SUSY Searches at the Tevatron
Rencontres de Moriond, QCD
March 2006
Else Lytken, Purdue Universityfor the CDF and D0 collaborations
Else Lytken, Moriond QCD 2006 2
Outline
Brief intro to supersymmetry SUSY at the Tevatron Some selected analyses:
Squarks and gluinos, incl scalar top and stopped
gluinosPhoton signaturesLepton signatures,
incl Bs and RPV
Conclusion and outlook
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Supersymmetry in 60 seconds
Idea: extend SM with symmetry fermions bosonsIf realized, lots of new particles to be found!
Many attractions: Low scale supersymmetry protects higgs mass, provides dark matter candidate, unification @1016 GeV, and consistent with precision top mass fits
Spin 0 1/2 1 3/25 higgses gluino g gauge gravitino h0,H0,A, H± leptons bosons Gsleptons l quarks 2squarks q gauginos ± graviton
0 G
New quantum numberoften assumed conserved
~
~
~
~
~
~
R PB L s ( ) ( )1 3 2 +1 SM
- 1 SUSY
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SUSY searches at the Tevatron
SUSY searches attractive from experimental point of view due to variety of signatures: - Missing transverse energy (MET) from stable LSP’s - multijets from cascade decays - multileptons
Main challenge is the small expected production cross section Need to model SM backgrounds very well Most searches check predictions in control regions before looking at data containing possible signal pb
nb
mb
b
top
SUSY,Exotics
QCD
EWK
Lightest SusyParticle
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MET + jets: squark and gluino
Generic squarks and gluinos strongly producedCross section @ Tevatron: ~ a few pb
Expect cascade decaysSignature: lots of MET and 2 jets
Results from D0: (310 pb-1) 2, 3, or 4 jets CDF: (250 pb-1) 3 jets Dominant backgrounds Z+jets, W+jets, tt, QCD• QCD fitted or cross checked with data• MET cut > [75;175] GeVBoth experiments see no hints of SUSY
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Signal regions optimized for M=mt - m
Search for Scalar top Look for pair production of lightest stop quarkAssume equal BR to e, ,, and LEP limit: m 45 GeVEvent signature: 2 b-jets, e±µ + MET Limit for eµ
L=350 pb-1 SignalSM expected
Obs
M: 20-40 GeV 16.43±1.07 22.99±3.10 21
M: 50-60 GeV 18.28±0.72 34.63±3.96 34
M: > 70 GeV 16.70±0.51 40.66±4.38 42
cut on N non-iso tracks
~ ~
~ ~
01
+_
~
Limit combining with previous result in the µµ channel
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Stopped gluinosAssume MSUSY(scalars) >> MSUSY(fermions) gluino can have long lifetime and hadronize (”R-hadrons”)If lifetime > 10 µs: • fraction of g’s stopped in calorimeters• stopped gluino g + • later bunch crossing: single high ET shower and high MET
Bkg Obs
1 48 46
2 38 32
3 22 27
4 10 14
01
~~
14
32
M= 50, 90, 200 GeV
Theory prediction
(hep-ph/0506242)
Background: cosmic muons
no good vertex
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MET + photons
New limit: m( ) 220 GeV Previous limit (CDF + D0): 209 GeV
In Gauge Mediated SUSY breaking models, LSP is gravitino.Typical signature from decay:
Signature: 2 energetic photons + MET
QCD background normalized to data below MET of 12 GeVObserve 4 events with MET45 GeVExpecting 2.1±0.7 with 760pb-1
Assumeprompt decay
Observed
NLO
±1
~
10 ~G~
NLSP LSP
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MET + 3 leptons
D0, 6 channels: Expects: 3.85±0.75, Observes : 4. Signal would be 3-10 events
Expected signature from chargino-neutralino productionClean signature very attractive for the Tevatron
~02
~
1
W*
q
q ~01~
1
W*
~01
~02
Z*
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3 leptons: continued
CDF: All observations in agreement with SM predictions
ChannelExample signal
SM expected
Obs
µµ/e +l (0.7fb-1) 2.3±0.3 1.2±0.2 1
ee+l (350pb-1) 0.5±0.06 0.2±0.05 0
µµ+l (low pt) (320pb-1) 0.2±0.03 0.1±0.03 0
ee+trk (600pb-1) 0.7±0.03 0.5±0.1 1
Stay tuned for updated limits!
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RP SUSY: Long-lived LSPScenario: Weak RP violation (inspired by NuTeV dimuon excess)Low mass LSP decays to 2+, r = [5;20]cm, other escapes
Now excluding that these
events are SUSY :
Bkg estimated from dataSeveral cross checksDiff as systematics
Expect 0.8±1.5 events, observe 0
~01
~01
~01
q
l
l
l~~
-
L=383pb-1
(~5 GeV)
/
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RP: 4 leptonsNow assume prompt decay 4 leptons from decaysAnalysis also looked at 3 leptons
~~
Yukawa term:
ijkLiLjEk
Analysis accepts e and µ sensitive to 121 and 122
_
Trilepton control regions
Striking signature, virtually no SM backgroundNo cut on MET or N jetsExpects 1.5±0.2 signal, <0.01 SM, observes 0
Limits on 121: < 0.21 pb 122 : < 0.11 pb
/
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Indirect constraint: BS
• Look for excess of µµ events in Bs and Bd mass windows • Background estimation: linear extrapolation from sidebands• Results compatible with SM backgrounds Br(Bs)<1.0×10-7 @ 95%CL --- Closing in on SUSY! ---
Rare decay, SM branching frac ~10-9
Loop diagrams with sparticles (or direct decay if RPV) enhance orders of magnitude
Important at high tan
Previous limit:
hep-ph/0507233
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Summary and outlook CDF and D0 keep probing new areas of the SUSY parameter space! Results can also constrain other models It is only limits so far .....
We have 1fb-1 ready for analysis and the Tevatron is in great shape! Expect 4-8 fb-1 by end of Run II
The hunt continues ...!1fb-1
Backup
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Indirect constraint: BS
CDF also looks at Bd Background estimation: linear extrapolationfrom sidebandsNormalizing using B+- + K+
- Results compatible with SM backgrounds
Rare decay, in SM branching frac ~10-9
Loop diagrams with sparticles (or direct decay if RPV) enhance orders of magnitude
Important at high tan
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Look in the Bs and Bd Signal Window
LR > 0.99
CMU-CMU Channel: Expect Observed ProbBs 0.88±0.30 1 67%Bd 1.86±0.34 2 63%
CMU-CMX Channel: Expect Observed ProbBs 0.39±0.21 0 68%Bd 0.59±0.21 0 55%
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MET + jets: squark and gluino
Generic squarks and gluinos strongly producedCross section @ Tevatron: ~ a few pb
Expect cascade decaysSignature: lots of MET and 2 jets
4 jets: Fit to QCD
D0 result:• 2, 3, or 4 jets for the cases:
and • Dominant background differ Z+jets, W+jets, tt, QCD• MET > [75, 100, 175] GeV• Lepton veto
Mg > Mq~ ~ Mg ~ Mq~ ~ Mg < Mq~ ~
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MET+jets continueCDF:
• Req. 3 jets and MET>165 GeV
• Bkg dominated by Z + jets
• Check: compare data and QCD MC in jet domimated region
Expect 4.1 events, observe 3
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D0 STRATEGY
Data pre-selection:
Luminosity: 310 pb-1
jets 2GeV 40MET
50pT jets
THº1652 jets GeV 40pT
jets
Distinguishes 3 approaches (dominant )
Search for acoplanar dijet events (squark jet + MET dominant)
Search for events with at least 4 jets (gluino 2 jets + MET dominant)
Search for events with at least 3 jets (2 jets from gluino and one from squark)
Mg < Mq~ ~Mg > Mq~ ~ Mg ~ Mq~ ~
Cuts will remove its contribution.
Otherwise, contribution extrapolated from data behavior at low missing ET region.
ANALYSIS ANALYSIS STRATEGYSTRATEGY
JET BACKGROUND JET BACKGROUND STRATEGYSTRATEGY
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CDF Trilepton events
Leading electrone+, pT = 41 GeV
Next-to-leadinge-, pT = 12 GeV
MET, 45 GeVIsolated track, pT = 4 GeV Muon?
Mass OS141.6 GeV
Mass OS227.0 GeV
CMIOMET
CMUP
CMX
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Limits
Combine 3 lepton and 4+ lepton signal regions to set limits.
Observed Limits (95% C.L.)
121 122
σ ≤ 0.21 pb σ ≤ 0.11 pb
Signal Point: M0 = 250, M1/2 = 260, tan = 5, > 0, = 0.143
Excluded by DØ: σ ≤ 0.116 (121) with 238 pb-1 σ ≤ 0.239 (122) with 160 pb-1
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Conversion removal SF
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