Jianming Qian The University of Michigan for the CDF and ...qianj/susy99.pdf · yyyyyyyyyyyyyyyyyyyyyyyyy yyyyyyyyyyyyyyyyyyyyyyyyy yyyyyyyyyyyyyyyyyyyyyyyyy 0 100 200 300 400 500

Jianming QianJianming QianThe University of Michigan

(for the CDF and DØ Collaborations)

• Introduction• Searches for Charged Higgs Bosons• Searches with R-parity Conservation• Searches with R-parity Violation• GMSB Supersymmetry Searches

Supersymmetry’99 — Fermilab, June 14, 1999

An integrated luminosity of about 100 pb-1

was recorded per detector at TeVs = 18.

Tevatron Run I Collider

Run I Detectors

Tracking

D0 LIQUID ARGON CALORIMETER

1m

CENTRAL CALORIMETER

END CALORIMETER

Outer Hadronic(Coarse)

Middle Hadronic(Fine & Coarse)

Inner Hadronic(Fine & Coarse)

Electromagnetic

Coarse Hadronic

Fine Hadronic

Electromagnetic

DØ

l± b

Calorimetere ET/ γ /

Supersymmetry Menu

A lot has been done and published,~8 publications for CDF and ~11 for DØ

But none is what we have wanted...

The lightest supersymmetric particle (LSP) is assumed to be

either the lightest neutralino and a light gravitino

Searches with R-parity conservationjets

dilepton+jetstrilepton

photonic signatures

Searches with R-parity violationdilepton+jetsfour-lepton

Results are often interpreted in models• minimal supersymmetric extension of SM (MSSM)• minimal super-gravity models (mSUGRA)• models with gauge-mediated supersymmetry breaking (GMSB)

1 fb

1 pb

1 nb

1 µb

1 mb

Cross Section

Jet

bb_

W/Z

tt_

HiggsNew ?

1

103

106

109

1012

Events

pp_ → X

TeV 8.1s =

Challenges

The cross section for new physics is smallcompared with dominant Standard Model processes

(DØ e–identification: ~75% efficiency and 10 -4 fake rate)

Leptons (e, µ) and ET are the keys • missing ET resolution• lepton identification efficiency and fake rate

Search for Charged Higgs

If charged Higgs bosons are sufficiently light, they can be produced in top quark decays

t Hb→

Therefore, it will compete with the SM modet Wb→

Since H± and W± decay differently

W qq H cs Wbb→ →lν τ ν, ’ , ,

t→ Hb will lead to different signatures fortop quark pair events

Both CDF and DØ searched forcharged Higgs boson production in top quark pair events

Direct searches at LEP GeVMH > 69CLEO has set an indirect limit from to be

> + / ( ) .b s

MH

→ γβ244 63 1 3tan

Signature for H production in events• disappearance of standard WWbb signature• anomalous τ lepton production

tt


DØ searched for charged Higgs bosonsin decays of pair-produced top quarks from the disappearance of SM WWbb signature

hep-ex/9902028

For the top quark analyses, DØ observed 30 events with 11.2±2.0 expected background events

Assuming Br(t→Wb)=100%, the measured top-pair cross section agrees well with the SM prediction

0

2

4

6

8

10

12

14

16

18

20

140 150 160 170 180 190 200Top Quark Mass (GeV/c2)

Cro

ss S

ectio

n (p

b)

Laenen et al.

Berger et al.

Catani et al.

DØ


The analysis was restricted to the regions with valid leading-order calculationsσ( )tt = 5.5, 5.0, 4.5 pb

Sensitive only to the regionsof parameter space with largeBr(t→Hb)

Sensitive only to topologiesdifferent from WWbb of theSM top quark pair

H cs→ , τ ν

How much disappeareddepends on how muchexpected

DØ


CDF also searched for t→ Hb decay viatt disappearance

and τ appearance for high tanβ (where H→τν)Phys. Rev. D54, 735 (1996)

For the τ appearance analyses,τjjX and acoplanar ττ events were searched

The major backgrounds are fake taus,W+jets, Z+jets and WW, WZ, ZZ productions

7 events were observed with 7.4±2.0 events expected

No excess of events

60

80

100

120

140

160

180

200

10-1

1 10 102

60

80

100

120

140

160

180

200

10-1

1 10 102

Both CDF (106 pb–1) and DØ (~90 pb–1) searchedfor eee, eeµ, eµµ, µµµ events in Run I

Phys. Rev. Letters 80, 5275 (1998)Phys. Rev. Letters 80, 1591 (1998)

Search for Production~ ~χ χ1 20±

Backgrounds• WZ, ZZ• Zb, Wbb• top pair• Z/γ+fake lepton

No events were observed in either experimentThe expected # of background events is 1.2±0.2 for CDF

and 1.3±0.4 for DØ

q

q_´

W*χ~

1±

χ~0

1

W*

χ~0

2

χ~0

1

Z*

l

l

l

ν

Selection• 3 or more leptons with varying ET

• require e+e– or µ+µ– (CDF only)• ET>10 – 15 GeV• lepton – lepton correlation cut• resonance removal

Production of will lead to trilepton eventswith E one of the cleanest signature for supersymmetry

1

T

~ ~

,χ χ±

20

The null results were interpreted within the frameworkof MSSM models which give

1M M M~ ~ ~χ χ χ± ≈ ≈

20

102

The typical efficiency is 3-12% for CDF and 2-6% for DØ when

chargino mass is varied from 50 to 100 GeV

Trilepton for SUSY discovery?

Search for Production~ ~χ χ1 20±

10-2

10-1

1

10

50 60 70 80 90 100 110

M(χ∼±

1) (GeV/c2)

σ⋅B

r(χ∼

± 1χ∼0 2→

trile

pton

s +

X)

(pb)

CDF Preliminary ∫ L dt = 106 pb-1

CDF 95% C.L. Upper Limit

D∅ 95% C.L. Upper Limit

minimal SUGRA tan β = 2

A = 0 µ < 0

a)

b)

c)

d)

m0 = 2500 GeV/c2

m0 = 100 GeV/c2

Dilepton was said top quark discovery

Search for Light Stop

In many supersymmetry models, stop (and sbottom)can be significantly lighter than other squarks

q

q

g

1~t

1~t

01

~χ

01

~χ

c

c1~t

01

~χ+1

~χ

cb

*W

If and then

m m mm m m

Br t c

t t

t b

~ ~

~ ~

(~ ~ )

1 10

1 1

1 10 100%

< +< +

→ =±

χ

χ

χ

Backgrounds:• W+jets and Z+jets• top • diboson• QCD multijet

t∼1 → cχ

∼10

t∼1 → bχ

∼1+

t∼1 → bWχ

∼10 t

∼1 → tχ

∼10

Selection (CDF):• 2 or 3 jets with ET>15 GeV• ET>40 GeV• ET – jet correlation cut• jet – jet correlation cut• at least one charm-tagged jet

Signature: two acoplanar charm-jets with ET

(see the parallel session talk by Stephen Worm)

Search for Light Stop

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

BR (t∼1 → c + χ

∼10) = 100%

max t∼-Z0 coupling

min t∼-Z0 coupling

D0/7.4 pb-1

ALEPH√s=189 GeV

M(t∼ 1)

=M(c

)+M

(χ∼ 10 )

M(t∼ 1)

=M(b

)+M

(W)+

M(χ∼ 10 )

CDF 95% CLexcluded

M(t∼1) (GeV/c2)

M(χ∼ 10 ) (

GeV

/c2 )

CDF Preliminary88 pb-1

Data Sample: 88 pb–1

Events observed: 11Expected background: 15±4

No excess of events 10-1

1

10

10 2

10-6

10-5

10-4

10-3

10-2

10-1

1

Data - 88 pb-1

W/Z/Top + QCD

t∼1 110 GeV/c2 LSP 40 GeV/c2

b∼

1 140 GeV/c2 LSP 40 GeV/c2

min JP

Jet probability constructedusing the SVX informationto tag charm-jets:min JP < 0.05

CDF

Search for Sbottom

0

10

20

30

40

50

60

70

80

90

0 20 40 60 80 100 120 140

BR (b∼

1 → b + χ∼

10) = 100%

max b∼-Z0 coupling

min b∼-Z0 coupling

D0/RUN I

ALEPH√s=189 GeV

M(b

∼ 1)=

M(b

)+M

(χ∼ 10 )

CDF 95% CLexcluded

M(b∼

1) (GeV/c2)

M(χ∼ 10 )

(G

eV/c

2 )

CDF Preliminary88 pb-1

Assuming pair production of will yield two acoplanar - jets

Br b bb

b

(~ ~ )

~1 10

1

100%→ =χ

Replacing the charm-tag (min JP < 0.05) with the b-tag (min JP < 0.01), CDF observed 5 events

with 6±2 expected background events

DØ carried out a similar analysis exceptthat b-jets have to be tagged with less efficient soft-µ

No excess of events

b~

1

χ~

10

b

Squarks and gluinos can be copiously produced at Tevatron if they are light

Backgrounds:• QCD multijet• top quark pair• W/Z+jets

Search for and ~ ~q g

Shape analysis to estimate residual QCD background

The signature for productionis therefore jets + E eventsT

pp qq qg gg X→ +/

~~, ~~, ~~

Selection:• 3 or more jets with ET>25 GeV• Leading jet ET>115 GeV• ET>75 GeV• ET – jet correlation cut• optimized ET – HT cut

DØ (80 pb–1) searched for events with jets+EThep-ex/9902013

q~

χ~

i0

q

g~

q~

q

χ~

i0

q

0 50 100 150 200 250 3000

50

100

m0 (GeV/c2)

m1/

2 (G

eV/c

2 )msquark = 250 GeV/c2

mgluino = 300 GeV/c2


The analysis was optimized for mSUGRA modelswith A0=0, tanβ=2, µ<0using the next-to-leading order cross section by PROSPINO

No excess of events

Detection efficiency istypically a few percent for the signal

mm

q

g

~

~

>>

250260

GeV GeV

@ 95% C.L.

mq

=

mg~

~

CD

F D

ilept

on

Previous DØ Jets + ET(MSSM)

This experiment95% CL Jets + ET(MLES: tan = 2, A0 = 0, < 0)

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1/U

A2

DELPHI / Mark II

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0 100 200 300 400 500 6000

100

200

300

400

CDF Jets + ET

mgluino (GeV/c2)

msq

uark

(G

eV/c

2 )

mq < m

No correspondingMLES model

95% C.L. Excluded Region

DØ Preliminary

LEP I Excluded(dotted lines)

tan 2.0

3.0

4.0

5.06.0

β

Excluded

m0 in GeV/c2

m1/

2 in

GeV

/c2

µ < 0A0 = 0

0

20

40

60

80

100

0 50 100 150 200 250 300


Signature: dilepton accompanied by two jets

Criteria were optimizedfor every MC pointstudied to achievemaximum S-Bdiscrimination

No excess is observed

Selection:• two leptons with varying ET requirement• two jets with

• ET>20, 30, 40 GeVET

min > 20 GeV

Squarks and gluinos can also result in dilepton final states

q

q_

gq~

q

χ~0

2

χ~0

1

Z*

q~

q

χ~±

1

χ~0

1

W*

l

l

q ’

q

(see the parallel session talk by Sailesh Chopra)


bb–/cc

–

t t–

CDF searched for eventsl l± ± jj

Backgrounds:• Drell-Yan• top, bottom, charm• diboson

0 events observed with 0.6±0.3 events expected from the backgrounds

Selection:• Two like-sign leptons with ET>11,5 GeV• two or more with ET>15 GeV• dilepton mass cuts• ET>25 GeV


CDF Preliminary (106 pb-1)

1

10

140 150 160 170 180 190 200 210

M(squark)>> M(gluino)

M(gluino) (GeV/c2)

σBr(

2l) (

pb

)

1

10

180 190 200 210 220 230 240 250 260 270

M(squark) ≈ M(gluino)

M(gluino) (GeV/c2)

σBr(

2l) (

pb

)

Interpreted in terms of production~~, ~~, ~~qq qg gg jj→ ± ±l lassuming 5 degenerate squarks

Leptons are produced in the decays of cascaded from and g~ , ~ ~ ~χ χ1 2

0± q

The total efficiency for the signal varies from 0.6% to 2.0%

The gauge and Lorentz symmetries allow to add thefollowing terms to the superpotential

λ λ λijk i j k ijk i j k ijk i j kL L E L Q D U D D+ +’ "

resulting lepton and baryon number violationsas well as R-parity violation

The L - violating and couplings will give rise to multilepton events at the Tevatron

λ λijk ijk’

Both CDF and DØ have searched for R-parityviolating supersymmetry in leptonic final states

The B- violating couplings will lead to events with multijet without

make it impossible to study at the Tevatron

λ"ijk

TE/

Assumptions:• Among all possible terms, only those R-parity violating terms with the same event topology dominate• Rp-violating decays of and are considered• The couplings are strong so that Rp-violating decays occur within the detector

~c ~χ10

Search for Supersymmetry/Rp

Signature: two electrons accompanied by four jets

Selection:• 2 or more electrons with ET>10, 15 GeV• 4 or more jets with ET>15 GeV• mee<76 GeV or mee>106 GeV• HT>150 GeV

Backgrounds:• Drell-Yan• Z→ττ→ee• tt→ee• Instrumental

In a sample of 96 pb–1, 2 events were observed with1.8±0.3 events expected from the background

No excess of events

DØ

~χ10 ~e

e

λ’1 jk

q j

qk

pp SUSY ee jets→ → → +~ ~χ χ10

10

studied the case that all couplings aresmall except within the framework of mSUGRA

/Rp

jkλ’1



The null results were interpreted in the minimal super-gravity models with A0=0, tanβ=2, 6, and µ<0and varying m0 and m1/2

The typical Br is about 2% for the signal

ε ⋅

mm

q

g

~

~

>>

250230

GeV GeV

@ 95% C.L.

mg̃ = 280 GeV/c2

mg̃ = 330 GeV/c2

mg̃ = 227 GeV/c2

mg̃ =

mq̃ m

q̃ = 243 G

eV/c 2

mq̃ =

273 GeV

/c 2

m0 (GeV/c2)

m1

/2 (

Ge

V/c

2)

No

EW

SB

ν̃ LSP

This experiment 95% C.L.

mg̃ (GeV/c2)

mq̃

(GeV

/c2 )

Excluded Region at 95% C.L.

No SUGRA model

in this region

DØ Preliminary

(see the parallel sessiontalk by Sailesh Chopra)

R/ P SUSY λ121 χ10 χ1

0 → llll

0

20

40

60

80

100

120

140

160

180

200

0 100 200 300 400 500

LSP = ν̃

Unphysical

Mq̃ =200 G

eV

Mq̃ =300 G

eV

Mq̃ =400 G

eV

M g̃=200 GeV

Mg̃=300 GeV

Mg̃=400 GeV

Mg̃=500 GeV

M0 [GeV]

M1/

2 [G

eV]

95% C.L. excluded

CDF Preliminary∫ L dt = 87.5 pb-1

ISAJET 7.20tanβ=2µ < 0

CDF studied the case with a dominant in the mSUGRA framework

121λ

Signature: Events with four leptonsSelection:• 4 leptons with ET>12 (1), 5 (3) GeV• ∆Rll>0.4• no isolation

Backgrounds:• • Instrumental

Event observed: 1Expected BG events: 1.3±0.4

~χ10

~ν i

l j

lk

ν i

λ ijk

pp SUSY X→ → → +~ ~χ χ10

10 llll

bb cc/


CDF searched like-sign dielectron events with two jets(Fermilab Pub-98/374-E)

pp gg cc cc cc d dpp qq q q qq qq qq

→ → ⇒ =→ → ⇒

+ +

± ±

~~ ( ~)( ~) ( )( )~~ ( ~ )( ~ ) ( ’ )( ’ )

~l l

l l

(m GeV)c 200

10

10χ χ

No event observed in a sample of 107 pb–1

consistent with the estimated # of background events

(See the parallel session talk by Maxwell Chertok)

R/ p g∼g∼ → e±e± + ≥ 2j

200

300

400

500

600

700

800

200 210 220 230 240 250 260 270 280 290 300

Br(c∼

L → ed)≥0.5

Br(c∼

L → ed)=1.0

M(g∼) (GeV/c2)

M(q∼

) (G

eV

/c2 )

CDFPRELIMINARY

107 pb-1

Excluded at95% C.L.

M(c∼

L) = 200 GeV/c2

tan β = 2Choudhury and RaychaudhuriPhys. Rev. D56, 1778 (1997).

0.050.060.070.080.090.1

0.2

0.3

0.4

0.50.60.70.80.9

1

2

100 150 200 250 300 350M(q

∼) (GeV/c2)

σ⋅B

r(q∼q∼_ →

e± e± +

≥ 2

j) (

pb

)

CDFPRELIMINARY

107 pb-1

95% C.L.upper limit

R/ p q∼q∼_ → q χ

∼01 q

_ χ∼0

1 → e±e± + ≥ 2j

Br to LS ee = 1/8

M(χ∼0

1)=M(q∼)/2

M(χ∼0

1)=M(q∼)-M(q)

M(g ∼

)=0.2 T

eV/c 2

M(g ∼

)=0.5 T

eV/c 2

M(g ∼

)=1 T

eV/c 2

Theor. σ(q∼q∼_): NLO - CTEQ3M

Beenakker et al., Z. Phys. C69 (1995).

Selection• two like-sign electrons with ET>15 GeV• two or more jets with ET>15 GeV• no significant ET


44.8 GeV

e1ET = 36 GeV γ2

ET = 30GeV

e CandidateET = 63 GeV

γ1ET = 36 GeV

eeγγETCandidate Event

ET = 55 GeV

The probability for the event to be resulted from knownprocess is small.

Phys. Rev. Letters 81, 1791 (1998)

It generated considerable theoretical interest

Much publicity has accompanied the CDF event.

It is unusual because isolated leptons, photons,and especially large ET are rare in the Standard Model

CDF eeγγET Event

Search for γγET Events

CDF studied the ET distributions of diphoton eventsthese distributions agree well with the expectations

Phys. Rev. D59, 092002 (1999)

Photon in Supersymmetry

In Gauge Mediated Models with NLSP=χ~0

1χ~0

1→γ G~

pp_→χ

~+χ~-→W+W-χ

~01χ

~01

pp_→e

~e~→eeχ

~01χ

~01

were proposed as possible explanations of the eventEllis et al., PLB 394 (1997), Ambrosanio et al., PRD 54, 5395 (1996), ...

Pair production of any supersymmetric particleswill result in γγE/ T+X events

if both χ~0

1 decay inside the detector

Within the framework of MSSM with the LSP=χ~0

1,a class of models with dominant

e~→e+χ

~

20 and χ

~

20→χ

~

10+γ

decays was also proposed as an explanation of the event

pp_→e

~e~→eeχ

~02χ

~02→eeγγχ

~01χ

~01

Kane et al., Phys. Rev. D55, 1372 (1997)

γγE/ T events are expected frompp

_→e

~e~, ν

~ν~, χ

~

20χ

~

20+X processes

γE/ T+jets events are expected frompp

_→q

~/g~→χ

~02+X processes

E/ T (GeV)

Even

ts

γγ sample

Background

(µ,M2)=(-160,400)(×10)

(µ,M2)=(600,180)(×10)

2

4

6

8

10

12

14

0 20 40 60 80 100 120 140 160 180 200

DØ (106 pb–1) searched for diphoton events withlarge transverse energy imbalancePhys. Rev. Letters 80, 442 (1998)

Two events survived with 2.3±0.9 expectedfrom background processes


Principal Backgroundsmultijet, direct photon, Wγ, W+jets, Z→ee

( )1 2012

25

E GeV | |< 1.1 or 1.5 <| |< 2.0(2) E GeV | |< 1.1 or 1.5 <| |< 2.0(3) E GeV

T1

T2

T

γ

γη ηη η

>>

/ >

µ (GeV)

M2 (

GeV

)

tanβ=2

Excluded

DØ bounds

LEP bounds

Suggested

0

50

100

150

200

250

300

350

400

-750 -500 -250 0 250 500 750


The null results were interpreted in terms of chargino and neutralino pair production

pp X GG Xi j→ → + → +~ ~ ~ ~ ~ ~χ χ χ χ γ γ10

10

M M W1 225

3= tan ϑ

M~χ1

150± > GeV @ 95% C.L.

Insensitive to the tanβ value assumed

within the framework of MSSM with LSP=

The (µ,M2) parameter space were explored assuminggaugino mass unification at the GUT scale

~G

Search for γET+≥2-Jets Events

E/ T (GeV)

Even

ts /

2.5

GeV

Backgroundγ + ≥ 2 jets

m(q~) = 150 GeV

m(q~) = 300 GeV (×10)

1

10

10 2

10 3

0 20 40 60 80 100 120 140

DØ (99 pb–1) also searched for single-photon events withjets and large missing transverse energy

Phys. Rev. Letters 82, 29 (1999)

318 events selected with 320±20 events expected

Principal BackgroundsQCD direct photon and multijet, W+jets, etc...

( )1 202 2025

E GeV, | |< 1.1 or 1.5 <| |< 2.0(2) N , E GeV with | |< 2.0(3) E GeV

T

j Tj

T

γ η ηη

>≥ >

/ >

The analysis was interpreted in terms of squark/gluino production within the model with

dominant decay~ ~χ χ γ2

010→ +

m(q~) (GeV)

σ ×

B (p

b)

m(q~) = m(g

~)

95% C.L. limitTheory

DØ

1

10

10 2

150 200 250 300 350 400

m m mm mm m

q q g

q g

g q

~ ~ ~

~ ~

~ ~

)))

> =>>

310240240

GeV ( GeV (heavy GeV (heavy

@ 95% C.L.

For the optimized cuts ET>45 GeV and HT>220 GeV5 events were observed while 8±6 events were expected

To increase the sensitivity to supersymmetry, event selection was optimized in ET–HT plane

Search for γET+≥2-Jets Events

Search for a Light G~

qq GGg qg GGq GGg→ → →~ ~ ~ ~ ~ ~ gg

Signature: high ET monojet events

Backgrounds:• W/Z+jets• top, diboson

Five eventsobserved while10±3 events areexpected

Fm

G

>> ×

2211 2 10

GeV eV-5

~ .

Selection:• ET>80 GeV for leading jet• ET>200 GeV• lepton veto and cleanup

If the gravitino is light and all other super-partnersare heavy, could be the only super-partner

produced at Tevatron~G

(See the parallel session talk by Andrea Castro)

Summary

No evidence against Supersymmetry

There are still a number of analyses going onthe effort is now being shifted toward Run II

Both CDF and DØ have searched for supersymmetry in leptonic and ET final states

Sresults = Exclusions (Run I)Results = Discoveries (Run II?)

− /− /− /− /− /− / →− / →

±

jets + E analyses: + jets + E analysis: + jets analysis:

+ E analyses: analysis:

+ jets + E analysis: + E analyses:

T

T

T0

T 20

T 10

~ ~ ~ ~ ~~ ~

~ ~

~ ~~ ~

t b q g Gq g

R

R

G

p

p

1

10

llll

lllllll

χ χ

γ χ χ γγ γ χ γ

Jianming Qian The University of Michigan for the CDF and ...qianj/susy99.pdf · yyyyyyyyyyyyyyyyyyyyyyyyy yyyyyyyyyyyyyyyyyyyyyyyyy yyyyyyyyyyyyyyyyyyyyyyyyy 0 100 200 300 400 500

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