Search for Charginos and Neutralinos with the DØ Detectorsusy06.physics.uci.edu/talks/1/hohlfeld.pdfSearch for Charginos and Neutralinos with the DØ Detector Marc Hohlfeld Laboratoire

Search for Charginos andNeutralinos with the DØ Detector

Marc Hohlfeld

Laboratoire de l’Accelerateur Lineaire, Orsayon behalf of the DØ Collaboration

SUSY 2006, 06/13/2006

SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 1/17

Outline

• Introduction

• Tevatron collider and DØ detector

• Signal and background

• Selection criteria

• Results

• Summary and outlook


Introduction

• mSUGRA: five parameters ⇒ m0, m1/2, tan β, µ, A0

• R–parity: R = (−1)3(B−L)+2S ⇒ Conserved ⇒ LSP (neutralino) is stable

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

Lepton ` 12

Slepton ˜L, ˜

R 0

Neutrino ν 12

Sneutrino ν 0

Quark q 12

Squark qL, qR 0

Gluon g 1 Gluino g 12

Photon γ 1 Photino γ 12

9

>

>

>

>

>

>

>

=

>

>

>

>

>

>

>

;

Z Boson Z 1 Zino Z 12

W Boson W± 1 Wino W± 12

Neutralino χ0i

12

Higgs H0, H± 0 Higgsino H01, H+

212

Chargino χ±

j12

h0, A0 0 H−

1 , H02

12

• LEP limit for the chargino mass: mχ±

1

> 103.5 GeV


Tevatron and Data Taking

• pp collisions at center of mass energy of√

s = 1.96 TeV

PRL 95, 151805 (2005)

Update (2006)

• First DØ Run II Trilepton paper published in 2005 (∫

Ldt ∼ 300 pb−1)

• Now update with 3–4 times more data (∫

Ldt ∼ 1 fb−1)


The DØ Detector

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

• Detector comprises severalsubdetectores

• Vertex– and tracking detector

N Detection of verticesN Measurement of the momentum

of charged particlesN Measurement of the charge

• Calorimeter

N Detection of electrons, photonsand jets

N Measurement of the energyN Indirect detection of neutrinos

using missing transverse energy

• Muon spectrometer

N Detection of muonsN Standalone measurement of

muon momentum


The DØ Detector

PP

NORTH SOUTH



FPS

Toroid Solenoid


Detector (CPD)

Scintillators


Calorimeter








• Calorimeter






muon momentum


The DØ Detector

PP

NORTH SOUTH



FPS

Toroid Solenoid


Detector (CPD)

Scintillators


Calorimeter








• Calorimeter






muon momentum


The DØ Detector

PP

NORTH SOUTH



FPS

Toroid Solenoid


Detector (CPD)

Scintillators


Calorimeter








• Calorimeter






muon momentum


Search for Charginos and Neutralinos

• Associated production of charginos andneutralinosN s–channel: via W bosonN t–channel: squark exchangeN Destructive interference

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

• Decay of charginoN W bosons and lightest neutralino, W decays into lepton and neutrinoN Slepton and lepton, slepton decays into lightest neutralino and lepton

• Decay of neutralinoN Z bosons and lightest neutralino, Z decays into two leptonsN Slepton and neutrino, slepton decays into lightest neutralino and lepton

• Final state consists ofN Three charged leptonsN Two neutralinos (LSP)N One neutrino


Search for Charginos and Neutralinos (2)

• Trilepton channel is the golden mode forchargino/neutralino searchN Signature: three charged leptons plus

missing transverse energy• Challenges

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

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

arb

itra

ry u

nit

s

0

200

400

600

800

1000

1200

1400

1600

1Tp2Tp3Tp

pp

−

−

− ( s = 2 TeV)

10−3

10−2

10−1

1

100 150 200 250m(χ1

±,χ2o) (GeV)

: χ1o

χ2oχ2

o

χ1±χ2

o

χ1+χ1

−

σ

σ

(pp

(pp

χ

χ

1

1

o

o

χ

χ

2

2

o

o

,

,

χ

χ

2

2

o

o

χ

χ

2

2

o

o

,

,

χ

χ

1

1

±

±

χ

χ

2

2

o

o

,

,

χ

χ

1

1

+

+

χ

χ

11

−

−

) ) (pb)(pb)

53 80 105 129

10 • Four different analyses

N Update summer 2006I ee+track:

∫

Ldt ∼ 1.1 fb−1

I like-sign µµ:∫

Ldt ∼ 0.9 fb−1

N PRL 2005I eµ+track:

∫

Ldt ∼ 320 pb−1

I µµ+track:∫

Ldt ∼ 300 pb−1


Signal Monte Carlo

• Three reference points (Les Houches Accord)

Heavy Medium Light

m0 (GeV) 121 98 88m1/2 (GeV) 221 192 182tan β 3 3 3µ > 0 > 0 > 0A0 0 0 0

mχ±

1

(Gev) 150 125 115mχ0

2(GeV) 152 127 118

mχ0

1(GeV) 82 69 63

m˜R

(GeV) 153 129 119

σ×BR (pb) 0.058 0.14 0.22

• Mass of sleptons just above the neutralino masses: m ˜R

& mχ0

2


Backgrounds

• Background components

N Vector boson pair productionI WW =⇒ 2 leptons+E/TI WZ =⇒ 3 leptons+E/TI ZZ =⇒ 2 leptons+E/T or 4 leptons

N Vector boson productionI Z/γ∗ → ee, Z/γ∗ → µµ =⇒ 2 leptonsI Z/γ∗ → ττ =⇒ 2 leptons+E/TI W+jets/photon =⇒ 1 lepton+E/T

N Other componentsI Multijet production =⇒ No isolated leptonsI tt =⇒ 2 leptons+E/TI Υ → ee, Υ → µµ =⇒ 2 leptons

• All backgrounds except QCD from Monte Carlo

N QCD contribution determined from datainverting some of the lepton ID criteria

15 20 25 30 35 40 45 50 55 60

-210

-110

1

10

210

310

410

510

15 20 25 30 35 40 45 50 55 60

-210

-110

1

10

210

310

410

510

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

-1DØ RunII Preliminary 1.1 fb

M(e,e) [GeV]

Eve

nts

/ 2.

5 G

eV

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 + 2nu

QCDSUSY

[GeV]T EE

ven

ts /

1 G

eV -1DØ RunII Preliminary 1.1 fb


Selection Strategy

1. Dilepton+track analysis

N Require two reconstructed leptons (either e or µ)N Require significant E/T to account for escaping neutralinos/neutrinosN Require one additional isolated high quality track

I Higher efficiency than reconstructed third leptonI Efficient for e, µ and τ

• For some parameter points the third lepton has very low pT

• Dilepton+track analysis becomes inefficient

2. Likesign dilepton analysis

N Require two reconstructed leptons of the same chargeN Require significant E/T to account for escaping neutralinos/neutrinosN No requirement for a third object


ee + ` Selection

• Preselection

N Two good reconstructed electronsI pT > 12 GeV and pT > 8 GeV

• Anti–Z/γ∗ → ee cuts

N Small invariant massI 18 GeV < mee < 60 GeV

N Not back–to–backI ∆φee < 2.9

• Anti–tt cut

N Reject events with large jet activityI Sum of all jet momenta < 80 GeV

• Third isolated track

N Transverse momentum p`T > 4 GeV

I Isolated in tracker and calorimeter

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

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

Transverse momentum [GeV]E

ven

ts /

1 G

eV -1DØ RunII Preliminary 1.1 fb


ee + ` Selection (2)

• E/T related cuts

N E/T > 22 GeVN Transverse mass mT =

√

pT · E/T · (1 − ∆Φ(e, E/T )) > 20 GeVN Significance of E/T > 8

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 + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

) [GeV]2

, Mtr1

min(Mtr

Eve

nts

/ 1

GeV -1DØ RunII Preliminary 1.1 fb

0 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

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

)TESig(

Eve

nts


• E/T and track

N Product of E/T and track pT

I E/T × pT > 220 GeV2

0 100 200 300 400 500 600 700 800 900 1000

-310

-210

-110

1

10

210

310

0 100 200 300 400 500 600 700 800 900 1000

-310

-210

-110

1

10

210

310

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

[GeV ^2]l3

TMET X p

Eve

nts

/ 10

GeV

^2

-1DØ RunII Preliminary, 1.1 fb


ee + ` Selection (2)


N E/T > 22 GeVN Transverse mass mT =

√

pT · E/T · (1 − ∆Φ(e, E/T )) > 20 GeVN Significance of E/T > 8

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 + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

) [GeV]2

, Mtr1

min(Mtr

Eve

nts

/ 1

GeV -1DØ RunII Preliminary 1.1 fb

0 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

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

)TESig(

Eve

nts


• E/T and track

N Product of E/T and track pT

I E/T × pT > 220 GeV2

0 100 200 300 400 500 600 700 800 900 1000

-310

-210

-110

1

10

210

310

0 100 200 300 400 500 600 700 800 900 1000

-310

-210

-110

1

10

210

310

Data

ee→Z

tautau→Z

e nu →W

ee→Y

tt 2l 2b

WW 2l + 2nu

WZ 3l + nu

ZZ 4l or 2l + 2nu

QCD

SUSY

[GeV ^2]l3

TMET X p

Eve

nts

/ 10

GeV

^2

-1DØ RunII Preliminary, 1.1 fb


Likesign µµ Selection

• Preselection

N Two good muons of same chargeI pT > 5 GeV for both muons

N Not back–to–backI ∆φµµ < 2.9

• Anti–Z/γ∗ → µµ cuts

N Small invariant mass for OS pairsI 25 GeV < mµµ < 65 GeV

• Tightened pT cuts

N pT > 13 GeV and pT > 8 GeV

)2 (GeV/c±µ±µm0 20 40 60 80 100 120 140

2ev

ents

/ 1

GeV

/c

-210

-110

1

10

210

310

)2 (GeV/c±µ±µm0 20 40 60 80 100 120 140

2ev

ents

/ 1

GeV

/c

-210

-110

1

10

210

310

-1D0 Run II preliminary, 0.9 fbsignal

WZWWZZ

νµ→W

incl→tt+Xνµ→bW+b+Xµµ→bZ+b

-τ+τ→Z-µ+µ→Z

-µ+µ→1sΥQCDdata

)2 (GeV/c-µ+µm0 20 40 60 80 100 120 140

2ev

ents

/ 1

GeV

/c-210

-110

1

10

210

310

)2 (GeV/c-µ+µm0 20 40 60 80 100 120 140

2ev

ents

/ 1

GeV

/c-210

-110

1

10

210

310-1D0 Run II preliminary, 0.9 fb

signal

WZWWZZ

νµ→W





Likesign µµ Selection (2)


N 15 GeV < mT < 65 GeVN E/T > 10 GeVN Significance of E/T > 12N E/T × pT of trailing muon > 160 GeV2

)2,next to leading muon) (GeV/cTE(Tm0 20 40 60 80 100 120 140 160

2ev

ents

/ 1

GeV

/c

-210

-110

1

10

210

310

)2,next to leading muon) (GeV/cTE(Tm0 20 40 60 80 100 120 140 160

2ev

ents

/ 1

GeV

/c

-210

-110

1

10

210

310


WZWWZZ

νµ→W




)1/2) (GeVTESig(0 5 10 15 20 25 30

1/2

even

ts /

1 G

eV

-210

-110

1

10

210

310

)1/2) (GeVTESig(0 5 10 15 20 25 30

1/2

even

ts /

1 G

eV

-210

-110

1

10

210

310


WZWWZZ

νµ→W




/c)2 (GeVT

next to leading p× TE0 100 200 300 400 500 600 700 800 900 1000

/c2ev

ents

/ 10

GeV

-210

-110

1

10

210

310

410

/c)2 (GeVT

next to leading p× TE0 100 200 300 400 500 600 700 800 900 1000

/c2ev

ents

/ 10

GeV

-210

-110

1

10

210

310

410-1D0 Run II preliminary, 0.9 fb

signal

WZWWZZ

νµ→W





Final Event Numbers

• ee + ` selectionN Expected: 0.76 ± 0.67 events Observed: 0 eventsN Signal expectations: 1.69 ± 0.01 – 4.73 ± 0.02 eventsN Dominant background: Diboson production, Z/γ∗ → ττ

• Likesign µµ selection

N Expected: 1.1 ± 0.4 events Observed: 1 eventN Signal expectations: 0.61 ± 0.01 – 3.76 ± 0.15 eventsN Dominant background: Diboson production, Z/γ∗ → µµ

• eµ + ` selectionN Expected: 0.31 ± 0.15 events Observed: 0 eventsN Signal expectations: 0.70 ± 0.03 – 2.45 ± 0.09 eventsN Dominant background: Diboson production

• µµ + ` selectionN Expected: 1.75 ± 0.57 events Observed: 1 eventsN Signal expectations: 0.47 ± 0.02 – 1.94 ± 0.08 eventsN Dominant background: QCD, Z/γ production


Current Result

• Three reference scenariosN "3l–max": Maximize leptonic BR of chargino and neutralino ⇒ mχ0

2≈ m˜

N "Large–m0": Decays via W/Z bosons dominant ⇒ Small leptonic BRN "Heavy–squarks": Relax scalar mass unification

⇒ Increased production cross section

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

BR

(3l)

(p

b)

×) 20 χ∼1± χ∼ (σ

0

0.1

0.2

0.3

0.4

0.5

)20

χ∼)>M(l~); M(10

χ∼2M(≈)20

χ∼M(≈)1±

χ∼M(

>0, no slepton mixingµ=3, βtan

-1DØ Run II Preliminary, 0.3-1.1 fb

LEP

3l-max

heavy-squarks

0large-m

Observed LimitExpected Limit

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

BR

(3l)

(p

b)

×) 20 χ∼1± χ∼ (σ

0

0.1

0.2

0.3

0.4

0.5

• Mass limit for "3l–max" scenario

N mχ±

1

> 140 GeV

• Mass limit from PRL

N mχ±

1

> 116 GeV


Conclusion and Outlook

• Summary

N New search for charginos and neutralinos with 1 fb−1 of DØ dataN No evidence for signalN Chargino mass limit of 140 GeV in scenario with enhanced leptonic BR

• Outlook

N Still room for lot of improvementN Update µµ + ` and eµ + ` channelsN Include final states involving τ ’s

Chargino Mass (GeV)100 120 140 160 180 200 220 240

BR

(3l)

(p

b)

×) 20 χ∼1± χ∼ (σ

-210

-110

3l+X→ 02χ∼

±1χ∼Search for

)20

χ∼)>M(l~); M(10

χ∼2M(≈)20

χ∼M(≈)1±

χ∼M(


LE

P

3l-max

0

large-m

-11.0 fb

-12.0 fb

-14.0 fb

-18.0 fb


Conclusion and Outlook

• Summary

N New search for charginos and neutralinos with 1 fb−1 of DØ dataN No evidence for signalN Chargino mass limit of 140 GeV in scenario with enhanced leptonic BR

• Outlook

N Still room for lot of improvementN Update µµ + ` and eµ + ` channelsN Include final states involving τ ’s

Chargino Mass (GeV)100 120 140 160 180 200 220 240

BR

(3l)

(p

b)

×) 20 χ∼1± χ∼ (σ

-210

-110

3l+X→ 02χ∼

±1χ∼Search for

)20

χ∼)>M(l~); M(10

χ∼2M(≈)20

χ∼M(≈)1±

χ∼M(


LE

P

3l-max

0

large-m

-11.0 fb

-12.0 fb

-14.0 fb

-18.0 fb


Documents

Search for Charginos and Neutralinos with the DØ Detectorsusy06.physics.uci.edu/talks/1/hohlfeld.pdfSearch for Charginos and Neutralinos with the DØ Detector Marc Hohlfeld Laboratoire