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Highlights of the searches for Higgs bosons at LEP2. Marumi Kado CERN. First hints of Higgs boson production. Part I. 206.5 GeV. 205 GeV. How it all began. June 14 th : First candidate at high energy and high reconstructed mass (~115 GeV/c2 ~ 206.5-m Z ). - PowerPoint PPT Presentation
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22/01/2001 Marumi Kado - CERN 1
Highlights of the Highlights of the searches for Higgs searches for Higgs
bosons at LEP2bosons at LEP2
Marumi KadoMarumi KadoCERNCERN
22/01/2001 Marumi Kado - CERN 2
First hints of Higgs boson First hints of Higgs boson productionproduction
Part I
22/01/2001 Marumi Kado - CERN 3
205 GeV205 GeV
206.5 GeV206.5 GeV
22/01/2001 Marumi Kado - CERN 4
How it all beganHow it all began
July 20July 20thth LEPC: LEPC: First combinationFirst combination limit limit 113.3113.3 GeV/cGeV/c22 / /sensitivity sensitivity 113.4 GeV/c113.4 GeV/c22
June 14June 14thth: : First candidateFirst candidate at high energy and high at high energy and high reconstructed mass reconstructed mass (~115 GeV/c2 ~ (~115 GeV/c2 ~ 206.5-m206.5-mZZ))
September 5September 5thth LEPC: LEPC: Second combinationSecond combination A A 2.22.2 excess is observed excess is observed limit limit 112.3112.3 GeV/cGeV/c22 / /sensitivity sensitivity 113.8 GeV/c113.8 GeV/c22
22/01/2001 Marumi Kado - CERN 5
Septembre 14th Research board: Septembre 14th Research board: LEP is awarded an LEP is awarded an additional month of running, to further check these additional month of running, to further check these results results
Octobre 10Octobre 10thth LEPC: LEPC: Update of the resultsUpdate of the results The September 5The September 5thth excess grows up to excess grows up to 2.62.6
November 2November 2dd: : end of LEP operationsend of LEP operations
November 3November 3dd LEPC: LEPC: The new data confirm the The new data confirm the excess again. The significance grows up to excess again. The significance grows up to 2.92.9
November 13November 13thth:: ALEPH publication ALEPH publication November 14November 14thth:: L3 publication L3 publication
December 22December 22dd:: OPAL and DELPHI publication OPAL and DELPHI publication
Repeated confirmationsRepeated confirmations
Additional 2001 running not grantedAdditional 2001 running not granted
LEP running in 2001 is requested LEP running in 2001 is requested
22/01/2001 Marumi Kado - CERN 6
Radiated by a Z* (Higgs-strahlung)Radiated by a Z* (Higgs-strahlung)
Production process at LEPProduction process at LEP
«Threshold»«Threshold»
204202
208206
s-mZs-mZ
~ 0.04 pb
as a fonction of mH
en fonction de s
Dominant production process
ee++ee- - HZ HZ 3 Sensitivity:mH s-mZ
5
3 L~200pb-1
22/01/2001 Marumi Kado - CERN 7
DecaysDecays
Higgs boson branching ratiosHiggs boson branching ratios
LEP has mostly LEP has mostly b quarkb quark or or leptonlepton
Gain sensitivity near 115 GeV/cGain sensitivity near 115 GeV/c22 OPAL and L3 have OPAL and L3 have also started the study of Walso started the study of W++WW- - decays of the Higgs decays of the Higgs bosonboson
For mmHH ~ 115 GeV/c ~ 115 GeV/c22
Br(Hbb) ~ 74%Br(H+-) ~ 7%
Br(HW+W-) ~ 7%
22/01/2001 Marumi Kado - CERN 8
Background processesBackground processes
Doubly resonant production of W and Z bosonsDoubly resonant production of W and Z bosons
A priori irreducible processZbb~2 pb
Reducible process~15 pb
_
22/01/2001 Marumi Kado - CERN 9
Search topologiesSearch topologies
Mainly determined by the Z boson decay modesMainly determined by the Z boson decay modes
The “four jets” topologyThe “four jets” topology
%70)qqZ(
qqZ bbH
Dominant channel:
Background processes near threshold:
b quark pair with2 hard gluons
Quark pair withgluon splitting into a quark pair
b
b_
q_
q
22/01/2001 Marumi Kado - CERN 10
Missing energy channelMissing energy channel
%20)Z(
ZbbH
Second most prolific channel:
Main background near threshold:
Where the Higgs boson is produced alsoin the fusion process:
b quark pair2 photons ISR
2 ISR escape undetected
at low angle
non-negligible contribution near threshold
(Constructive interference) No kinematic threshold
b_
b
_
22/01/2001 Marumi Kado - CERN 11
Leptonic channelsLeptonic channels
),e(
%7)Z(
Z
Good resolution in reconstructed mass:
)Z,bbH(
The H or Z decays to taus:
bbH
)qqZ,H(
Also produced by the fusion process:
Negligible contribution(destructive interference)
%7
b_
b,q_
b
b,q
e+,+
e-,-
+
-
ZbbH
ZqqZ
_
22/01/2001 Marumi Kado - CERN 12
Combined resultsCombined results
Results as ofResults as of November 3 November 3dd
DELPHI TPC sector and OPAL VDET module problems were worked around
Analysed luminosity up to October 25Analysed luminosity up to October 25thth
The The ~30 pb~30 pb-1-1 collected between collected between 25/1025/10 and and 02/1102/11 are not are not included in this combinationincluded in this combination
Luminosité intégrée (pb-1)Expérience
>200 GeV >206 GeV
ALEPH 122
DELPHI206214 132
L3 201 124
OPAL 190 110
Total LEP 810 488
s s
22/01/2001 Marumi Kado - CERN 13
Illustration of the searches Illustration of the searches resultsresults
Reconstructed mass histogramsReconstructed mass histograms
Rescalings or fits using the recoil to the Z boson
Each Each channelchannel in each in each experimentexperiment is optimized with different is optimized with different expected background ratesexpected background rates
A possible prescription to illustrate the results of the searches is:A possible prescription to illustrate the results of the searches is:
So that each channel and each experiment are represented in a fair way:
S/B for a Signal mass of mH=115 GeV/c2 and for a reconstructed mass greater than 109 GeV/c2
Fixed S/B ratio
These histograms are shown for illustration These histograms are shown for illustration purposes only purposes only they do not containthey do not contain all the all the
information used in the complete information used in the complete interpretation of the resultsinterpretation of the results
22/01/2001 Marumi Kado - CERN 14
Reconstructed mass distribution (S/B>0.3)Reconstructed mass distribution (S/B>0.3)
MH=115 GeV/c2 Full spectrum MH>109GeV/c2
Signal 10.3 6.1
Background 202 20.4
Data 200 27
Good agreement data and Monte Carlo
Excess at high reconstructed mass
26.5
22/01/2001 Marumi Kado - CERN 15
For S/B>1For S/B>1
High mass excessconfirmed
MH=115 GeV/c2 Full spectrum MH>109GeV/c2
Signal 4.7 3.0
Background 55.3 3.6
Data 59 6
6.660
22/01/2001 Marumi Kado - CERN 16
For S/B>2For S/B>2
MH=115 GeV/c2 Full spectrum MH>109GeV/c2
Signal 2.7 1.8
Background 22.8 1.1
Data 24 4
2.925.5
ALEPH: 3 (4J) L3: 1 (H)
Most significantevents
(mH>109 GeV/c2)
High mass excessagain confirmed
22/01/2001 Marumi Kado - CERN 17
Estimation of an experiment Estimation of an experiment s, b, Ns, b, N
Estimator Estimator Likelihood ratio: Likelihood ratio:
Complete interpretationComplete interpretation
N
1i i
isN
1i i
iib
)bs(
b
bs
b~s~
1eb~
b~
s~
e
eL
LQ
- si signal local value of the discriminating variable (reconstructed mass, b-tag, NN)
- bi local value for the expected background
~
~
N
1i
ii)bs(N
bs bsb~
s~e
!N)bs(
L
N
1i
ibN
b bb~
e!N
bL
Likelihood for the signal & background hypothesis
Likelihood for the background only hypothesis
For each event i:For each event i:
ALEPH
22/01/2001 Marumi Kado - CERN 18
-2lnQ-2lnQ Estimator used Estimator used
Trivial combination of channels and experimentsTrivial combination of channels and experiments (Sum of the estimators)(Sum of the estimators)
For gedanken experiments:For gedanken experiments:
Signal & bckg. Bckg. only
Light Higgs and large cross section
Intermediate Higgs mass and cross section
Heavy Higgs andlow cross section
N
1ii )ws(2Qln2 where )
b~s~
1ln(wi
ii
22/01/2001 Marumi Kado - CERN 19
Estimator for each Estimator for each experimentexperiment
For different Higgs boson mass hypotheses:For different Higgs boson mass hypotheses:
A, L & O: Significant excess at high massO: Also excess ~105 GeV/c2
D: Deficit
22/01/2001 Marumi Kado - CERN 20
Back to the transverse vue Back to the transverse vue for mfor mHH=115 GeV/c=115 GeV/c22
The distribution of the four observations is The distribution of the four observations is compatiblecompatible with the signal hypothesis with the signal hypothesis
Illustration of the signal & background and Illustration of the signal & background and background only expectations for mbackground only expectations for mHH=115 GeV/c=115 GeV/c22
-2lnQ -2lnQ
-2lnQ-2lnQ
22/01/2001 Marumi Kado - CERN 21
Combined estimatorCombined estimator
Minimum at 115 GeV/cMinimum at 115 GeV/c22 in in coincidence coincidence with the most likely value in the signal with the most likely value in the signal
and background hypothesisand background hypothesis
mmHH=115 GeV/c=115 GeV/c22+0.7+0.7-0.3-0.3
-2lnQ
-2lnQ
Q ~ 30Q ~ 30
22/01/2001 Marumi Kado - CERN 22
How much do we trust that this observation is How much do we trust that this observation is background like?background like?
CLCLbb Official « discovery » estimator Official « discovery » estimator (deviation from (deviation from the Standard Model)the Standard Model)
CLb: Fraction of background only “gedanken” experiments with an estimator larger than observed
-2lnQ observed
Confidence in the background hypothesis
Confidence levelConfidence level
2.9 Standard 2.9 Standard deviationsdeviations
(m(mHH=115 GeV/c=115 GeV/c22))
1-Cl1-Clbb = 4.2 10 = 4.2 10-3-3
Minimum at 115GeV/c2:
22/01/2001 Marumi Kado - CERN 23
Most significant candidatesMost significant candidates
(s/ b)115 Mrec(GeV/ c2) Chanel Exp.
4.7 114 (d) Hqq ALEPH
2.3 112 (c) Hqq ALEPH2.0 114 (b) H L30.90 110 (a) Hqq ALEPH0.60 118 Hee ALEPH0.52 113 Hqq OPAL0.50 111 Hqq OPAL*0.50 115 H ALEPH0.50 115 Hqq ALEPH0.49 114 H L30.47 115 Hqq L30.45 97 Hqq DELPHI0.40 114 Hqq DELPHI0.32 104 H OPAL
ALEPH: 6ALEPH: 6L3: 3L3: 3
OPAL: 3OPAL: 3DELPHI: 2DELPHI: 2
Hqq: 9Hqq: 9HH: 3: 3HlHl++ll--: 1: 1HH: 1: 1
(70%(70%))
(20%(20%))
(7%)(7%)(3%)(3%)
TheoreticalTheoreticalbranchingsbranchings
Candidates with (s/b)Candidates with (s/b)115115>0.3 >0.3 Observed: Observed: 1414Expected (s+b): Expected (s+b): 1414Signal: Signal: 77
22/01/2001 Marumi Kado - CERN 24
Candidate -a- (21/08/2000)Candidate -a- (21/08/2000)
e+e-bbbb_ _
s = 206.7s = 206.7
Mrec=1103 GeV/c2
Three well b-tagged jetswith two reconstructed
displaced vertices
22/01/2001 Marumi Kado - CERN 25
L3L3
ee++ee--bbbb206.6 GeV
Mrec
114.4 GeV/c114.4 GeV/c22
Missingmass
94 GeV/c94 GeV/c22
Candidate -b- (16/10/2000)Candidate -b- (16/10/2000)
Two b-tagged jets
with two reconstructe
ddisplaced vertices
(5 mm and 1 mm)
22/01/2001 Marumi Kado - CERN 26
Candidate -c- (31/07/2000)Candidate -c- (31/07/2000)
e+e-bbbb_ _
s = 206.7s = 206.7
Mrec=1123 GeV/c2
Four well b-tagged jetswith tree reconstructed
displaced vertices
22/01/2001 Marumi Kado - CERN 27
Candidate -d- (14/06/2000)Candidate -d- (14/06/2000)
Directionimpulsion manquante
e+e-bbqq_ _
s = 206.7s = 206.7
Mrec=1143 GeV/c2
Two well b-tagged jetswith two reconstructed
displaced vertices
22/01/2001 Marumi Kado - CERN 28
How about the less significant How about the less significant events?events?
A: (s/b)115<0.7 B: (s/b)115>0.7
-2lnQA -2lnQB~
The effect is not The effect is not only due to the only due to the
four most four most significant eventssignificant events
22/01/2001 Marumi Kado - CERN 29
Estimator for each channelEstimator for each channel
Excess at high Higgs mass hypotheses in all channels
most significant in the 4 jets channel
As a function of the Higgs boson mass hypothesis:As a function of the Higgs boson mass hypothesis:
22/01/2001 Marumi Kado - CERN 30
All channels are All channels are compatiblecompatible with the signal with the signal hypothesishypothesis
-2lnQ-2lnQ
-2lnQ -2lnQ
Back to the transverse vue Back to the transverse vue for mfor mHH=115 GeV/c=115 GeV/c22
22/01/2001 Marumi Kado - CERN 31
Evolution of the effect with Evolution of the effect with timetime
1.1
2.2
2.6
2.9
Results coherent with the presence of Results coherent with the presence of a Higgs boson with mass 115 GeV/ ca Higgs boson with mass 115 GeV/ c22
Coherence in terms of
amounts of datataken at high energy
Coherence in terms of
independent samples
22/01/2001 Marumi Kado - CERN 32
Could there be a systematic bias Could there be a systematic bias near threshold?near threshold?
Question mainly answered by looking at data taken at Question mainly answered by looking at data taken at lower centre-of-mass energies:lower centre-of-mass energies:
Observed estimator as a functionof the distance to threshold
with 500pb-1 (per experiment) of data taken between 183
and 206 GeV
If a bias similar tothat observed above
206 GeVwas observed at all
centre-of-mass energies
22/01/2001 Marumi Kado - CERN 33
Summary of the Standard Summary of the Standard Model Higgs search as of Model Higgs search as of
November 3November 3dd LEPC LEPC
Each experiment has a 3Each experiment has a 3sensitivity between sensitivity between 111.5111.5 and and 113.5 GeV/c113.5 GeV/c22
The combined sensitivity of the four experiments The combined sensitivity of the four experiments reaches reaches 33at at mmHH=115 GeV/c=115 GeV/c22
Coherent picture:Coherent picture:
Four experimentsAll channelsIn terms of production (threshold effect)Evolution in time and amount of accumulated data
Can we exclude? Can we exclude? LEP (rhetorical question) sensitivity 115.3, mH>113.5 GeV/c2 DELPHI sensitivity 113.4, mH>113.9 GeV/c2
A 3A 3 excess is observed by the combination excess is observed by the combination in agreement with the production of a Higgs in agreement with the production of a Higgs
boson weighing 115 GeV/cboson weighing 115 GeV/c22 +0.7+0.7-0.3-0.3
22/01/2001 Marumi Kado - CERN 34
What have we learned since?What have we learned since? ALEPH ALEPH (PLB 495(2000)1):(PLB 495(2000)1):
- Combination: excess of 3.4/ published 3.0. Due to mainly two effects:
- Additional luminosity - Taking into account correlation between discriminating
variables
OPAL OPAL (CERN-EP-2000-156):(CERN-EP-2000-156): In the combination the significance was 1.3, but a quite significant event was detected after October 25th:
DELPHIDELPHI (to appear in PLB) : (to appear in PLB) : Observed limit 113.9114.3 GeV/c2
Expected limit 113.4113.5 GeV/c2
L3 L3 (PLB 495(2000)18):(PLB 495(2000)18): Reprocessing and analysis work is being completed.
OpalOpal
ee++ee--bbbbqqqq
29 Oct. 2000206.6 GeV
Mrec= 110.5 110.5 GeV/cGeV/c22
(1-Clb)03/11/2000=0.19(1-Clb)published=0.2
22/01/2001 Marumi Kado - CERN 35
Beyond the Minimal Beyond the Minimal Standard ModelStandard Model
(Review of the topologies studied)(Review of the topologies studied)
Part II
22/01/2001 Marumi Kado - CERN 36
Non minimal extensions of Non minimal extensions of the Standard Modelthe Standard Model
Any number of Higgs doublets is adequate to break Any number of Higgs doublets is adequate to break the EW symmetry the EW symmetry ((=1 at tree level)=1 at tree level)
Using two complex scalar Higgs doubletsUsing two complex scalar Higgs doublets Mass to gauge bosons and Five physical scalar fields are
left: h,H (CP even), A (CP odd) and H
The 6 free parameters of the model are: - Higgs masses - mixing between h and H - tan : ratio of the vev of the two doublets
To avoid FCNC fermions of a given charge must couple at most to one doublet only. There are therefore only two convenient types of models:
- Type I: One doublet does not couple to fermions -Type II: One doublet couples only to “up” type
fermions and the other to “down” type fermions.
22/01/2001 Marumi Kado - CERN 37
In general In general 2HDM2HDM: Search for charged Higgs bosons: Search for charged Higgs bosons
The two main decay channels areThe two main decay channels are H H /cs/cs
ProductionProduction
Model dependence is embedded in Model dependence is embedded in BrBr(H (H )) assuming assuming
Topologies searched for:
cscs cs
Main background: W pair production
]1)csH()H([ BrBr
22/01/2001 Marumi Kado - CERN 38
The L3 excessThe L3 excess
2000 L3 data confirm and reinforce this effect, but...2000 L3 data confirm and reinforce this effect, but...
PLB496(2000)34
Effect consistently seen at all centre-of-massenergies above 189 GeV
22/01/2001 Marumi Kado - CERN 39
the effect is not confirmed by other experiments: the effect is not confirmed by other experiments: Each Each experiment individually excludes a possible signal atexperiment individually excludes a possible signal at
~70 GeV/c~70 GeV/c22
The combined exclusion in the The combined exclusion in the (m(mHH, Br(H , Br(H )))) as of as of
September 5September 5th th LEPC (with data since 1998):LEPC (with data since 1998):
(LEPC 05/09/2000)
22/01/2001 Marumi Kado - CERN 40
In the In the 2HDM type I2HDM type I, if cos, if cos=0 then no mixing occurs =0 then no mixing occurs between the two CP-even Higgs bosons, thus one will between the two CP-even Higgs bosons, thus one will not couple to fermions whatsoever (fermiophoby)not couple to fermions whatsoever (fermiophoby)
- Produced by Higgs-strahlung process - Decays to a pair of photons if mh is small compared to 2mW
Topologies searched for:
qq~70% ~20% ~3%ll~7%
mqq~mZ m~mZ m,ll~mZ
Main background: two fermions production with two photons
Mass lower limit on a Higgs boson decaying to a pair of photons:107.7 GeV/c2 (obs)105.8 GeV/c2 (exp)
(LEPC 05/09/2000)
22/01/2001 Marumi Kado - CERN 41
2HDM II, Flavour independent analyses (OPAL)2HDM II, Flavour independent analyses (OPAL)
- For certain parameter choices ( and tan0), the decay modes to a pair of b quarks and tau leptons can be suppressed
- Production process: Higgs-strahlung MSM
qqqq,qqgg~70% qq,gg~20% qq,gg~3%qq,ggll~7%
mqq~mZ m~mZ m,ll~mZ
Main backgrounds: Four fermion production
Mass lower limit on a Higgs boson decaying to any
quark flavour or a gluon pair:
75 GeV/c2 (obs)89.5 GeV/c2 (exp)
mh
CERN-EP-2000-92OPAL
170pb-1@183 and 189 GeV
Quasi model independent interpretation:
22/01/2001 Marumi Kado - CERN 42
A complete 2HDM type II interpretation, the associated A complete 2HDM type II interpretation, the associated production has also been studied:production has also been studied:
Interpretation independent of the parameter Interpretation independent of the parameter ::
Associated production
Flavor independent
Standardsearches
Ingredients:
Flavourindependent
FlavourdependentNo mass constraints
22/01/2001 Marumi Kado - CERN 43
The MSSMThe MSSM
A 115 GeV/A 115 GeV/ cc22 Higgs boson invites SUSY Higgs boson invites SUSY (J. Ellis and D. Ross (J. Ellis and D. Ross hep-ph/0012067)hep-ph/0012067)
The MSSM Higgs sector is a 2HDM type II, with only two The MSSM Higgs sector is a 2HDM type II, with only two free parameters at tree level (free parameters at tree level (mmAA and and tantan). ).
- mH< 130 GeV/c2 - At higher orders: Large number of parameters Most
conservative benchmark maximal mh
Topologies searched for to cover the High tanTopologies searched for to cover the High tan region region h/A h/A bb/ bb/ with with mmhh~m~mAA
bbbb~85% bb+- ~13%
ComplementaryProduction processes:
Higgs-strahlungsin2(-)
Associatedcos2(-)
Use standard searches
22/01/2001 Marumi Kado - CERN 44
Exclusion regions Exclusion regions (combined as of October 10(combined as of October 10thth LEPC) LEPC)
The robustness of the limits on the masse of the h and A The robustness of the limits on the masse of the h and A Higgs bosons has been proven by large scans of all relevant Higgs bosons has been proven by large scans of all relevant parameters of the MSSM parameters of the MSSM (Eur. Phys. J. C 17(2000)223)(Eur. Phys. J. C 17(2000)223)
TheThe tan tan exclusion range is very sensitive to the top mass It exclusion range is very sensitive to the top mass It can be drastically reduced by assuming a large top masscan be drastically reduced by assuming a large top mass
tan exclusion [0.52,2.25]/expected [0.48,2.48]
mh> 89.9 (obs.) 93.8 (exp.) GeV/c2
mA> 90.5 (obs.) 94.1 (exp.) GeV/c2
22/01/2001 Marumi Kado - CERN 45
Beyond… Beyond… Invisible decays of Higgs bosonsInvisible decays of Higgs bosons can occur in different can occur in different
models:models: - MSSM with non universal gaugino masses - Models with majorons
Produced by Higgs-strahlung processProduced by Higgs-strahlung process
Quasi model independent interpretation:Quasi model independent interpretation:
qq (invisible) ~70% ll (invisible) ~7%
Main backgrounds:Four fermions
MSMhZ
hZ2 )invisibleh( Br
For=MSM
Br(hinv.) = 100%
mh> 113.7 (obs.) mh> 112.8 (exp.)LEP
CombinationLEPC 05/09/2000
22/01/2001 Marumi Kado - CERN 46
Anomalous couplings:Anomalous couplings: Assuming new physics appear at Assuming new physics appear at a scale a scale , low energy effects can be parametrised with , low energy effects can be parametrised with an effective Lagrangian:an effective Lagrangian:
nn
2n
eff Of
L
Where On are combinations of Higgs and Gauge fields
Anomalous couplings of the type h and hZ, are allowed
Hypotheses: One Higgs doublet and C and P conservation
Topologies:
22/01/2001 Marumi Kado - CERN 47
DELPHIDELPHI search up to 183 GeV search up to 183 GeV (PLB 458(1999)431)(PLB 458(1999)431) interpretation (All finterpretation (All fnn’s are equal to F)’s are equal to F)
22/01/2001 Marumi Kado - CERN 48
Interpretation of Interpretation of ALEPHALEPH’s MSM and Fermiophobic ’s MSM and Fermiophobic Higgs boson searches up 202 GeV Higgs boson searches up 202 GeV (Moriond QCD 2000)(Moriond QCD 2000)
Also Also L3L3 search @189 GeV search @189 GeV (PLB 489(2000)102)(PLB 489(2000)102) with with additional interpretationsadditional interpretations
22/01/2001 Marumi Kado - CERN 49
ConclusionsConclusions
Numerous theoretical scenarios were investigated at Numerous theoretical scenarios were investigated at LEP and many nonstandard topologies, where the Higgs LEP and many nonstandard topologies, where the Higgs
boson could have escaped otherwise, were covered boson could have escaped otherwise, were covered
Hints of a 115 GeV/cHints of a 115 GeV/c22 standard-model-like Higgs boson standard-model-like Higgs boson were observed, as strong as could be expected at such were observed, as strong as could be expected at such
high mass, close to the operational limit of LEPhigh mass, close to the operational limit of LEP
This observation corresponds to roughly 3 standard This observation corresponds to roughly 3 standard deviations above the background expectationdeviations above the background expectation
These indications are not sufficient to claim a discovery These indications are not sufficient to claim a discovery
An additional year of LEP running in 2001 would have An additional year of LEP running in 2001 would have been essential to concludebeen essential to conclude
(Final results are scheduled for the forthcoming winter (Final results are scheduled for the forthcoming winter conferences)conferences)
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