Jianming Qian The University of Michigan for the CDF and ...qianj/susy99.pdf ·...
Transcript of Jianming Qian The University of Michigan for the CDF and ...qianj/susy99.pdf ·...
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
Search for Charged Higgs
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
Search for Charged Higgs
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
Search for Charged Higgs
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
Search for and ~ ~q g
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
Search for and ~ ~q g
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)
Search for and ~ ~q g
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
Search for and ~ ~q g
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
Search for Supersymmetry/Rp
Search for Supersymmetry/Rp
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/
Search for Supersymmetry/Rp
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
Search for Supersymmetry/Rp
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
Search for γγET Events
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
Search for γγET Events
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