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Exploring the Unknown UniverseDaniel Whiteson, UC Irvine
MotivationThe Standard Model
Can this be right?
Outline
I. MotivationII. StrategyIII. Results
Searching for new physicsModel
Search strategySpec
ific
Gen
eral
Our goals:- Maximize possibility for discovery- Learn something no matter what we see
Traditional approach
Bet on a specific full theoryOptimize analysis to squeeze out maximal sensitivity to new physics.
param 1
para
m 2 (param 3-N fixed at arbitrary choices)
Model
Search strategySpec
ific
Gen
eral
Model independent search
Discard the modelcompare data to standard model
Model
Search strategySpec
ific
Gen
eral
“Never listen to theorists. Just go look for it”
--Aaron Pierce, Theorist
Compromise
Admit the need for a modelNew signal requires a coherent physical explanation,
even trivial or effective
Generalize your modelFocus on the general experimental sensitivityConstruct simple models that describe classes of new physics
ExamplesSimple SM extensions: fourth generation, Z’, resonances (X->tt) etc
Model
Search strategySpec
ific
Gen
eral
Effective LagrangianA natural, compact language for communication between theory and experiment.
Experimental data
Full Theory
Full Theory
Full Theory
Full Theory
Full Theory
Full Theory
Limits or measurements
on effective Lagrangian parameters
A Theorist’s dream?Unfolded cross-sectionsDeconvolution to remove detector effects
Publish measured differential cross-sections
Theorists don’t need to know/have detector description
This is hard!
Outline
I. MotivationII. StrategyIII. Results a. Heavy resonances (Z’) b. Heavy quarks (b’, t’) c. Simplified SUSY
CDF
Dataset
High mass resonances
Z’ to di-muons
UCI UndergradEddie Quinlan
High mass dimuon res.
]2 [GeV/c!!M200 400 600 800 1000 1200
Even
ts
-210
-110
1
10
210
310
410
510
Data
*!Z/
tt
WW
Fakes
Cosmics
-1CDF Run II Preliminary 4.6 fb
]2 [GeV/cµµM200 400 600 800 1000 1200
(Obs’
d -
Exp’d
)/
Exp’d
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
-1CDF Run II Preliminary 4.6 fb
PRL 2011, to appear
Z’ to muons
PRL 2011, to appear
Z’ to muons
PRL 2011, to appear
Z’ to muons
]2
Z’ mass [GeV/c
200 300 400 500 600 700 800 900 1000 1100
) [p
b]
!!
!(Z
’) *
BR
(Z’
"
-310
-210
95% CL limit
IZ’
secZ’
NZ’
#Z’
$Z’
%Z’
SMZ’
-1CDF Run II Preliminary 4.6 fb
PRL 2011, to appear
ATLAS Z’ Penn +other groups
Limits Penn +other groups
Limits Penn +other groups
Outline
I. MotivationII. StrategyIII. Results a. Heavy resonances (Z’) b. Heavy quarks (b’, t’) c. Simplified SUSY
4th generationPDG says it’s
ruled out to 6σ....
4th generation
[GeV]d4-mu4m
-150 -100 -50 0 50 100 150
[G
eV
]4!
-ml4
m
-150
-100
-50
0
50
100
150 ) [%
]2"
#P
rob(
-110
1
10
projects.hepforge.org/opucem/
PDG says it’s ruled out to 6σ....
..that’s true if the masses are degenerate
t’Selection1 lepton
pt>20 GeV4 jets pt>20 GeV
Missing transverse energy >20 GeV
Sample4.6/fb
28
UC Davis
t’
Limitmt’ > 335 GeV
29
UC Davis
b’Selection2 like-signed leptons
pt>20 GeVat least one isolated
2 jets pt>20 GeV >=1 btagsMissing transverse energy >20 GeV
Sample2.7/fb
UCI UndergradMatt Hickman
PRL 104 091801 (2010)
b’Final selection2 like-signed leptons 2 jets >=1 btags
Missing transverse energy
PRL 104 091801 (2010)
mb’ > 338 GeV
b’ decaysIf b’ -> Wt
same-sign lepton selection: ~2%consider single-lepton mode
32
UCI undergradReza AmirArjomand
Signal (madgraph)
33
Number of jets0 2 4 6 8 10
Fra
ctio
n o
f E
ven
ts
0
0.05
0.1
0.15
0.2
0.25=300
b’m
=350b’
m
=400b’
m
CDF Run II Preliminary
[GeV]TH
0 200 400 600 800 1000
Fra
ctio
n o
f E
ven
ts
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
CDF Run II Preliminary
Eight hard partons, ~6 jets
Signal (madgraph)
34
Number of jets0 2 4 6 8 10
Fra
ctio
n o
f E
ven
ts
0
0.05
0.1
0.15
0.2
0.25=300
b’m
=350b’
m
=400b’
m
CDF Run II Preliminary
[GeV]TH
0 200 400 600 800 1000
Fra
ctio
n o
f E
ven
ts
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
CDF Run II PreliminaryHTScalar sum of transverse energy in the event
Includes jets, lepton and missing transverse energy
Captures soft recoil and unclustered jets
top quark pair backgroundtt + 0,1,2,3p p = udscbMadgraph+PythiaMLM matching
35
TJet-H
0 1000 2000 3000
Ev
ents
-210
-110
1
10
210Backgrounds
=350b’
b’, m
CDF Run II Preliminary
Analysis techniqueEventsheavy and jetty
Analysis variable
normalized to 5/fb36
5j6j 7j+
Data, >=1 b-tag
37
5j6j
7j+
The numbers
38
The limits
39
Direct searches
mb’ > 372 GeV mt’ > 335 GeV
replace
Direct searches
mb’ > 372 GeVIf BR(b’ →Wt)=100%
mt’ > 335 GeVIf BR(t’ →Wq)=100%
b’ l+j
b’ and t’
If mt’ > mb’
u c t t’d s b b’
PRL 2010, PRD 2011
UCI undergradMatt Kelly
UCI postdocChristian Flacco
b’ and t’
PRL 2010, PRD 2011
b’ and t’CDF limits
u c t t’d s b b’
PRL 2010, PRD 2011
b’ and t’
No direct limits!PRL 2010, PRD 2011
t’ and b’
mt’ = mb’ + 100 mt’ = mb’ + 50PRL 2010, PRD 2011
Limits
V44
V34
290300
PRL 2010, PRD 2011
heavy quarks
mQ’ > 290 GeV
If the lifetime is short enough so the decay is in the central detector:
PRL 2010, PRD 2011
ATLAS t’Selection2 OS leptons
pt>20 GeV2 jets pt>20 GeV
Missing transverse energy >20 GeV
Sample35/pb
UCI grad studentMichael Werth
topology
tb
Wt
b
W
Boosted tops
topology
tb
Wt
b
W
t’b
W
t’b
W
Boosted Ws!
Lepton-neutrino anglesHeavy t’ SM top
WMore W pT means smaller opening angle
Mass reconstructionAssume lepton and neutrino are ~collinear
Data
No sign of heavy quarks...
Limit
Limitmt’ > 275 GeV
Limit
Limitmt’ > 275 GeV
First LHC t’ li
mits
First t’ d
ilepton search
Dark MatterNeed long lived dark matter X
Dark Matter
Dark Matter XSM ParticlesSM Charges Dark Charge
Need long lived dark matter XGive it some dark charge that is conserved(eg R-parity for susy LSP)
Dark Matter
Dark Matter XSM ParticlesSM Charges Dark Charge
Need long lived dark matter XGive it some dark charge that is conserved(eg R-parity for susy LSP)
X can’t be light (~< 10 GeV) and carry SM charges to be consistent with relic density.
Dark Matter
Dark Matter XSM Particles
Connector Y
SM Charges
SM Charges
Dark Charge
Dark Charge
Need long lived dark matter X
Produce Y, decay as Y -> f X
Dark Matter+4th genUCI grad studentKanishka Rao
Look for ttbar + invisible XT’ -> t+Xstop -> t + LSP
Transverse mass
Limits
Outline
I. MotivationII. StrategyIII. Results a. Heavy resonances (Z’) b. Heavy quarks (b’, t’) c. Simplified SUSY
SUSY
GoalSet limits on SUSY-like processes in as general a fashion as possible
ApproachUse effective lagrangian, explicitly set particle masses (EW scale):
simple to handle, easy to interpret
Set limits as functions of these masses, not parameters of specific models: can be easily translated into arbitrary models
How?How many particles & parameters needed?Want leptons needs Ws and Zs, so chargino/neutralinos and sleptons
Want strong production so squarks and gluinos
R-Parity conserving need LSP
Large sections of this space are 3 or 4-dimensional
SUSY simplified UCI postdocNing Zhou
SS SUSY simplified UCI postdocNing Zhou
CDFStill producing world-class physics
ATLASWorking well, much more to come