1. Searches at LEP Ivo van Vulpen CERN
Moriond Electroweak 2004
Ivo van Vulpen
CERN
On behalf of the LEP collaborations

2. LEP and the LEP data Outline of the talk e otica iggs searches
 LEP: e+e- collider at s  mZ (LEP1) and s = 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
USY searches
iggs searches
e otica
Moriond EW 2004
Ivo van Vulpen

3. Higgs Searches http://lephiggs.web.cern.ch/LEPHIGGS/www/Welcome.html
Moriond EW 2004
Ivo van Vulpen

4. 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 ……
Moriond EW 2004
Ivo van Vulpen

5. SM Higgs boson  h In the SM we know everything about the Higgs boson
Higgs Searches
SM Higgs boson
Higgs strahlung h
In the SM we know everything about the Higgs boson
(except its mass)
mh > GeV (expected) 
mh > GeV (observed)
Weak boson fusion
Excess at 115 GeV: -2ln(Q) at mh = 115 GeV
100,000 signal+background experiments (MC)
Exclusion on HZZ coupling
100,000 background-only experiments (MC)
LEP data
Moriond EW 2004
Ivo van Vulpen

6. Two Higgs Doublet Models (2HDM)
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
2 charged: H+,H-
One down-type doublet
MSSM
Neutral Higgs boson production:
Higgs boson decay: h h A
Depends on model parameters
couples to mass, so mainly:
Higgs strahlung
Associated production
Moriond EW 2004
Ivo van Vulpen

7. Tree-level parameters
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
3) large- (H in reach, but regions with
reduced bb couplings)
mg Mass of the gluino
 Higgs mass parameter
msusy Sfermion mass at EW scale
M Gaugino mass at EW scale
Moriond EW 2004
Xt = stop mixing = At -  cot()
Ivo van Vulpen

8. MSSM benchmark (large )
Higgs Searches
Higgs Searches
MSSM benchmark (large )
Flavour independent Higgs bosons
Mass exclusion using SM(hZ):
mh > GeV (expected)
mh > GeV (observed)
2.3 GeV worse than SM Higgs
DELPHI hA -> hadrons (preliminary)
Model independent
mS1
mS2
100%
10%
 OPAL also made a decay mode independent search hZ hA
 Lightest Higgs: mh < 108 GeV
 Reduced couplings to bb
Higgs decays to cc or gluons
LEP combined: GeV
 Adding flavour independent
excludes large- scenario
unexcluded
Moriond EW 2004
Ivo van Vulpen

9. Mh-max MSSM benchmarks No-mixing
Higgs Searches
Higgs Searches
Mh-max
MSSM benchmarks
No-mixing
hZ small
hA kinem. out of reach hZ hA
Mh>2mA: h->AA dominant
Extend searches for h->AA (mA<mb) and H+
Scenario mh mA Excluded tan()
No mixing > > < tan() < 10.5
Mh-max > > < tan() < 2.4
conservative tan() exclusion depends strongly on the top mass
Moriond EW 2004
Ivo van Vulpen

10. mh ~  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 & D > K. Bloom & Y.Kulik (this session)
Moriond EW 2004
Ivo van Vulpen

11. CP non-conserving scenarios
Higgs Searches
Higgs Searches
MSSM
CP non-conserving scenarios
 Break CP symmetry by radiative corrections
Low mass regions open up
CP conserved: (H1, H2) -> mass eigenstates are CP-eigenstates
tan() versus mH1
h,H (CP-even), A (CP-odd)
e+e- -> hZ and e+e- -> hA
CP: H1, H2 H3 are mass-, but not CP-eigenstates
t,b
˜ ˜
h,H H1
Note: only h,H (CP-even) couple to Z. A
Different CP-phase A
tan()
M2  m4top Im (,At) / v2 m2susy
OPAL
CP benchmark: CPX Scan parameters: tan() and mH+
mH1
(Msusy = 500 GeV, =4 Msusy, |At,b|=|mg|=2 Msusy )
Moriond EW 2004
Ivo van Vulpen

12. Fermiophobic Higgs bosons
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  h Z
mh > GeV (observed)  WW
ZZ*
100 GeV
Roughly 100 times SM prediction
Moriond EW 2004
Ivo van Vulpen

13. Invisible Higgs bosons
Higgs Searches
Invisible Higgs bosons
 MSSM: Higgs boson might decay into
Expected Cross section h
LEP combined
stable
Excluded Cross section
Mh > GeV (exp.)
Mh > GeV (obs.)
Moriond EW 2004
Ivo van Vulpen

14. Higgs boson summary: Observed Lower limit on mh (GeV) Higgs scenario
SM Higgs GeV
MSSM (h) GeV
MSSM (A) GeV
Flavour independent GeV
Charged Higgs bosons GeV
Fermiophobic GeV
Invisible GeV
Moriond EW 2004
Ivo van Vulpen

15. SuperSymmetry http://lepsusy.web.cern.ch/lepsusy/ Moriond EW 2004
Ivo van Vulpen

16. SUSY model covered in this talk
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.
Moriond EW 2004
Ivo van Vulpen

17. sleptons e e e+ e- M  production M small
SUSY Searches
sleptons
 production
M small e e
Z/ e+ 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
from the Z
= 40 GeV
Moriond EW 2004
Ivo van Vulpen

18. squarks e+ e- sbottom  production:  (main) decays
SUSY Searches
 production:
 (main) decays
squarks
stop
sbottom
Z/ e+ e-
sbottom
stop
Mixing in 3rd family:
M< mc: squark is a quasi-stable particle
 Signature: acoplanar jets + E and P
 Mass limits (in GeV):
M = 20 GeV & for (non)-decoupled from Z
Mass limit (98) (96) (95)
Moriond EW 2004
Ivo van Vulpen

19. new A light sbottom cos mix
SUSY Searches
new
A light sbottom
Excess in bb cross section at the Tevatron:
How about a GeV gluino and GeV sbottom ??
P.Janot hep-ph/
 Moriond 2003: (ALEPH)
Stable sbottoms: Msbottom> 92 GeV
 Hadronic cross section data from:
LEP1, LEP2 and PEP, PETRA, TRISTAN,
95% CL lower limit on msbottom (GeV)
Small coupling sbottom to Z
The older generations in the LEP family help out (use s = GeV)
Hadronically decaying sbottom: Msbottom > 6.0 GeV
cos mix
Moriond EW 2004
Ivo van Vulpen

20. Charginos: large m0 e+ e+ e- e-  W+ l+ Small m0: light sfermions
Large cross section in large part of parameter space
 production e+ e-
Z/ e+ e-
 decay  l+ W+
Negative interference if chargino is gaugino
W-> qq (68%) / lv (32%)
1) M > 3 GeV:
LEP combined
2) 200 MeV < M < 3 GeV:
low momentum particles (use ISR -> high PT-)
3) M < 200 MeV:
‘kinky’ tracks and displaced vertices
Long lived charged particles (dE/dx information)
Moriond EW 2004
Ivo van Vulpen

21. 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 < 1 TeV and mtop = 175 GeV and no stau mixing
Moriond EW 2004
Ivo van Vulpen

22. The LSP mSUGRA MSUGRA = cMSSM + 1) common scalar mass (mA via m0)
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 
Assuming m0 < 1TeV
A=0, mtop = 175 GeV
A=0, mtop = 180 GeV
positive
negative
A any
sign() mtop
Any A mtop = 175 GeV
Moriond EW 2004
Ivo van Vulpen

23. SUSY summary:
 Not shown: AMSB & scenarios where the sneutrino or the gluino is the LSP
Moriond EW 2004
Ivo van Vulpen

24. Extra dimensions Low scale gravity in Data/MC MH> 1.20 TeV (= +1)
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 …
Moriond EW 2004
Ivo van Vulpen

25. Conclusions: Rest of the cheese is for the Tevatron & LHC
 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
Moriond EW 2004
Ivo van Vulpen

26. Backup slides
Moriond EW 2004
Ivo van Vulpen

27. Hypotheses testing: Likelihood ratio method
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(s+b)/P(b)
separating variable
 Define test-statistic as –2ln(Q), with Q = Ls+b / 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 signal+background 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 !
CLs+b: compatibility with the signal+background hypothesis
1-Clb
Cls+b
CLs: compatibility with a signal hypothesis. CLs  CLs+b/CLb
Cls < > Signal hypoth. excluded ‘at 95% CL’
Moriond EW 2004
Ivo van Vulpen

28. Charged Higgs bosons Excluded But … unfortunately
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%
Analysis: only for mA>12 GeV (bb)
mA < 12 GeV --> special effort
Extended h->AA reach (A->cc/+-/gluons)
BR(H--> )
Excluded
WW background
OPAL
Mh > 78.8 GeV (exp.)
Mh > 78.6 GeV (obs.)
Excluded
LEP1
Excluded
But … unfortunately
Included in next (final?) benchmark scan
Moriond EW 2004
Ivo van Vulpen

29. Neutralinos neutralino decay e+ e+  e- Z e-  neutralino production
SUSY Searches
Neutralinos
 neutralino production
neutralino decay  e+ e- Z e+ e- Z
Positive interference if neutralino is gaugino
Z-> qq (70%) / v v (20%) / ll(10%)
 Phenomenology depends on M, but also on m0 (common sfermion mass at GUT scale)
Moriond EW 2004
Ivo van Vulpen

30. Exotica Excluded * * e*  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…
Moriond EW 2004
Ivo van Vulpen