Exploring the Unknown Universe Daniel Whiteson, UC Irvine - - PowerPoint PPT Presentation

Exploring the Unknown Universe

Daniel Whiteson, UC Irvine

Motivation

The Standard Model

Can this be right?

Outline

• I. Motivation
• II. Strategy
• III. Results

Searching for new physics

Model Search strategy

Specific General

Our goals:

• Maximize possibility for discovery
• Learn something no matter what we see

Traditional approach

Bet on a specific full theory

Optimize analysis to squeeze out maximal sensitivity to new physics.

param 1 param 2

(param 3-N fixed at arbitrary choices)

Model Search strategy

Specific General

Model independent search

Discard the model

compare data to standard model

Model Search strategy

Specific General

“Never listen to theorists. Just go look for it”

• -Aaron Pierce, Theorist

Compromise

Admit the need for a model New signal requires a coherent physical explanation, even trivial or effective Generalize your model Focus on the general experimental sensitivity Construct simple models that describe classes of new physics Examples Simple SM extensions: fourth generation, Z’, resonances (X->tt) etc

Model Search strategy

Specific General

Effective Lagrangian

A 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

• n effective

Lagrangian parameters

A Theorist’s dream?

Unfolded cross-sections Deconvolution to remove detector effects Publish measured differential cross-sections Theorists don’t need to know/have detector description This is hard!

Outline

• I. Motivation
• II. Strategy
• III. Results
• a. Heavy resonances (Z’)
• b. Heavy quarks (b’, t’)
• c. Simplified SUSY

CDF

Dataset

High mass resonances

Z’ to di-muons

UCI Undergrad Eddie Quinlan

High mass dimuon res.

]

2

[GeV/c

! !

M

200 400 600 800 1000 1200

Events

• 2

10

• 1

10 1 10

2

10

3

10

4

10

5

10

Data

*

! Z/ tt WW Fakes Cosmics

• 1

CDF Run II Preliminary 4.6 fb

]

2

[GeV/c

µ µ

M

200 400 600 800 1000 1200

(Obs’d - Exp’d )/ Exp’d

• 1
• 0.8
• 0.6
• 0.4
• 0.2

0.2 0.4 0.6 0.8 1

• 1

CDF 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

) [pb] ! ! ! (Z’) * BR(Z’ "

• 3

10

• 2

10 95% CL limit

I

Z’

sec

Z’

N

Z’

#

Z’

$

Z’

%

Z’

SM

Z’

• 1

CDF 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. Motivation
• II. Strategy
• III. Results
• a. Heavy resonances (Z’)
• b. Heavy quarks (b’, t’)
• c. Simplified SUSY

4th generation

PDG says it’s ruled out to 6σ....

4th generation

[GeV]

d4

• m

u4

m

• 150
• 100
• 50

50 100 150 [GeV]

4 !

• m

l4

m

• 150
• 100
• 50

50 100 150 ) [%]

2

" # Prob(

• 1

10 1 10

projects.hepforge.org/opucem/

PDG says it’s ruled out to 6σ.... ..that’s true if the masses are degenerate

t’

Selection 1 lepton

pt>20 GeV

4 jets pt>20 GeV Missing transverse energy >20 GeV Sample 4.6/fb

28

UC Davis

t’

Limit mt’ > 335 GeV

29

UC Davis

b’

Selection 2 like-signed leptons

pt>20 GeV at least one isolated

2 jets pt>20 GeV

>=1 btags

Missing transverse energy >20 GeV Sample 2.7/fb

UCI Undergrad Matt Hickman

PRL 104 091801 (2010)

b’

Final selection 2 like-signed leptons 2 jets >=1 btags Missing transverse energy

PRL 104 091801 (2010)

mb’ > 338 GeV

b’ decays

If b’ -> Wt same-sign lepton selection: ~2% consider single-lepton mode

32

UCI undergrad Reza AmirArjomand

Signal (madgraph)

33

Number of jets 2 4 6 8 10 Fraction of Events 0.05 0.1 0.15 0.2 0.25

=300

b’

m =350

b’

m =400

b’

m

CDF Run II Preliminary

[GeV]

T

H

200 400 600 800 1000

Fraction of Events

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 jets 2 4 6 8 10 Fraction of Events 0.05 0.1 0.15 0.2 0.25

=300

b’

m =350

b’

m =400

b’

m

CDF Run II Preliminary

[GeV]

T

H

200 400 600 800 1000

Fraction of Events

0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 CDF Run II Preliminary

HT Scalar sum of transverse energy in the event Includes jets, lepton and missing transverse energy Captures soft recoil and unclustered jets

top quark pair background

tt + 0,1,2,3p p = udscb Madgraph+Pythia MLM matching

35

T

Jet-H 1000 2000 3000 Events

• 2

10

• 1

10 1 10

2

10 Backgrounds =350

b’

b’, m

CDF Run II Preliminary

Analysis technique

Events heavy and jetty Analysis variable

normalized to 5/fb

36

5j 6j 7j+

Data, >=1 b-tag

37

5j 6j 7j+

The numbers

38

The limits

39

Direct searches

mb’ > 372 GeV mt’ > 335 GeV replace

Direct searches

mb’ > 372 GeV

If BR(b’ →Wt)=100%

mt’ > 335 GeV

If 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 undergrad Matt Kelly UCI postdoc Christian 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’ + 50

PRL 2010, PRD 2011

Limits

V44 V34

290

300

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’

Selection 2 OS leptons

pt>20 GeV

2 jets pt>20 GeV Missing transverse energy >20 GeV Sample 35/pb

UCI grad student Michael Werth

topology

t

b W

t

b W

Boosted tops

topology

t

b W

t

b W

t’

b W

t’

b W

Boosted Ws!

Lepton-neutrino angles

Heavy t’ SM top

W

More W pT means smaller

• pening angle

Mass reconstruction

Assume lepton and neutrino are ~collinear

Data

No sign of heavy quarks...

Limit

Limit mt’ > 275 GeV

Limit

Limit mt’ > 275 GeV F i r s t L H C t ’ l i m i t s F i r s t t ’ d i l e p t

• n

s e a r c h

Dark Matter

Need long lived dark matter X

Dark Matter

Dark Matter X SM Particles

SM Charges Dark Charge

Need long lived dark matter X Give it some dark charge that is conserved (eg R-parity for susy LSP)

Dark Matter

Dark Matter X SM Particles

SM Charges Dark Charge

Need long lived dark matter X Give 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 X SM 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 gen

UCI grad student Kanishka Rao

Look for ttbar + invisible X T’ -> t+X stop -> t + LSP

Transverse mass

Limits

Outline

• I. Motivation
• II. Strategy
• III. Results
• a. Heavy resonances (Z’)
• b. Heavy quarks (b’, t’)
• c. Simplified SUSY

SUSY

Goal Set limits on SUSY-like processes in as general a fashion as possible Approach Use 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 postdoc Ning Zhou

SS SUSY simplified UCI postdoc

Ning Zhou

CDF Still producing world-class physics ATLAS Working well, much more to come