search for charginos and neutralinos with the dØ...
TRANSCRIPT
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 2/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 3/17
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)
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 4/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 5/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 5/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 5/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 5/17
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~
~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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 6/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 7/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 8/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 9/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 10/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 11/17
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
-1DØ RunII Preliminary 1.1 fb
• 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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 12/17
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
-1DØ RunII Preliminary 1.1 fb
• 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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 12/17
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
incl→tt+Xνµ→bW+b+Xµµ→bZ+b
-τ+τ→Z-µ+µ→Z
-µ+µ→1sΥQCDdata
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 13/17
Likesign µµ Selection (2)
• E/T related cuts
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
-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
)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
-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
/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
incl→tt+Xνµ→bW+b+Xµµ→bZ+b
-τ+τ→Z-µ+µ→Z
-µ+µ→1sΥQCDdata
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 14/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 15/17
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
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 16/17
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(
>0, no slepton mixingµ=3, βtan
LE
P
3l-max
0
large-m
-11.0 fb
-12.0 fb
-14.0 fb
-18.0 fb
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 17/17
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(
>0, no slepton mixingµ=3, βtan
LE
P
3l-max
0
large-m
-11.0 fb
-12.0 fb
-14.0 fb
-18.0 fb
SUSY 2006, 06/13/2006 Marc Hohlfeld – p. 17/17