Searches for New Phenomena at CDF
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Transcript Searches for New Phenomena at CDF
Searches for New Phenomena at CDF
Beate Heinemann, University of Liverpool
Introduction
Supersymmetry:
Higgs
Squarks and Gluinos
Charginos and Neutralinos
Indirect search: Bsmm
Signature Based:
Dilepton and Diphoton
Diphoton+X
Summary and Outlook
MIT, March 6th 2006
The Standard Model
Matter is made out of
fermions:
quarks and leptons
3 generations
Forces are carried by
Bosons:
Electroweak: ,W,Z
Strong: gluons
Higgs boson:
Gives mass to particles
Not found yet
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H
2
What is Beyond the SM?
Many good reasons to believe there is as yet unknown
physics beyond the SM
Many possible new particles/theories:
Supersymmetry:
Extra dimensions (G)
New gauge groups (Z’, W’,…)
New fermions (e*, t’, b’, …)
Leptoquarks
Many flavours
Can show up!
As subtle deviations in precision measurements
In direct searches for new particles
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The Standard Model
only accounts for 4% of matter in Universe
No candidate for Cold Dark Matter (≈25%)
cannot explain large mass hierarchy in
fermion sector:
>10 orders of magnitude
does not allow grand unification:
electroweak and strong interactions do not
unify
Hubble Constant
There is a Lot Unknown
has large radiative corrections in Higgs
sector
Matter Density
require fine-tuning of parameters
Cannot explain matter-antimatter
asymmetry?
SM
Supersymmetry can solve three
of these problems
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What’s Nice about Susy?
Unifications of forces possible
Dark matter candidate exists:
With SUSY
The lightest neutral gaugino
Radiative corrections to Higgs
acquire SUSY corrections:
No fine-tuning required
Changes relationship between
mW, mtop and mH:
Also consistent with precision
measurements of MW and mtop
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CDF and the Tevatron
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Tevatron Run II
World’s highest energy collider
Tevatron Accelerator:
Run II
√s(TeV)
Dt(ns) L(cm-2 s-1)
1.96
396
_
p
p
1.7x1032
Key parameter: N= • Ldt
Integrated luminosity >1.5 fb-1 by
now:
CDF data taking efficiency about
83%
Delivered: 1.6 fb-1
Recorded: 1.3 fb-1
Integrate Ldt=4-8 fb-1 by 2009
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Tevatron Luminosity
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Measurement of Final State Objects with CDF
MUON CHAMBERS
h = 1.0
CENTRAL HAD CALORIMETER
END
WALL
HAD CAL.
CENTRAL EM CALORIMETER
SOLENOID
h = 2.0
h = 3.0
Silicon
Vertex
Detector
CENTRAL OUTER TRACKER
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PLUG EM CAL.
CLC
PLUG
HAD
CAL.
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Measurement of Final State Objects with CDF
Electron ID :
•Coverage : |h|<3.6
•|h|<2 (w/ trk)
•ID eff. ~ 80-90%
Photon ID :
•Coverage : |h|<2.8
•ID eff. ~ 80%
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Measurement of Final State Objects with CDF
Muon ID :
•Coverage : |h|<1
•ID eff. ~ 90-100%
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Measurement of Final State Objects with CDF
th ID
t cone
isolation
Tau ID :
•Narrow iso. cluster
•Low # tracks
• p0 identification
•Coverage : |h|<1
•ID eff. ~ 46%
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Measurement of Final State Objects with CDF
b
Jet ID :
do
•Cluster of CAL towers
Lxy
•Coverage : |h|<3.6
y
z
Heavy Flavor Jet Tagging :
x
•Id HF jets via semi-leptonic
decay
•Find soft lepton in jets
•Coverage : |h|<1
•Id HF jets via finding displaced
vertex
•Coverage : |h|<1.5
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Future High Energy Colliders
LHC (2007-?)
ILC (>2020?)
+
e
p
p
√s=14 TeV
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e√s=0.5-1 TeV
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Supersymmetry
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Supersymmetry
~
G
G
SM particles have supersymmetric partners:
Differ by 1/2 unit in spin
Sfermions (squarks, selectron, smuon, ...): spin 0
gauginos (chargino, neutralino, gluino,…): spin 1/2
No SUSY particles found as yet:
SUSY must be broken: breaking mechanism determines phenomenology
More than 100 parameters even in “minimal” models!
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How to look for SUSY
o LSP = lightest neutralino (or sneutrino or stau)
o Typical search : NLSP LSP + (SM particles), LSP
o
o
undetected : Et
Sensitivity:
o LEP: mNLSP ≈ s /2 ≤ 103.5 GeV
o Tevatron: 100- 500 GeV (depends on particle)
Example topologies:
squarks, gluinos
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chargino+neutralino
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GMSB
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Cross Section (pb)
Sparticle Cross Sections: Tevatron
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150 events
produced so
far (1.5 fb-1)
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T. Plehn, PROSPINO
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Cross Section (pb)
Sparticle Cross Sections:
LHC
100 events
with 1 fb-1
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T. Plehn, PROSPINO
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Cross Section (pb)
Sparticle Cross Sections:
LHC
100 events
with 1 pb-1
100 events
with 1 fb-1
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T. Plehn, PROSPINO
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Higgs in the MSSM
Minimal Supersymmetric Standard Model:
2 Higgs-Fields: Parameter tanb=<Hu>/<Hd>
5 Higgs bosons: h, H, A, H±
Neutral Higgs Boson:
Pseudoscalar A
Scalar H, h
Lightest Higgs (h) very similar to SM
At high tanß:
A is degenerate in mass with either h or H
Cross section enhanced with tan2b
Decay into either tt or bb for mA<300 GeV:
BR(A tt) ≈ 10%, BR(A bb) ≈ 90%
•C. Balazs, J.L.Diaz-Cruz, H.J.He, T.Tait and C.P. Yuan, PRD 59, 055016 (1999)
•M.Carena, S.Mrenna and C.Wagner, PRD 60, 075010 (1999)
•M.Carena, S.Mrenna and C.Wagner, PRD 62, 055008 (2000)
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Neutral MSSM Higgs
Production mechanisms:
Experimentally:
bb A/h/H
gg A/h/H
pp b+X bbb+X
pp +X tt +X
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MSSM Higgs: Tau-Selection
Select ttEvents:
One t decays to e or m
One t decays to hadrons
Require:
e or m with pT>10 GeV
Hadronic t:
Narrow Jet with low multiplicity
1 or 3 tracks in 10o cone
No tracks between 10o and 30o:
Cone size descreasing with increasing energy
Low p0 multiplicity
Mass<1.8 GeV
Kinematic cuts against background:
W+jets
Photon+jets
Dijets
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Acceptance and Background
Acceptance for Higgs about
1-2%
Main background:
Drell-Yan tt
Indistinguishable signature =>
Separate kinematically
No full mass reconstruction
possible for low Higgs pT:
Form mass like quantity:
mvis=m(t,e/m,ET)
Good separation between
signal and background
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MSSM Higgs: Mass Distribution
Data mass distribution agrees with SM expectation:
M>120 GeV: 8.4±0.9 expected, 11 observed
Fit mass distribution for Higgs Signal
Exclude signals at 95% C.L.
Upper limit on cross section times branching ratio
We interpret in MSSM benchmark scenarios
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MSSM Higgs: Results
pp A+X tt+X (CDF)
Sensitivity similar for
Min. and max. mixing
m>0 and m<0
pp bA+Xbbb+X (DØ)
Best sensitivity for m<0
Lower sensitivity for m>0
Nice complementarity of both modes
Particularly important if any deviation
seen in either mode
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Generic Squarks and Gluinos
Squark and Gluino
production:
jets and Et
Golden signature at LHC
(pb)
103
Missing Transverse
Energy
Jets
~g
~( s 2.0 TeV )
p pq
Missing Transverse
Energy
1
10-3
10-6
10-9
Phys.Rev.D59:074024,1999
300
( M q~ M g~ ) / 2
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500
Strong interaction => large
production cross section
for M(g)
~ ≈ 300 GeV/c2:
1000 event produced
for M(g)
~ ≈ 500 GeV/c2:
700
1 event produced
(GeV )
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Generic Squarks and Gluinos
Selection:
3 jets with ET>125 GeV, 75 GeV
and 25 GeV
Missing ET>165 GeV
HT=∑ jet ET > 350 GeV
Missing ET not along a jet direction:
QCD
Avoid jet mismeasurements
Background:
W/Z+jets with Wl or Z
Top
QCD multijets
Mismeasured jet energies lead to
missing ET
Observe: 3, Expect: 4.1±1.5
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Squark Candidate event
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Impact on SUSY
No evidence for excess of
events:
Exclude squarks and gluinos
for certain mass values
D0 excluded gluinos up to
230 GeV
CDF:
Interpretation still ongoing
Likely similar to D0
Stop and sbottom quarks
are excluded from CDF
analysis
3rd generation is special…
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3rd generation Squarks
3rd generation is special:
Masses of one can be very
low due to large SM mass
Particularly at high tanb
Direct production or from
gluino decays:
pp bb
~~ or tt~~
pp gg
~ ~ or tttt~~
~ ~ bbbb
Decay of sbottom and stop:
b b0
Stop depends on mass:
~ Heavy:
~ t t0
Medium: t b± bW0
Light: t ~c0~
~ ~
~ ~
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~
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Bottom Squarks
This analysis:
Gluino rather light: 200-300 GeV
~ ~
BR(g->bb)=100%
assumed
Spectacular signature:
4 b-quarks + ET
Require b-jets and ET>80 GeV
Expect:2.6±0.7
Observe: 4
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Exclude new parameter
space in gluino vs.
sbottom mass plane
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Light Stop-Quark: Motivation
If stop quark is light:
~ ~10
decay only via t->c
E.g. consistent with relic
density from WMAP data
Balazs, Carena, Wagner: hepph/0403224
WCDM0.110.02
m(t)-m(
~ ~ 10)≈15-30 GeV/c2
2
m(t)<165
GeV/c
~
Search for 2 charm-jets and
large Et:
ET(jet)>35, 25 GeV
ET>55 GeV
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Light Stop-Quark: Result
Charm jets:
Use “jet probability” to tag charm:
Probability of tracks originating from
primary vertex
Improves signal to background ratio:
Signal Efficiency: 30%
Background rejection: 92%
Data consistent with background
estimate
Observed: 11
Expected: 8.3+2.3-1.7
Main background:
Z+ jj -> vvjj
W+jj -> tvjj
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Stop Quark: Result and Future
Due to slight excess in data:
No limit set on stop quark mass yet
Future light stop reach :
LHC:
~
L=1 fb-1: m(t)<160
GeV/c2
L=4 fb-1: m(t)<180
GeV/c2
~
Direct production will be tough to trigger
But gluino decay to stop and top yields
striking signature!
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Two W’s, two b-quarks, two c-quarks and
missing ET
If m(g)>m(t)+m(t)
~
~
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Charginos and Neutralinos
Charginos and Neutralionos:
SUSY partners of W, Z, photon,
Higgs
Mixed states of those
Scenario here:
~
Neutralino LSP
3 leptons +
Recent analyses
Et of EWK
precision data:
J. Ellis, S. Heinemeyer, K. Olive, G.
Weiglein:
hep-ph/0411216
Light SUSY preferred
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3 leptons + Et
Many analyses to cover full phase
space:
~
10
~
1
Low tanb:
2e+e/m
2m+e/m
p
High tanb:
p
~
20
~
2e+isolated track
Sensitive to one-prong tau-decay
10
Other requirements:
Significant Et
Dilepton mass >15 GeV and not
within Z mass range
Less than 2 jets
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Trileptons: Result
Analysis
Expected
background
Example
SUSY
Data
Trilepton (mm+l)
0.090.03
0.40.1
0
Trilepton (ee+l)
0.170.05
0.50.1
0
Dielectron+track
0.490.14
1.20.1
1
Trilepton(mm+l)
0.130.03
0.12+-0.02
0
Observed event
No hint of SUSY
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Interpretation in
progress
Improve World’s limits
further
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GMSB: +Et
Assume~01 is NLSP:
~
Decay to G+
G~ light: m ≈ 1 keV
Inspired by CDF ee+Et
event in Run I
SM exp.: 10-6
D0 (CDF) Inclusive search:
2 photons: Et > 20 (13) GeV
Et > 40 (45) GeV
Exp.
Obs.
~+ )
m(
1
D0
2.5±0.5
1
>192 GeV
CDF
0.3±0.1
0
>168 GeV
D0+CDF: m(+1)> 209 GeV/c2
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Rare Decay: Bsmm
SM
heavily
BRrate
( Bs
m m suppressed:
) (3.5 0.9) 10
9
(Buchalla & Buras, Misiak & Urban)
SUSY rate may be enhanced:
(Babu, Kolda: hep-ph/9909476+ many more)
Related to Dark Matter cross section (in one of
S. Baek, Y.G.Kim, P. Ko, hep-ph/0406033
3 cosmologically interesting regions)
Recently gained a lot of attention in WMAP
data SUSY analyses, see e.g.
B. Allanach, C. Lester: hep/ph-0507383
J. Ellis et al., hep-ph/0504196
S. Baek, Y.G.Kim, P. Ko, hep-ph/0406033
R. Dermisek et al., hep-ph/0507233
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Bs
m m
vs. Trileptons
A.Dedes, S. Mrenna, U. Nierste, P. Richardson hep-ph/0507233
1x10-7
Trileptons: 2fb-1
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Indirect Search: Bs->mm
Preselection:
Two muons with pT>1.5 GeV/c
Dimuon vertex displaced from
primary
Identify variables that separate signal
from background:
Decay length:
Points towards primary vertex
Isolated from other tracks
Construct likelihood of variables:
Excellent separation
Cut at likelihood ratio >0.99
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Bs->mm :Result and Future
Result:
0 events observed
Backgrounds:
0.81± 0.12 for (CMU-CMU)
0.66 ± 0.13 for (CMU-CMX)
Branching Ratio:
CDF:
BR(Bs->mm)<1.5 x 10-7 at 90%C.L.
Combined with D0:
BR(Bs->mm)<1.2 x 10-7 at 90%C.L.
Future:
Probe values of 2x10-8
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Impact of
Bsm m
A.Dedes, S. Mrenna, U. Nierste, P. Richardson hep-ph/0507233
limits: Now
S. Baek, Y.G.Kim, P. Ko, hep-ph/0406033
Starting to constrain MSSM parameter space
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Impact of Bs
m m
A.Dedes, S. Mrenna, U. Nierste, P. Richardson hep-ph/0507233
limits: L=8
-1
fb
S. Baek, Y.G.Kim, P. Ko, hep-ph/0406033
Tevatron will severely constrain parameter space
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Impact of
Bsm m
A.Dedes, S. Mrenna, U. Nierste, P. Richardson hep-ph/0507233
limits: LHC
S. Baek, Y.G.Kim, P. Ko, hep-ph/0406033
LHC will probe SM value with about 100 fb-1
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Signature Driven Searches
All SUSY searches cover unique signatures,
e.g. I showed direct searches:
Three lepton and missing ET
3 jets and missing ET
2 b--jets or c-jets and missing ET
However, can also search really model
independent to make sure we don’t miss
anything! Examples:
Dilepton or diphoton invariant mass
Diphoton+X
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High Mass Dileptons and Diphotons
Standard Model high mass production:
New physics at high mass:
Resonance signature: Tail Enhancement:
Spin-1: Z’, W’
Spin-2: Randall-Sundrum
(RS) Graviton
Spin-0: Higgs, Sneutrino
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Contact Interactions
Large Extra Dimension
B. Heinemann
(Arkhani-Hamed,
Dimopoulos, Dvali)
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Dielectron and Diphoton Mass
Spectra
Dielectron mass
spectrum and diphoton
mass distributions
ee
Data agree well with
Standard Model
spectrum
No evidence for
mass peak
deviation in tail
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Limits on New Physics
Mass peak search examples:
Model
ZSM
Z
Z
Zh
Mass limit
(GeV/c2)
860
735
725
745
Tail enhancement: contact interaction
Probing New Physics
- Directly up to 0.9 TeV
- Indirectly up to 5-8 TeV
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Signature: Diphoton+X
Search for any objects
produced in association
with 2 photons
Electron, muon, tau
Photon
Jet
Missing ET
SM
Data consistent with
background prediction
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=e,m,
Data
+e
4.50.8
2
m
0.50.1
0
1.90.6
4
ET
0.30.1
0
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Diphoton+X: Invariant Mass
Kinematic distributions also agree well with background
prediction
Will see what happens with more data!
Triphoton analysis first physics result with >1 fb-1 of data!
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Summary and Outlook
CDF and Tevatron running
great!
Often world’s best constraints
Many unique searches of SUSY,
Higgs and new signatures
Most analyses based on up to
350 pb-1
more than 1 fb-1!
Will analyse 1 fb-1 by summer
2006
Anticipate 4.4-8.6 fb-1 by 2009
If Tevatron finds no new physics
it will provide further important
constraints
And hopefully LHC will then do the
job
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Tevatron: Future
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Backup Slides
SUSY Particles
gravitino
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Z´ee Signal Examples
Angular distribution has different sensitivity for different Z’
models
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Extra Dimensions
Attempt to solve hierarchy problem by introducing extra
dimensions at TeV scale
KK
ADD-model:
n ED’s large: 100mm-1fm
M2
PL
~
Rn
MS
q
n+2 (n=2-7)
Kaluza-Klein-tower of Gravitons continuum
Interfere with SM diagrams: =±1 (Hewett)
_
q
ee,
mm,
Randall Sundrum:
Gravity propagates in single curved ED
ED small 1/MPl=10-35 m
Large spacing between KK-excitations
resolve resonances
Signatures at Tevatron:
Virtual exchange:
2 leptons, photons, W’s, Z’s, etc.
BR(G->)=2xBR(G->ll)
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Randall-Sundrum Graviton
Analysis:
2 photon mass spectrum
Backgrounds:
direct diphoton production
Jets: p0
Data consistent with
background
Relevant parameters:
Coupling: k/MPl
Mass of 1st KK-mode
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Dirac Magnetic Monopole
•Bends in the wrong plane ( high pt)
•Large ionization in scint (>500 Mips!)
•Large dE/dx in drift chamber
mmonopole > 350 GeV/c2
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Neutral Spin-1 Bosons: Z’
2 high-PT electrons, muons, taus
Data agree with BG (Drell-Yan)
Interpret in Z’ models:
E6-models: ,h,, I
SM-like couplings (toy model)
QuickTime™ and a
TIFF (LZW) decompressor
are needed to see this picture.
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3-lepton Event
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