Supersymmetry at the LHC:
Searches, Discovery Windows, and
Expected Signatures
Darin Acosta
representing
ATLAS
&
Outline
Introduction to SUSY, LHC, and the Detectors
Non-Higgs sparticle searches:
Î Trigger Strategies
Î mSUGRA
ÎInclusive squark/gluino searches
ÎExclusive sparticle mass reconstruction
– neutralino
– sbottom, gluino
Î GMSB
Îstau (heavy lepton) search
ÎRadiative neutralino decay and lifetime
ÎCascade reconstruction
Summary
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Minimal SuperSymmetry
SUSY
Î Symmetry between bosons and fermions
~, ~l
q
Î Squarks/sleptons:
scalar counterparts to the fermions
~± , χ
~0
~
χ
ÎCharginos/neutralinos/gluinos: 1,2 1,2,3, 4 , g
fermion counterparts to SM gauge bosons
ÎAt least two Higgs doublets (5 scalars): h, H 0 , A, H ±
Î Avoids fine-tuning of SM, can lead to GUTs
MSSM
Î Usually consider RP ≡ (-1)3(B-L)+2S conserved
⇒ LSP is stable
Î 105 new parameters
mSUGRA:
Î Require SUSY to be a local symmetry
Î Universal gravitational interactions break SUSY
at scale F ~ (1011 GeV)2
Î 5 free parameters
Îm0 : Common scalar mass
Îm1/2 : Common gaugino mass
ÎA0 : Common scalar trilinear coupling
Îtan β : Ratio of v.e.v. of Higgs doublets
ÎSign(µ) : sign of Higgsino mixing parameter
d i d i d i
~f
M a g~f > M aq~f > M a χ
~± ≈ M χ
~ 0 ≈ 2M χ
~0
Î Typically: M χ
1
2
1
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Large Hadron Collider (LHC)
CMS
ATLAS
R = 4.5 km
E = 7 TeV
Two proton rings housed in same tunnel as LEP
Design luminosity: L = 1034 cm–2s–1 = 100 fb-1/year
(Pile up: ~20 collisions/crossing)
Start-up luminosity: L ~ 1033 cm–2s–1 = 10 fb-1/year
Completion: mid 2007
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mSUGRA Cross Sections @ LHC
q~, g~
m1/2 (GeV)
Total cross section
1400
1 fb
1200
1000
10 fb
TH
800
100 fb
600
1 pb
400
10 pb
200
EX
A0 = 0 , tan β = 35 , µ > 0
0
0
500
1000
1500
2000
m0 (GeV)
Î Squark/gluino production dominates total SUSY
cross-section for low to moderate m1/2
Î Cross sections don’t vary much with µ, tanβ
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Detectors
Tile CAL
toroids
4T solenoid
ATLAS
LAr CAL
2T solenoid
TRT and
Si tracker
muon
Cu/Scin HCAL
PbWO4 ECAL
Full Si tracker
Compact Muon Solenoid (CMS)
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SUSY Signatures
Complex squark/gluino decay chains
Î Many high-ET jets
Î Heavy-flavor (τ and b, especially at large tanβ)
Î Leptons
Î From sleptons, charginos, W/Z, and b-jets
Î Missing transverse energy (MET)
Î From LSP and neutrinos from taus, sneutrinos
Example:
m0 = 1000 GeV
m1/2 = 500 GeV
tan β = 35
µ>0
A0 = 0
CMS event
simulation
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Trigger Challenge
Reduce 40 MHz bx rate (1 GHz pp) → O(100 Hz)
Î Inclusive Jet Rate (cone algorithm, R=0.5):
Full GEANT-based
detector simulation on
QCD background
(used in preparation of
CMS DAQ Technical
Design Report)
L=2×1033
Î Expected MET Rate:
Recon. MET (hi lumi)
Recon. MET (low lumi)
Gen. MET (hi lumi)
Gen MET (low lumi)
Requiring a rate to
tape of a ~few Hz
implies an inclusive
single jet threshold
of 400–600GeV, and
an inclusive MET
threshold of
100–200 GeV
Reconstructed MET
rate below 100 GeV
mainly from
calorimeter energy
resolution
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SUSY Trigger Exercise (CMS)
Î Consider several points in the m0-m1/2 plane near
the Tevatron reach (most difficult for LHC)
Î Consider points with and without Rp conservation
~0 → 3j
χ
Î For Rp choose most difficult case: 1
Î Run full GEANT-based detector simulation on SUSY
signals and SM backgrounds to evaluate trigger
performance
Î Optimize efficiency for a rate to tape of 3 Hz
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Example Trigger Strategy (CMS)
Possible jet and MET triggers (at Level-2):
(for L=2×1033)
• MET >170 GeV
• 3 jets > 60 GeV and MET > 110 GeV
• 4 jets > 120 GeV
• 1 jet > 190 GeV, MET>90 GeV, and ∆φ(j1,j2) < π–0.5
• 2 jets>40 GeV, MET>100 GeV, and ∆φ(j1,j2) < π–0.5
• 4 jets>80 GeV, MET>60 GeV, and ∆φ(j1,j2) < π–0.5
Efficiency for SUSY points:
Î ε=0.78, 0.74, 0.54, 0.38, 0.27, 0.17
4
5
6
4R
2nd jet
5R
6R
With RP
1st jet
Background rate of ~3Hz
dominated by QCD
For completeness, inclusive lepton triggers are:
Î PT(electron)>25–30 GeV , PT(muon)>20 GeV
(for L=2×1033)
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Fast Simulation
Full simulation of signals and backgrounds like
that shown for trigger exercise is too CPU
intensive for complete SUSY reach
determination
Î Require O(108) events, but full GEANT
simulation takes tens of minutes per event
Î Use physics generators + parameterized
detector performance
ATLFAST:
Î Tracks (µ): ∆PT/PT = 0.4PT ⊕ 1% (PT in TeV)
Î EM resolution: σ/E ~ 10%/√E ⊕ 0.3% (E in GeV)
Î Jet resolution: σ/E ~ 60%/√E ⊕ 2% (E in GeV)
CMSJET:
Î Tracks (µ): ∆PT/PT = 0.15PT ⊕ 0.5% (PT in TeV)
Î EM resolution: σ/E ~ 5%/√E ⊕ 0.5% (E in GeV)
Î Jet resolution: σ/E ~ 100%/√E ⊕ 5% (E in GeV)
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~ g
~ Search
Inclusive q,
Counting excess events over SM background
Î Discovery mode SUSY search at LHC
Î Explicit mass reconstruction not done
6 Analyses:
Î ETmiss:
Î Ol:
Î 1l:
Î 2lOS:
Î 2lSS:
Î 3l:
jets+MET, no lepton requirements
no leptons
1 lepton
2 leptons, opposite sign
2 leptons, same sign
3 leptons
CMS Study:
Lepton identification
Î Electron: PT>20 GeV, isolated, |η|<2.4
Î Muon: PT>10 GeV, isolated or not, |η|<2.4
Vary cuts in 6 categories (~104 combinations)
Î #Jets, MET, Jet ET, ∆φ(l,MET), Circ., µ Iso.
Î Common cuts:
ÎMET>200 GeV, ≥2 jets, ETjet > 40 GeV, |η|<3
Optimize S/√(S+B) in a counting experiment
Î Probe 500 (m0, m1/2) points
Î ~106 signal events, ~108 QCD, tt, W/Z+jets
Plot 5σ sensitivity contours
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-1
1400
L dt = 100 fb
A0 = 0 , tan β= 35 , µ > 0
~
g(3000)
miss
ET
0l + 1l + 2l OS
-1
(300 fb )
)
h(123
miss
ET
1200
ISAJET 7.32 + CMSJET 4.5
m1/2 (GeV)
~ g
~ Reach
CMS q,
~
g(2500)
0l
1l
1000
~
~
25
q(
q(2
0
)
00
00)
TH
~
g(2000)
2l OS
800
2l SS
3l
~
g(1500)
600
~
q(
)
00
15
2
h =1
2
4
h = 0.
~
400
g(1000)
0)
00
q(1
~
5
0.1
2
h =
~
~
q(5
0
200
0)
g(500)
h(110)
EX
0
0
500
1000
1500
2000
m0 ( GeV)
Î Jets+MET search gives greatest sensitivity
Nucl. Phys. B547 (1999) 60
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m1/2 (GeV)
Jets+MET Reach vs. Luminosity
1400
L dt = 1, 10, 100, 300 fb-1
A0 = 0 , tan β= 35 , µ > 0
~
g(3000)
miss
ET
miss
ET
1200
CMS
-1
(300 fb )
)
h(123
-1
(100 fb )
~
g(2500)
1000
~
~
2
q(
q(2
50
000
0)
)
TH
~
g(2000)
miss
ET
800
-1
(10 fb )
~
g(1500)
600
~
miss
0)
50
1
q(
2
h =1
2
4
h = 0.
ET
-1
(1 fb )
~
400
g(1000)
q(1
~
0)
00
5
0.1
2
h =
~
~
q(5
200
00)
g(500)
h(110)
EX
0
0
500
1000
1500
2000
m0 ( GeV)
Î Squarks/gluinos probed to ~1.5 TeV with 1 fb-1
Î Up to 2.5 TeV at design luminosity (100 fb-1)
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Other Parameter Choices
ATLAS
TDR 15
CERN/LHCC 99-15
L=10 fb–1
1l
tan β = 10, µ < 0
0l
800
SS
600
3l
OS
2l,0j
400
3l,0j
200
0
1l
0l
800
tan β = 10, µ > 0
3l
SS
600
OS
400
2l,0j 3l,0j
200
0
0
500
1000
1500
2000
m0 (GeV)
Î Similar cuts and optimization as for CMS study
Î Sensitivity for lower tanβ also derived, but
lower mass Higgs inconsistent with present limits
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Exclusive Di-Lepton Reconstruction
Measure invariant mass distribution of
same flavor leptons as evidence for
~0 → χ
~ 0 l + l − or χ
~ 0 → ~l + l − →
χ
2
1
2
OS
~ 0l+l−
χ
1
~ 0 can be produced via Drell-Yan χ
~±χ
~0,
χ
2
1 2
~, g~
but more prevalent in cascade decays of q
Endpoint in mass spectrum exhibits sharp edge:
~0 → χ
~ 0l+ l−
χ
2
1
SUSY e+e− + µ+µ−
SM background
Events/4 GeV/30 fb −1
ATLAS “Point 4”:
m0=800GeV m1/2=200GeV
tanβ=10 µ>0 A0=0
L=30 fb–1
M( l+l−) (GeV)
This point selected by:
Some Z0 from other gauginos
SM background is small
Î Two OS leptons, PT>(20,10) GeV, |η|<2.5
Î MET>200 GeV, 4 jets: PT1>100 GeV, PT234>50 GeV
d i d i
c hie c h d ii c h
max
~0 − m χ
~0
=m χ
3-body decay endpoint: mll
2
1
2-body: m max = m 2 χ
~ 0 − m 2 ~l m 2 ~l − m 2 χ
~ 0 / m ~l
ll
2
1
e d i
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~ ~
Exclusive b, g Reconstruction
Completely reconstruct a SUSY decay chain:
p
l
b
~
χ 20
~
g
m
~±
l
~
b
~
χ10
l±
b
p
ATLAS Study
Î “Point 3” of TDR
Îm0=200 GeV, m1/2=100 GeV, tanβ=2, µ<0, A0=0
CMS Study
Î Investigate “Point B” of “Proposed Post-LEP
Benchmarks for SUSY” Eur.Phys.J.C22 (2001) 535
Î m0=100 GeV, m1/2=250 GeV, tanβ=10, µ>0, A0=0
af
c h
~ = 174 GeV
md χ
i
m g~ = 595 GeV, m bL, R = 496,524 GeV
0
2
~0
Start with reconstructing χ 2 :
Î Two OS isolated leptons,
PT>15 GeV, |η|<2.4
Î MET>50 GeV
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L=10 fb–1
CMS
SUSY
bkgnd
M(e + e - ) + M(µ + µ − )
D. Acosta, University of Florida
~
b Reconstruction
sbottom reconstruction:
Î Select window around di-lepton endpoint (16 GeV)
~ 0 rest frame with χ
~ 0 at rest
Î χ
2
1
F
d i GH
d i IJ pvdl l i
d iK
~ from di - lepton endpoint and
Can estimate md χ
i
~ ≈ 2m χ
md χ
i d~ i
~0
m χ
1
v ~0
p χ2 = 1+
m l+l−
+ −
0
1
0
2
0
1
but analysis not too sensitive to details
Î Add most energetic b-jet to reconstruct ~
b
Î Eb-jet>250 GeV, |η|<2.4
Î b-jet: ≥2 tracks with IP significance > 3σ
Î Require MET>150 GeV
Î Require E(ll)>100 GeV
Reconstructed mass in
reasonable agreement with
input (480 vs. 510 GeV)
L=10 fb–1
CMS
Resolution <10% with
assumption on LSP mass
(can’t resolve L/R mass
splitting, however)
Mass (GeV)
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~
g Reconstruction
Add another b-jet closest in φ to reconstruct ~g
CMS Point B
Reconstructed mass
in reasonable
agreement with input
(585 vs. 595 GeV)
L=10 fb–1
af ch
d i
~
~0 :
m g~ − m b is independent of m χ
1
ATLAS Point 3
Events/4 GeV/10 fb-1
20000
Mass (GeV)
CMS Point B
Expect 20 GeV
Expect 85 GeV
15000
10000
5000
0
0
20
40
60
M(χ2bb)-M(χ2b) GeV
80
100
Mass (GeV)
~ mass
Cut around g
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Minimal GMSB
Gauge Mediated Symmetry Breaking
Î Uses SM gauge interactions instead of gravity
to break SUSY
Î Solves FCNC problem
Î SUSY breaking scale much less than mSUGRA
scale √F << 1011 GeV
Î Particles get mass from SM gauge interactions
at a messenger scale Mm ~ O(1000 TeV) << MPl
Î n = number of SU(5) messenger fields
Λ = F / Mm ~ 100 TeV
~
G is LSP ( m << 1 GeV)
~
~0 → G
γ ( n = 1, low tan β )
NLSP: χ
1
~
~
l → Gl
(n > 1, high tan β )
Î NLSP lifetime:
F 100 GeVIJ FG F IJ
cτ ~ 1.3 mG
H M K H 1000 TeVK
5
4
NLSP
Î cτ >> detector size
Î slepton ( ~
τ ) is a long-lived heavy lepton (like µ)
Î neutralino leads to MET, like MSSM
Î cτ ~ detector size
Î Measure NLSP lifetime
Î Estimate F
Î cτ << detector size
Î radiative decay with γ
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~
GMSB Heavy Lepton (τ)
Search
1/β
Use drift-tube muon systems of ATLAS and CMS
to measure time-of-flight for heavy leptons
2
(σ ~ 1ns)
1.8
1.6
1.4
1.2
1
0.8
0.6
0
200
400
600
800 1000 1200 1400
momentum (GeV)
Î Measure 1/β and p ⇒ reconstruct mass
CMS:
particles / 20 GeV
Î Require 2 “muons” with PT>45 GeV, M>97 GeV
Î |η|<1 for CMS drift-tube system
Î Can measure stau mass from 90–700 GeV:
70
GMSB scenario:
n=3, tanβ=45,
Λ=50-300 TeV,
M/Λ=200
114GeV; L=1/fb; eff=5%
60
50
303GeV; L=10/fb; eff=15%
40
30
636GeV; L=100/fb; eff=26%
20
10
0
0
100 200 300 400 500 600 700 800 900 1000
reconstructed mass (GeV)
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~
GMSB N1 Lifetime Measurement
~
Look for N1 decays inside detectors:
1) Electromagnetic showers not pointing to vertex
ATLAS vertex resolution
for H→γγ
Events/0.2cm
Î Use fine angular resolution from
LAr EM calorimeter (ATLAS)
and PbWO4 crystals (CMS)
300
σ =1.33 cm
200
100
Î ATLAS: if no non-pointing γ’s
in 30 fb-1 ⇒ cτ > 100km
0
-10
-5
0
5
10
z cal o-ztrue (cm)
(Λ=90 TeV, M = 500 TeV, n=1)
2) Showers in muon system
Î Identify showers with high
hit multiplicity
σ+(cτ)/cτ
CMS: Overall sensitivity to measure cτ:
L=143/fb; effkin=10%
10
m(N1)=291GeV
ECAL counting
1
µ
CAL counting
ECAL/µ CAL
ECAL impact
µ
-1
CAL slope
COMBINED
10
10
-2
10
-1
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10
23
10
2
10
3
cτ (m)
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GMSB Cascade Search (CMS)
Consider the cascades
~
~
N2 → lR + l
~
→ N1 + l + + l −
~
~
N1 → lR + l
~
→ G + l+ + l−
or
(NLSP is neutralino)
(NLSP is slepton)
100
Λ = 30–90 TeV
M =120–300 TeV
n=3,4,5
SM
GMSB 1
GMSB 2
GMSB 3
GMSB 4
GMSB 5
75
50
Λ=30-200 TeV, M=40-30000 TeV, tanβ=1.5-55, signµ= ±1
25
0
Ñ1 Mass (GeV)
Number of lepton pairs/10 fb-1
which will lead to a detectable sharp endpoint in
the di-lepton invariant mass as in mSUGRA
1500
-25
-50
0
d
200
400
600
(ll) + − (GeV/c)
M e + e − + µ + µ − M− µ
e − e+ µ −
ee+mm-em
inv
i
edge>0, M/ < 1.8
edge>0, M/ > 1.8
eff=1
1000
eff=0.15
Î MET>200 GeV
Î 2 OS same flavor
leptons, PT>40 GeV
500
Î PT (jet4)>80 GeV
ss
s=
Ñ1
˜1
Ma
s
Ma
GMSB 1
GMSB 2
GMSB 3
Probe in 10 fb–1 :
m τ~1 < 350 GeV and
a f
~
mc N h < 500 GeV
GMSB 4
GMSB 5
0
0
200
1
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400
600
800
τ˜1 Mass (GeV)
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LHC Summary
Discovery of SUSY, if it exists, is almost assured
at the LHC
Î Inclusive mSUGRA squark/gluino discovery reach
to 1.5 TeV with 1 fb–1, 2.5 TeV with 100 fb–1
Î Difficult part will be untangling decay chains and
measuring masses
Possibility to reconstruct squark/gluino/neutralino
decays in mSUGRA and GMSB in several
prototype analyses
Trigger strategies identified for efficient coverage
Ability exists to identify heavy leptons in GMSB
scenarios, as well as NLSP lifetime in radiative
decays
Many more exhaustive SUSY studies at the LHC
experiments are available:
Î ATLAS TDR 15 CERN/LHCC 99-15
Î CMS Note 1998/006
Looking forward to studying SUSY spectroscopy
before the end of the decade !
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Can mSUGRA Escape LHC?
M.Battaglia et al., Eur.Phys.J. C22 (2001) 535
proposed several SUSY benchmark points in
the post-LEP era
Two of them would lead to sparticles beyond the
reach of the LHC except for a light Higgs
Î squark/gluino masses > 2.5 TeV
But most other points covered well
If SUSY exists, prospects at LHC look favorable
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R-Parity Violation
Non-conservation of RP ≡ (-1)3(B-L)+2S leads to
3 new terms in SUSY superpotential:
W = λ ijk Li L j Ekc + λ ijk
′ Qi L j Dkc + λ ijk
′′ Uic Lcj Dkc
Choose most challenging last case of baryon
~0 → 3j
number violation: χ
1
ATLAS Study of “Point 5”
Î m0=100 GeV, m1/2=300 GeV, tanβ=2, µ>0,
A0=300
Î MET is reduced, but still substantial
Î Number of jets increases
Î Leptons from neutralino decays
0.16
0.14
3
10
0.12
Probability
Events/10 GeV/30 fb
-1
Should still be able to explore much of the
parameter space as with mSUGRA
2
10
0.10
0.08
0.06
0.04
0.02
10
0
0
200
400
600
800
1000
ETmiss (GeV)
Figure 20-85 E Tmiss distribution for SUGRA Point 5
in the case of R-parity conservation (shaded histogram) and R-parity violation (empty histogram).
SUSY at the LHC, HCP 2002
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0
2
4
6
8
10 12 14 16 18 20
Njet
Figure 20-86 Total jet multiplicity ( p Tjet > 15GeV )
distribution for R-parity conservation (shaded) and Rparity violation at SUGRA Point 5. The jets are reconstructed using a topological algorithm based on joining
neighbouring cells.
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