supersymmetry at the tevatron - slac · susy p x 1 1 p x 2 2 f (x ) f (x ) i j 1 2 s^ ij (x x ) 1 2...

Supersymmetryat theTevatron

Marc Hohlfeld

Rheinische Friedrich–Wilhelms–Universitat Bonnon behalf of the CDF and DØ experiments

– p. 1/3

Outline

• Introduction• Tevatron collider and detectors• Physics at the Tevatron• Search for Supersymmetry

N Direct searchesI Search for supersymmetric Higgs bosonsI Search for Charginos and NeutralinosI Search for Squarks and GluinosI Search for long lived particles

N Indirect searchesI Search for Bs → µµ

• Summary and outlookt

χ~b~

χ~g~

2

1+

0

~

SLAC Summer Institute, 08/02/2007 Marc Hohlfeld – p. 2/46

Particle ContentParticles in the Minimal Supersymmetric Model (MSSM)

R–parity = +1 R–parity = –1 R–parity = –1Particle Symbol Spin Particle Symbol Spin Particle Symbol Spin

Lepton ` 1

2Slepton ˜

L, ˜R 0

Neutrino ν 1

2Sneutrino ν 0

Quark q 1

2Squark qL, qR 0

Gluon g 1 Gluino g 1

2

Photon γ 1 Photino γ 1

29

>

>

>

>

=

>

>

>

>

;

Z Boson Z 1 Zino Z 1

2

W Boson W± 1 Wino W± 1

24 Neutralinos χ0

i1

2

Higgs H0, H± 0 Higgsino H01, H+

21

22 Charginos χ±

i1

2

h0, A0 0 H−

1, H0

21

2

• Assumptions in this talkN Consider mSUGRA model

I Relevant parameters: tan β, m0, m1/2, A0, sign(µ)N R–parity is conserved ⇒ LSP (Neutralino) is stable


Tevatron Parameters

• pp collisions at center of mass energy of √s = 1.96 TeV

Run I Run IIa Run IIb√

s (TeV) 1.8 1.96 1.96Bunches 6×6 36×36 36×36Bunch spacing 3500 396 396(ns)Luminosity 1.6 · 1030 9 · 1031 3 · 1032

(cm−2s−1)


Tevatron Performance

Run IIa Run IIb

Run IIa: 1.5 fb delivered

Run IIb: 1.6 fb delivered 1.3 fb recorded

1.4 fb recorded−1

−1−1

−1

• Tevatron coming close to design luminosity for Run IIbN Improved antiproton stacking rateN Peak luminosity ∼ 300 · 1030 cm−2s−1

• Integrated luminosity of 7–8 fb−1 by end of 2009 realistic projection


The Detectors

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Central Outer Tracker

Calorimeter

Silicon Strip Detector

Solenoid

Muon System

• Two multipurpose detectorsN Identification of electrons, muons,

taus, jets, missing transverse energy• Fast readout electronics

N Bunch spacing 396 ns• Dedicated trigger systems

N Rate reduction from 2.5MHz to 50Hz

• CDF detectorN Large tracking volume

• DØ detectorN Large acceptance for electrons

and muons

PP

NORTH SOUTH

H−DisksF−DisksSi−Barrels

Superconducting Coil CPSCFT

FPS

Toroid Solenoid

Central PreshowerTracker (CFT)Central Fiber

Detector (CPD)

Scintillators

Tubes (MDT)Mini Drift

Calorimeter

Tracker (SMT)Silicon Micro

Forward Preshower Detector (FPD)

Tubes (PDT)Proportional Drift


The Detectors (cont’d)


Physics at the Tevatron

• Physics at the Tevatron is characterized byN High center–of–mass energy of the collider

I Production of massive particles possibleI top–quark, Higgs, SUSY particles,

heavy gauge boson,...N Particles are produced in strong interaction

I Huge cross section for jet productionI Need large reduction to see signals

N 7 interactions/crossing at 3 · 1032cm−2s−1

0.1 1 1010 −7

10 −5

10 −3

10 −1

10 1

10 3

10 5

10 7

10 109 9

10 −7

10 −5

10 −3

10 −1

10 1

10 3

10

10 5

7

σjet(E Tjet > √s/4)

LHCTevatron

σt

σZ

σjet(E Tjet > 100 GeV)

σHiggs (M H = 150 GeV)

σW


σb

σtot

σ (

nb)

√s (TeV)

Proton−(Anti−)Proton Wirkungsquerschnitte

SUSY

p x1 1

p x2 2

f (x )

f (x )

i

j

1

2

σij (x x )21

Hadr

onis

atio

n

^

p

p

1

2

Spectators/ULE

hadronshard

interaction showerpartonincoming

N Final states are complicatedI Fragmentation of spectatorsI Additional jets due to gluon radiation


SUSY at the Tevatron

• There are three major areas to search for Supersymmetry at the TevatronN Search for supersymmetric Higgs bosons

I Search for Higgs bosons in τ final statesI Higgs bosons searches using b–jets

N Direct searches for other SUSY particlesI Squarks and GluinosI Charginos and NeutralinosI Long lived particles

N Indirect searches• Only a few selected topics will be covered in this talk• For a comprehensive overview please refer toCDF http://www-cdf.fnal.gov/physics/physics.htmlDØ http://www-d0.fnal.gov/Run2Physics/WWW/results.htm


http://www-cdf.fnal.gov/physics/physics.html

http://www-d0.fnal.gov/Run2Physics/WWW/results.htm

Search for SUSY Higgs Bosons


Search for SUSY Higgs Bosons• 5 Higgs bosons are predicted in SUSY models

N MSSM Higgs sector specified by tanβ, mA

• Neutral Higgs bosons h/H/A can be produced via gluonfusion or in association with jetsN Coupling increases with tan2 β ⇒ Large cross section

• At high tan β the main decay modes areN h/H/A→bb: 90% h/H/A→ ττ : 10%

τ τhh

τ τµ h

τ τhe

τ τµ e

τ τe e

τ τ µ µ

• Focus on ττ final stateN Golden channels are τhτe and τhτµ

I Large branching fraction, moderate backgroundN Other channels are less important

I Fully leptonic channels: small branching fractionI Fully hadronic mode: huge multijet background


Search for SUSY Higgs Bosons (2)• Major backgrounds are Z/γ∗ → ττ and multijet production

N Require isolated lepton and isolated τ to reduce QCD contributionN Further reduce QCD by requiring large HT =

∑

pT

N Veto on events where E/T is aligned with visible τ decay products tosuppress W+jet events

• Finally reconstruct visible massN Mvis =

√

(E` + Eτ + E/T)2 − (p`x + pτ

x + E/xT )2 − (p`

y + pτy + E/

yT )2 − (p`

z + pτz )2

Visible Mass (GeV)0 50 100 150 200 250

Even

ts

1

10

210

0 50 100 150 200 250

1

10

210

ττ→M=160hττ→Z

QCDνµ→W

µµ→Zντ→W

ν lνl→WWtt

-1 Preliminary, 1.0 fb∅D

µe channel


Search for SUSY Higgs Bosons (3)

mvis (GeV)

-

• CDF (3 channels)N 2σ excess in τhτe and τhτµ channels

I mA ≈ 150 GeV, tanβ ≈ 50N No excess in τeτµ channel

• DØ (1 channel)N No excess in τhτµ channelN Expect results in τhτe and τeτµ channels

later this summer

100 150 200 250

10

1

100

0.1

mφ (GeV)

σ(pp

→φX

) x BR

(φ→

ττ)

(pb

)

95% CL upper limits

CDF Run II 1 fb-1

MSSM Higgs→ττ Search

Preliminary

Observed

Expected

1σ band

2σ band


Limits• Although there is excess seen by CDF, no evidence for Higgs production (yet)

N Set limits in the tan β–mA–plane

mA

(GeV/c2)

80

tan

β

100 120 140 160 180 2000

20

40

60

80

100

no mixing

LEP 2mh

max

˜–µ = -200 GeV, M

2 = 200 GeV, m

g = 0.8 M

SUSY

MSUSY

= 1 TeV, Xt = √6 M

SUSY (m

hmax), X

t = 0 (no-mixing)

CDFµ<0

expected

observed

no mixing

CDF Run II 1 fb-1

MSSM φ→ττ Search

Preliminary

mhmax

• What to expect in the futureN More data, more channels, combination with bh → bbb result


Search for Charginos and Neutralinos


Search for Charginos and Neutralinos• Associated production of Charginos and Neutralinos

N Via W boson or Squark exchange• Decay of Chargino

N W bosons and lightest NeutralinoN Slepton and neutrino

• Decay of NeutralinoN Z bosons and lightest NeutralinoN Slepton and lepton

qqqq χ 0

1~χ 0

1~

qq

~W +

Z

W+

l

l+

−

l+

ν

l+

l+

ν

χ~ 01

~ 0χ 1χ~+

χ02

~χ0

2~

χ 01

~

χ+~ χ 01

~

~~l+l+

q

+l

• Final state consists of three charged leptons, two Neutralinos and a neutrino

(GeV)Tp0 10 20 30 40 50 60 70 80 90 100

arbi

trary

uni

ts

0

200

400

600

800

1000

1200

1400

1600

1Tp2Tp3Tp

• Trilepton channel is the golden mode for the search ofCharginos and NeutralinosN Signature: three charged leptons plus

missing transverse energy• Challenges

N Leptons have low transverse momentaN Small cross sections: σ×BR < 0.5 pb


Backgrounds and Selection• Main background is QCD multijet production

N Very large cross section• Require two isolated leptons

N Main contributions from Z/γ production

)2) (GeV/c2,l1Invariant mass (l20 40 60 80 100 120 140 160 180

No. o

f eve

nts

-110

1

10

210

310

410

)2) (GeV/c2,l1Invariant mass (l20 40 60 80 100 120 140 160 180

No. o

f eve

nts

-110

1

10

210

310

410

ee+l+X→ ±1χ0

2χSearch for DataFake leptonDrell-Yantt

DibosonsγZ + γW +

SUSY

CDF Run II Preliminary-1 L dt ~ 1 fb∫

0.1 1 1010 −7

10 −5

10 −3

10 −1

10 1

10 3

10 5

10 7

10 109 9

10 −7

10 −5

10 −3

10 −1

10 1

10 3

10

10 5

7


LHCTevatron

σt

σZ



σW


σb

σtot

σ (

nb)

√s (TeV)


SUSY




N Main contributions from Z/γ production• Further possibilities to suppress background

N Require a third lepton or trackN Leptons must have same chargeN Diboson production main contributor

Trans. Mass (3rd Track,MET) (GeV)0 20 40 60 80 100 120 140

-210

-110

1

10D0 RunII Preliminary,1.1fb-1 data

ττ →Z QCD fakes W W

ν l→W µ e→tt

, eeµµ →Z WZ/ZZ SUSY point (131.232)

D0 RunII Preliminary,1.1fb-1

0.1 1 1010 −7

10 −5

10 −3

10 −1

10 1

10 3

10 5

10 7

10 109 9

10 −7

10 −5

10 −3

10 −1

10 1

10 3

10

10 5

7


LHCTevatron

σt

σZ



σW


σb

σtot

σ (

nb)

√s (TeV)


SUSY




N Main contributions from Z/γ production• Further possibilities to suppress background

N Require a third lepton or trackN Leptons must have same chargeN Diboson production main contributor

• Three different selection criteriaN Three identified leptonsN Two leptons plus additional track

I Higher efficiency, but slightlymore background

N Likesign selectionI Sensitive in regions with low pT third

lepton0.1 1 10

10 −7

10 −5

10 −3

10 −1

10 1

10 3

10 5

10 7

10 109 9

10 −7

10 −5

10 −3

10 −1

10 1

10 3

10

10 5

7


LHCTevatron

σt

σZ



σW


σb

σtot

σ (

nb)

√s (TeV)


SUSY


Selection with Two Leptons

• PreselectionN Two good reconstructed leptons

• Anti–Z/γ∗ → ee, Z/γ∗ → µµ cutsN Small invariant massN Not back–to–back leptons

χ

χν

Lepton 1

Lepton 2

Lepton 3

Lepton 1

Lepton 2Jet 1

missing ET

missing ET

• Significant missing transverse energy

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

-310

-210

-110

1

10

210

310

410

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5

-310

-210

-110

1

10

210

310

410

Data mumu→Z

QCD tautau→Z mu nu →W

mumu→Y(1s) W gammastarZZ 4l tt 2l 2b WW 2l + 2nuWZ 3l + nuZ bbW bbSUSY

Delta phi electrons, Stack_05

)µ, µ (φ ∆

-1DØ Preliminary, 1fb

(GeV)TMissing E0 20 40 60 80 100 120

No. o

f eve

nts

1

10

210

(GeV)TMissing E0 20 40 60 80 100 120

No. o

f eve

nts

1

10

210+l+Xµ e→ ±

1χ02χSearch for Data

Fake leptonDrell-Yan

tt Dibosons

γZ + γW +

SUSY

CDF Run II Preliminary-1 L dt ~ 1 fb∫


Cuts using E/T

• E/T related cutsN Cut on E/T itselfN Transverse mass cut: mT =

√

pT · E/T · (1 − cos∆Φ(e, E/T))

I Rejects events with mismeasured lepton energies

BackgroundSignal

true pT

true pT

reco pT

missing ET

T reco psmall angle

reco pT

T reco p true pT

true pT

missing ET

large angle

0 10 20 30 40 50 60 70 80 90 100

-310

-210

-110

1

10

210

310

410

0 10 20 30 40 50 60 70 80 90 100

-310

-210

-110

1

10

210

310

410

Data ee→Z tautau→Z e nu →W

ee→Y tt 2l 2b WW 2l + 2nuWZ 3l + nuZZ 4l or 2l + 2nuQCDSUSY



) [GeV]2

, Mtr1

min(MtrEv

ents

/ 1

GeV -1DØ RunII Preliminary 1.1 fb

N Significance of E/T: Sig(E/T) = E/Tr

P

jetsσ2(Ejet

T ||E/T)

I Only defined for events with jetsI Rejects events with mismeasured jet energies

Lepton 1

Lepton 2Jet 1

missing ET0 20 40 60 80 100 120 140 160 180 200

-310

-210

-110

1

10

210

310

410

0 20 40 60 80 100 120 140 160 180 200

-310

-210

-110

1

10

210

310

410



)TESig(

Even

ts

-1DØ RunII Preliminary 1.1 fb


Cuts using E/T

• E/T related cutsN Cut on E/T itself

N Transverse mass cut: mT =√

pT · E/T · (1 − cos∆Φ(e, E/T))

I Rejects events with mismeasured lepton energies

BackgroundSignal

true pT

true pT

reco pT

missing ET

T reco psmall angle

reco pT

T reco p true pT

true pT

missing ET

large angle

0 10 20 30 40 50 60 70 80 90 100

-310

-210

-110

1

10

210

310

410

0 10 20 30 40 50 60 70 80 90 100

-310

-210

-110

1

10

210

310

410





) [GeV]2

, Mtr1

min(MtrEv

ents

/ 1

GeV -1DØ RunII Preliminary 1.1 fb

N Significance of E/T: Sig(E/T) = E/Tr

P

jetsσ2(Ejet

T ||E/T)

I Only defined for events with jetsI Rejects events with mismeasured jet energies

Lepton 1

Lepton 2Jet 1

missing ET0 20 40 60 80 100 120 140 160 180 200

-310

-210

-110

1

10

210

310

410

0 20 40 60 80 100 120 140 160 180 200

-310

-210

-110

1

10

210

310

410



)TESig(

Even

ts

-1DØ RunII Preliminary 1.1 fb


Third Track Selection• Select high quality track to account for the third lepton

N Track must be isolated in tracker and calorimeterI Efficient for electrons, muons and taus, suppresses tracks in jets

N Use hollow cone for isolationI Also efficient for (3 prong) tau decays

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(1 prong)TauElectron Muon Tau

(3 prong)

Signal Background

Jet

0 10 20 30 40 50 60 70 80 90 100

-310

-210

-110

1

10

210

0 10 20 30 40 50 60 70 80 90 100

-310

-210

-110

1

10

210



Transverse momentum [GeV]

Even

ts /

1 G

eV -1DØ RunII Preliminary 1.1 fb


Result• No evidence for Charginos and Neutralinos found

N Set limits on the production cross section times branching ratioN Translate these limits in mass limits

Chargino Mass (GeV)100 110 120 130 140 150 160

BR(

3l) (

pb)

×) 20 χ∼ 1± χ∼ (σ

0

0.1

0.2

0.3

0.4

0.5

)20χ∼)>M(l~); M(

10χ∼2M(≈)

20χ∼M(≈)

1±χ∼M(

>0, no slepton mixingµ=3, βtan

-1DØ Run II Preliminary, 0.9-1.7 fb

LEP

3l-maxheavy-squarks

0large-m

Observed LimitExpected Limit

Chargino Mass (GeV)100 110 120 130 140 150 160

BR(

3l) (

pb)

×) 20 χ∼ 1± χ∼ (σ

0

0.1

0.2

0.3

0.4

0.5

• Cross section limit: σ×BR∼0.06 pb• 3`–max scenario (m ˜

R& mχ±

1

)N mχ±

1

> 145 GeV

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

100 110 120 130 140 150 160Chargino Mass (GeV/c2)

σ(χ∼

0 2χ∼± 1)×

BR(3

lept

ons)

(pb)

σNLO×BRσNLO×BR Uncertainty95% CL Upper Limit: observed95% CL Upper Limit: expectedExpected Limit ± 2σExpected Limit ± 1σ

CDF Run II Preliminary: 700-1000 pb-1MSSM: tanβ=3, µ>0, M(χ

∼02)∼M(χ

∼±1)∼2M(χ

∼01); no slepton mixing

Excludedby LEP

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

• Cross section limit: σ×BR∼0.2 pb• mSUGRA model without ˜–mixing

N mχ±

1

> 130 GeV


Search for Squarks and Gluinos


Search for Squarks and Gluinos

• Squarks and Gluinos can be producedvia strong interactionN Production depends on the masses

of the Squarks and GluinosI Either gg, qg or qq

N Decays of Squarks and GluinosI Squarks: q → qχ0

I Gluinos: g → qqχ0

⇒ Three different analysis scenarios1 qq: 2 jets + E/T (Dijet analysis)2 qg,qq: 3 jets + E/T (3–jet analysis)3 gg: 4 jets + E/T (Gluino analysis)

m( ) m( )

g~m( )

q~m

( ) ~>>q~ gm( ) m( )

=m( )

q~

g~

m( )

m( )>> q~g~m( )

~~

Gluino Mass

Squa

rk M

ass

~~

qg production dominantFinal state: 3 jets + E

~qq production dominantFinal state: 2 jets + E~

~ ~g q

gg production dominantFinal state: 4 jets + E~ ~

T

T

T


Squark and Gluino Selection• Common selection for all three analyses

N 2 acoplanar jets and large E/TI 1 or 2 additional jets (3–jet, Gluino analysis)

N Reject events with electrons or muonsI Suppress W and Z events

N Veto on events where E/T is aligned with jetsI Reject events with mismeasured jets

,any jet) (degrees)TE(min

φ∆0 20 40 60 80 100 120 140 160 180

Even

ts /

5

0

50

100

150

200

250

300

0 20 40 60 80 100 120 140 160 1800

50

100

150

200

250

300

DØ PreliminaryData

+ jetsν l→W + jetsνν →Z

ttWW,WZ,ZZ

+ jets-l+ l→Zsingle-tSignal

Neutralino

Missing E

Neutralino

T

Jet Jet

⇐ Signal configuration

QCD background ⇒

Jet 1

Jet 2missing ET

reco jet pT

reco jet pT

true jet pT

true jet pT

• At the end cuts on E/T and HT are optimized for every selection

(GeV)TE0 50 100 150 200 250 300 350 400 450 500

Even

ts /

20

1

10

210

310

410

0 50 100 150 200 250 300 350 400 450 500

1

10

210

310

410DØ Preliminary

Data + jetsν l→W + jetsνν →Z

ttWW,WZ,ZZ

+ jets-l+ l→Zsingle-tSignal ⇐ E/T distribution

HT distribution ⇒

[GeV]T H200 300 400 500 600 700 800 900

Eve

nts/

40 G

eV

-110

1

10

210

310

[GeV]T H200 300 400 500 600 700 800 900

Eve

nts/

40 G

eV

-110

1

10

210

310)-1Data (Lum = 1.1 fb

QCD DiBoson

)+jets ν W(e )+jets ν µ W()+jets ν τ W(

Z(e e)+jets )+jets µ µ Z(

)+jets τ τ Z()+jets ν ν Z(

t t

CDF Run II Preliminary

• Results from DØ based on 1 fb−1 of data

Selection Signal Efficiency (%) Data BackgroundDijet 7.05 ± 0.39+0.96

−0.88 5 7.47 ± 1.06+1.32−1.02

3–Jet 6.66 ± 0.37+1.11−1.01 6 6.10 ± 0.37+1.26

−1.16

Gluino 5.74 ± 0.35+0.81−0.72 34 33.35 ± 0.81+5.56

−4.92

• No evidence found for production of Squarks and Gluinos at Tevatron


Event DisplaysHighest E/T events

Dijet analysis• E/T = 368 GeV• HT = 489 GeV• p

jet1

T = 282 GeV, pjet

2

T = 174 GeVp

jet3

T = 33 GeV

Gluino analysis• E/T = 321 GeV• HT = 464 GeV• p

jet1

T = 254 GeV, pjet

2

T = 77 GeV,p

jet3

T = 67 GeV, pjet

4

T = 66 GeV


Results• The analyses are optimized for three benchmark scenarios

N Vary m0 and m1/2, other parameters constant: A0 = 0, µ < 0 and tan β = 3/5

Gluino Mass (GeV)0 100 200 300 400 500 600

Squa

rk M

ass

(GeV

)

0

100

200

300

400

500

600-1DØ Preliminary, 0.96 fb

<0µ=0, 0

=3, Aβtan

UA1

UA2

LEP

CDF

IB

DØ IA

DØ IB

no mSUGRA

solution

CDF

II

)2 (GeV/cg~M0 100 200 300 400 500 600

)2 (G

eV/c

q~M

0

100

200

300

400

500

600observed 95% C.L.

σobserved +/-1obs. ISR/FSR syst. incl.expected 95% C.L.

no mSUGRAsolution

)10

χ∼) < m(q~m(LEP 1 + 2

UA1

UA2

FNAL Run I

g~

= Mq~M

CDF Run II Preliminary -1L=1.1 fb

3-jets inclusive<0µ=5, β=0, tan0A

)2 (GeV/cg~M0 100 200 300 400 500 600

)2 (G

eV/c

q~M

0

100

200

300

400

500

600

• Mass limitsN Squarks: 391 (375) GeV Gluinos: 309 (289) GeV


Search for long lived particles


Search for CHAMPS• Search for long lived Charged Massive Particles

N Particles do not decay inside the detectorN Highly ionizing and penetrating

• Signature in the detector: “slow muon”N Particle penetrates cal and muon systemN Use time–of–flight system to measure β

• Signal expected at high massN Background sits at low mass

)2 (GeV/cTOF

βMass from track momentum and 0 50 100 150 200 250 300

Even

ts /

10 G

eV

-110

1

10

210

)-1CDF Run II Preliminary (1.0 fb

> 40 GeVT

, pµCentral

Background Prediction Stop2220 GeV/c

)2Stop Mass (GeV/c100 120 140 160 180 200 220 240 260

Cros

s se

ctio

n (p

b)

-210

-110

1

10 Stop Production cross section (NLO)µCross section limit from central

-1 = 1.03 fbL dt ∫

CDF Run II Preliminary • Main background componentsN Cosmic muons and instrumental

background• Interpreted in SUSY models with one

compactified extra dimensionN In these models Stop is the LSP

• Mass limit: mt > 250 GeV


Search for Long lived Gluinos• Long lived Gluinos are predicted in several models

N For example split SUSY• Gluinos can stop inside the detector

N Can decay at random times ⇒ Not related to any beam crossingN Decay can also occur if no beam is in the machine

• Very hard to model trigger for these events• Need a good model for the alive time of the

detector

Gluino Mass (GeV)150 200 250 300 350 400 450 500 550 600

Cros

s Se

ctio

n Li

mit

(pb)

-110

1

-1, L=410 pbOD

100 hours18 hours<3 hours

• No evidence for stopped Gluinos


Indirect searches


Search for Bs → µµ

• New physics can also be observed indirectly• The decay Bs → µµ is a very good candidate

N Decay is a flavor changing neutral currentI In the SM it is forbidden at tree level

⇒ Small branching fraction:BR(Bs → µµ) = (3.4 ± 0.4) · 10−9

N Enhancement in SUSY models: ∼ (tan β)6

−W −µ

+µ+W

s

b

t υ l

−µ

+µ

dHs

b

• Blind analysis ⇒ Predict events in signal region from sidebandsN Good agreement between number of events predicted and observedN No observation ⇒ Upper limits on the branching fraction

]2) [GeV/c-µ +µInvariant mass (4.6 4.8 5 5.2 5.4 5.6 5.8 6 6.2 6.4

)2Ev

ents/

5 (M

eV/c

0

0.5

1

1.5

2

2.5Signal regionSideband 1

DØ Run IIb PreliminarySideband 2

• Current limitsN DØ (2 fb−1): BR(Bs → µµ) < 9.3 · 10−8

N CDF (0.78 fb−1): BR(Bs → µµ) < 1.0 · 10−7


Conclusion• Summary

N Tevatron, CDF and DØ are performing wellI Already collected more than 2.7 fb−1 of dataI Nearly factor three more than the data used in the results presented here

N SUSY searches probing new regions in phase spaceI New mass limits beyond LEP2 limits

• Tevatron will further probe Supersymmetry in so far uncovered territory

O. Buchmueller et al.,arXiv:0707.3447v1


– p. 2/2

– p. 3/2

BACKUP SLIDES


Search for Stop Quarks• Due to mixing in third generation, Stop can be light

N Can be pair produced at the Tevatron• If Stop is light enough it can only decay into cχ0

1

N The decays tχ01 and bχ±

1 are forbidden• Major background contributions are

N W+jets, Z+jets and multijet production• Selection strategy

N Select events with acoplanar dijetsN Reject events with isolated electrons, muons

or tracksN Require large E/T and H/T

N Apply heavy flavor tagging to reduce lightjet contributions from background

• Optimize selection for different mass points


Search for Stop Quarks (2)• Main background after final selection

N W(→ `ν) = jets and Z(→ νν) + jetsN Background varies between 57 and 82 events depending on Stop mass

• Signal efficienciesN Range from 0.1% to 5% depending on Stop and Neutralinos mass

• Data is in agreement with the SM expectation

• Mass limitsN Stop: mt > 160 GeVN Neutralino: mχ0

1> 75 GeV


Search for GMSB

• In Gauge Mediated SUSY Breaking (GMSB) models the Gravitino G is the LSPN If the Chargino χ0

1 is the NLSP it decays to Gravitinos: χ01 → γG

N Final state consists of two photons and E/T due to escaping Gravitinos• Search for inclusive γγ+E/T events with 1.1 fb−1 of data

(GeV)T

Missing E0 20 40 60 80 100 120 140 160 180 200

N / 3

GeV

-110

1

10

210

310 dataγγ

γγW/Z+electron mis-IDjet mis-ID

=75 TeVΛSM + signal =90 TeVΛSM + signal

(GeV)T

Missing E0 20 40 60 80 100 120 140 160 180 200

N / 3

GeV

-110

1

10

210

310 -1 Preliminary 1.1 fb∅D• Major background components

N Events with true E/T

I W+jets/γ, tt

N Events with instrumental E/T

I Multijets and direct γγproduction, Z → ee

• Diphoton selection yields 2341 events


Search for GMSB (2)• Search for the signal in the high E/T region (for different energy scales Λ)

E/T Background Data Signal(GeV) true E/T fake E/T Total Λ = 75 TeV Λ = 90 TeV> 30 1.16 ± 0.14 9.62 ± 1.12 10.8 ± 1.1 16 28.3 ± 1.0 8.7 ± 0.3> 60 0.19 ± 0.07 1.44 ± 0.43 1.6 ± 0.4 3 18.1 ± 0.8 6.4 ± 0.3

(TeV)Λ70 75 80 85 90 95 100 105 110

(fb)

σ

10

210

[GeV]10χm

100 120 140

[GeV]1+χm

180 200 220 240 260

-1 Preliminary 1.1 fb∅D LO cross-sectionNLO cross-sectionexpected limit

observed limit • No evidence for a signal• Energy scale and mass limits

N Λ > 92 TeVN mχ±

1

> 231 GeV, mχ0

1> 126 GeV


Search for GMSB (3)• Search for long lived Neutralinos

N In GMSB models pair production of Gauginos is dominantN Gauginos decay into the lightest Neutralino

I Final states consists of a delayed photon, jets and E/T

• Main selection criteriaN Select events with time delayed photonN Require large E/T

• Mass limit (depending on lifetime)N mχ0

1> 101 GeV for τ = 5 ns


Search for Stops in the Dilepton Channel• Search for scalar top quarks in final states with two leptons and two b–quarks

N t decays dominantly into b`ν if t → bχ±1 and t → bχ0

1 are forbidden• Main selection criteria

N Two isolated leptonsN At least two jets, highest pT jet must be tagged as b–jet (only µµ channel)N Significant E/T

N Other kinematic variables: invariant mass, scalar sum of all pT


Search for Stops in the Dilepton Channel (2)

Background Data Signaltt Diboson Total Point A Point B

ee 7.4 20.2 31.7 ± 2.7 34 26.0 ± 1.5 17.3 ± 0.6eµ 2.3 0 2.9 ± 0.4 1 3.1 ± 0.2 3.3 ± 0.4

• Good agreement of data and SM prediction

• Mass limits in mt–mν planeN Largest mt limit: mt > 186 GeV

(for mν = 71 GeV)N Largest mν limit: mν > 107 GeV

(for mt = 145 GeV)


Search for Sbottom Quarks• For high tan β the b–mass eigenstates have large separation

N Sbottom quarks might be light enough to be pair produced at the TevatronN Assume 100% branching fraction of b into bχ0

1

• Final state consists of two b–jets and E/T

• Event selectionN At least two high pT jets, one jet must be tagged as b–jetN Require significant E/TN Veto on isolated leptons

(GeV)T1st Leading Jet E0 50 100 150 200 250 300 350 400

Even

ts/1

0 G

eV

0

2

4

6

8

10

12

14

16

18

20

22

(GeV)T1st Leading Jet E0 50 100 150 200 250 300 350 400

Even

ts/1

0 G

eV

0

2

4

6

8

10

12

14

16

18

20

22

DataMis-TagQCD (HF)EWK+TopSignal

,2)=120 GeV/c1t~(M(

)2)=50 GeV/c10

χ∼M(

-1CDF Run II Preliminary, 295 pb

(GeV)TMissing E0 50 100 150 200 250

Even

ts/5

GeV

0

1

2

3

4

5

6

(GeV)TMissing E0 50 100 150 200 250

Even

ts/5

GeV

0

1

2

3

4

5

6

DataMis-TagQCD (HF)EWK+TopSignal

,2)=160 GeV/c1b~(M()2)=80 GeV/c1

0χ∼M(

-1CDF Run II Preliminary, 295 pb


Search for Sbottom Quarks (2)• Data is well described from SM prediction

Sbottom Mass (GeV)0 50 100 150 200

Sbottom Mass (GeV)0 50 100 150 200

Neut

ralin

o M

ass

(GeV

)

0

50

100expectedobserved

CDF Run I-188 pb

DØ Run II-1L = 310 pb

LEP=208 GeVs

)10χ

) = M

(b) +

M(

b~M(

)2) (GeV/c1b~M(0 20 40 60 80 100 120 140 160 180 200 220

)2) (

GeV

/c10 χ∼

M(

0

20

40

60

80

100

120ObservedExpected limit

Run 2∅DCDF Run 1LEP )10

χ∼

)=M(

b)+M

(

1b~M(

)-1CDF Run II Preliminary (295 pb

CDF Run2 : Theoretical uncertaintyincl. PDF, and renormalizationand factorization scale

Run2 : Theoretical uncertainty∅Dincl. renormalization andfactorization scale

• Mass limitsN DØ (310 pb−1): mb > 222 GeVN CDF (290 pb−1): mb > 195 GeV


Search for Stop Quarks• Search for scalar top admixture in tt events in the lepton+jets channel

N Stop quarks are pair producedN Decay channels

I t1 → bχ+1 → bWχ0

1

I t1 → bχ+1 → cχ0

1

N σ(t1t1) ≈ 0.1×σ(tt) for masses of 175 GeV• Start from a selection that is similar

to tt selectionN Main backgrounds for tt measure–

ments are W+jet and multijet eventsN tt events are of course the major

(irreducible) background for stopsearchI Use Likelihood to discriminate

top decays


Search for Stop Quarks (2)• Combine up to five variables in the Likelihood

mass[GeV]0 50 100 150 200 250 300

# of

ent

ries

00.020.040.060.08

0.10.120.140.160.18

0.2Hitfit reconstructed top 1 mass

StopTopW+jets

DØ PreliminaryHitfit reconstructed top 1 mass

top mass [GeV]0 50 100 150 200 250 300

# of

ent

ries

0

5

10

15

20

25

Hitfit reconstructed top 1 mass

top mass [GeV]0 50 100 150 200 250 300

# of

ent

ries

0

5

10

15

20

25

datastop x10(175/135)ttbarWbbWccWlpZ+jetssingletopdibosonQCD

-1871 pb

PreliminaryOD

Hitfit reconstructed top 1 mass

Likelihood0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

# of

ent

ries

0

5

10

15

20

25

30

35

40

Likelihood for stop 175/135

Likelihood0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

# of

ent

ries

0

5

10

15

20

25

30

35

40

datastop x10(175/135)ttbarWbbWccWlpZ+jetssingletopdibosonQCD

-1871 pb

PreliminaryOD

Likelihood for stop 175/135

• Events observed consistent with SM prediction• No evidence for stop quark admixture• Upper limits on stop quark production

N σ(t1t1) < 5.7–12.8 pb (at 95% CL)N Factor 7–12 above the MSSM prediction


supersymmetry at the tevatron - slac · susy p x 1 1 p x 2 2 f (x ) f (x ) i j 1 2 s^ ij (x x ) 1 2...

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