / ll(10)
Positive interference if neutralino is gaugino
? Phenomenology depends on ?M, but also on m0
(common sfermion mass at GUT scale)
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Exotica
? Excited leptons
Fermion sub-structure
(compositness scale in TeV region)
Excluded
Decay l - l? / lZ / W?
?
?
More sensitive due to t-channel ?- exchange
e
? Not covered technicolor, single top,
leptoquarks, extra dimensions, etc