Transcript SUSY Searches at the Tevatron

SUSY Searches at the Tevatron
Rencontres de Moriond, QCD
March 2006
Else Lytken, Purdue University
for the CDF and D0 collaborations
Outline
 Brief intro to supersymmetry
 SUSY at the Tevatron
 Some selected analyses:
Squarks and gluinos,
incl scalar top and stopped
gluinos
Photon signatures
Lepton signatures,
incl Bs  and RPV
 Conclusion and outlook
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Supersymmetry in 60 seconds
Idea: extend SM with symmetry
fermions  bosons
If 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
5 higgses
h0,H0,A, H±
~
sleptons l
squarks q~
1/2
gluino g~
leptons
quarks
gauginos ~±
~0
1
gauge
bosons
3( B L)  2s
New quantum number
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often assumed conserved
R  ( 1)
3/2
gravitino
~
G
2
graviton
G
+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:
Lightest Susy
- Missing transverse energy (MET) from stable LSP’s Particle
- multijets from cascade decays
- multileptons
mb Q
C
D
b
Main challenge is the small expected
production cross section
 Need to model SM backgrounds very well
EWK
 Most searches check predictions in
nb
control regions before looking at data
top
containing possible signal
pb
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SUSY,
Exotics
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MET + jets: squark and gluino
Generic squarks and gluinos strongly produced
Cross section @ Tevatron: ~ a few pb
Expect cascade decays
Signature: 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] GeV
BothMoriond
experiments
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Search for Scalar top
Look for pair production of lightest stop quark
~0
Assume equal BR to e, ,, and ~
1
~
LEP limit: m  45 GeV
Event signature:
_
±
+ + MET
2
b-jets,
e
µ
cut on N
Limit for eµ
non-iso tracks
Signal regions optimized for M=m~t - m~
SM
expected
Obs
M: 20-40 GeV 16.43±1.07
22.99±3.10
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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
L=350 pb-1
Signal
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Limit combining with previous result in the µµ channel
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Stopped gluinos
Assume MSUSY(scalars) >> MSUSY(fermions)
 gluino can have long lifetime and hadronize (”R-hadrons”)
If lifetime > 10 µs:
• fraction of ~
g’s stopped in calorimeters
no good vertex
• stopped gluino  g + ~ 01
• later bunch crossing: single high ET shower and high MET
Background: cosmic muons
M= 50, 90, 200 GeV
3
1
2
Bkg
Obs
1
48
46
2
38
32
3
22
27
4
10
14
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Theory (hep-ph/0506242)
prediction
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MET + photons
In Gauge Mediated SUSY breaking
models, LSP is gravitino.
Typical signature from  decay:
NLSP
LSP
~
1  G
~ 0
Assume
prompt
decay
Signature: 2 energetic photons + MET
NLO
QCD background normalized to data
below MET of 12 GeV
Observed
Observe 4 events with MET45 GeV
Expecting 2.1±0.7 with 760pb-1
~±
New limit: m(
) 220 GeV
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Previous limit (CDF + D0):Else209
GeV
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MET + 3 leptons
Expected signature from chargino-neutralino production
Clean signature very attractive for the Tevatron
~
~
 10
q
0

W*
2
~
q


1
~
0
1
~
 1
~

W*
 20

Z*


D0, 6 channels: Expects: 3.85±0.75, Observes : 4. Signal would be 3-10 events
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3 leptons: continued
Channel
Example SM
signal
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
0.5±0.1
1
(600pb-1)
0.7±0.03
CDF:
All observations in
agreement with SM
predictions
Stay
tuned
forQCD
updated
limits!
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R
/ P SUSY: Long-lived LSP
Scenario: Weak RP violation (inspired by NuTeV dimuon excess)
Low mass LSP decays to 2+, r = [5;20]cm, other  escapes
l
(~5 GeV)
q
q-
Bkg estimated from data
Several cross checks
Diff as systematics
~
q
~ 0
1
~ 0
~ 0
1

~
l
1
l
Now excluding that these
events are SUSY  :
L=383pb-1
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Expect 0.8±1.5 events, Else
observe
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R/ P: 4 leptons
Now assume prompt decay
4 leptons from ~~
 decays
Analysis 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 background
No cut on MET or N jets
Expects 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 
Rare decay, SM branching frac ~10-9
Loop diagrams with sparticles (or direct
hep-ph/0507233 decay if RPV) enhance orders of magnitude
Previous limit:
Important at high tan
• 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
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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 .....
1fb-1
The hunt continues ...!
We have 1fb-1 ready for analysis and the
Tevatron is in great shape!
Expect 4-8 fb-1 by end of Run II
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Backup
Indirect constraint: BS 
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
CDF also looks at Bd 
Background estimation: linear extrapolation
from sidebands
Normalizing using B+- + K+
- Results compatible with SM backgrounds
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Look in the Bs and Bd Signal Window
LR > 0.99
CMU-CMX Channel:
CMU-CMU Channel:
Expect
Observed
Expect
Observed
Prob
0
Bs 0.88±0.30
1
67% Bs 0.39±0.21
Bd 2006
0.59±0.21
0
Bd 1.86±0.34
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Prob
68%
55%
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MET + jets: squark and gluino
Generic squarks and gluinos strongly produced
Cross section @ Tevatron: ~ a few pb
Expect cascade decays
Signature: lots of MET and  2 jets
D0 result:
• 2, 3, or 4 jets for the cases:
M~g > M~ q M~g ~ M~q and M~g < M~ q
• Dominant background differ
Z+jets, W+jets, tt, QCD
• MET > [75, 100, 175] GeV
• Lepton veto
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4 jets: Fit to QCD
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MET+jets continue
Expect 4.1 events, observe 3
CDF:
• Req.  3 jets and MET>165 GeV
• Bkg dominated by Z + jets
• Check: compare data and QCD
MC in jet domimated region
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D0 STRATEGY
Data pre-selection: 2 jets  2 jets  165º

 pT  40 GeV
jets
Luminosity: 310 pb-1
MET  40 GeV

H T   p T  50
jets
ANALYSIS STRATEGY
Distinguishes 3 approaches (dominant  )
M~g > Mq~
Search for acoplanar dijet
events (squark  jet + MET
dominant)
Mg~ < Mq~
Mg~ ~ Mq~
Search for events with at
Search for events with at least
least 4 jets (gluino  2 jets + 3 jets (2 jets from gluino and
MET dominant)
one from squark)
JET BACKGROUND STRATEGY
Cuts will remove its contribution.
Otherwise, contribution extrapolated from data behavior at low missing ET region.
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CDF Trilepton events
Next-to-leading
e-, pT = 12 GeV
MET
CMIO
CMUP
Leading electron
e+, pT = 41 GeV
CMX
MET, 45 GeV
Isolated track, pT = 4 GeV
Muon?
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Mass OS1
41.6
GeV
Mass OS2
27.0
GeV
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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
-1
σ ≤Else
0.239
with
Lytken, (
Moriond
2006 160 pb
122)QCD
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Conversion removal SF
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