What the LHC Will Teach Us
About Low Energy
Supersymmetry
Darin Acosta
representing
ATLAS
&
Outline
Introduction to SUSY, LHC, and the Detectors
Trigger strategies at start-up
Inclusive squark/gluino searches
SUSY Spectroscopy
Î Di-lepton edges
Î squark and gluino 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 the total
cross-section for low energy SUSY
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
CMS DAQ Technical
Design Report
CERN/LHCC 2002-26
High lumi
Low lumi
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)
(1 day of running)
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 O(10 Hz)
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Example Trigger Strategy (CMS)
Low luminosity case, L = 2×1033 cm-2s-1
Possible triggers at Level-2
(looser requirements at Level-1):
Î 1 jet ET>180 GeV & MET>120 GeV
Î 4 jets ET>110 GeV
(values at 95% gen. effic.)
Overall efficiencies to pass both trigger levels
for the SUSY points are:
Î ε=0.63, 0.63, 0.37, 0.43, 0.38, 0.23
4
5
6
4R
2nd jet
5R
6R
With RP
1st jet
Background rate of ~12Hz
dominated by QCD
More exclusive triggers involving angular
correlations among objects can be added to
further improve efficiency
Trigger becomes more efficient at high luminosity
since one expects to explore higher masses
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Lepton and Photon Triggers
Differential Rate ( Hz/GeV/c
2
)
Anticipated thresholds by ATLAS and CMS for
an initial luminosity of L = 2×1033 cm-2s-1
Î 1e: PT > 25 GeV
Î 2e: PT > 15 GeV
Î 1µ: PT > 20 GeV
Î 2µ: PT > 10 GeV
Î 1τ: PT > 85 GeV
Î 2τ: PT > 60 GeV
Î 1γ: PT > 60–80 GeV
Î 2γ: PT > 20–40 GeV
10
L = 2x10 33
1
Minimum Bias
Z/ γ* → µ + X
10
10
10
10
CMS
tt→ µ+X
-1
-2
-3
-4
0
20
40
60
80
100
120
140
160 180 200
2
µµ
M inv
( GeV /c )
Di-muon invariant
mass at Level-3
Sufficient handle on
muon trigger rate:
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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 sparticle 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:
Common cuts:
Î MET>200 GeV, ≥2 jets, ETjet > 40 GeV, |η|<3
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.
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
Î Opposite-sign leptons useful for sparticle recon.
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)
~1 year
@ L=1034
1000
~
~
2
q(
q(2
50
000
0)
)
TH
~
g(2000)
miss
ET
800
-1
(10 fb )
~1 year
@ L=1033
~
g(1500)
600
~
miss
1
q(
0)
50
2
h =1
2
4
h = 0.
ET
-1
(1 fb )
~1 month
@L=1033
~
400
g(1000)
0)
00
~
q(1
~
5
0.1
2
h =
~1 week
@L=1033 200
~
q(5
00)
Tevatron
reach
< 0.5 TeV
g(500)
h(110)
(but one
year for
sparticle 0 0
reconstruction)
EX
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
~1 year
@ L=1033
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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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 of baryon number
~0
violation (last case): χ 1 → 3 j
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, Aspen 2003
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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.
D. Acosta, University of Florida
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 (e,µ), 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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Evolution of Di-Lepton Edges
104
m0 = 90 GeV, m1/2 = 220 GeV
m~
χ2o = 164 GeV, me~R= 129 GeV
m~
τ1 = 128 GeV
103
Events / 4 GeV
m0 = 100 GeV, m1/2 = 190 GeV
µ>0, A0 = 0
tanβ = 2
~0
χ
2
103
m~
χ2o = 140 GeV, me~R= 132 GeV
mτ1 = 124 GeV
~
eRe / ~
µR µ
ee,µµ
ee,µµ
~0
χ
2
~
~
eRe / µRµ
~0 ~
χ
τ1 τ
2
102
5 fb-1
102
µ>0, A0 = 0
tanβ = 10
5 fb-1
eµ
eµ
10
10
SM
SM
1
0
1
100
200
+
M(I I ) (GeV)
103
300
100
200
M(I+I-) (GeV)
0
103
m0 = 90 GeV, m1/2 = 220 GeV
µ>0, A0 = 0
tanβ = 20
m~
χ20 = 167 GeV, me~R= 132 GeV
m~
τ1 = 103 GeV
ee,µµ
102
300
m0 = 100 GeV, m1/2 = 190 GeV
µ>0, A0 = 0
tanβ = 25
102
m~
χ20 = 141 GeV, me~R= 132 GeV
mτ1 = 91 GeV
eµ
5 fb-1
5 fb-1
ee,µµ
eµ
SM
1
0
SM
1
100
200
300
D_D_2017c
10
10
0
M(I+I-) (GeV)
100
200
M(I+I-) (GeV)
300
Î SUSY may reveal itself early through
peculiarities in the the di-lepton spectra
Î Structures tend to be less evident with
~0 → χ
~ 0τ +τ − dominates
increasing tanβ, where χ
2
1
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Di-Tau Edge Reconstruction
ATLAS Physics TDR study (Full GEANT simulation)
to select hadronic tau decays
Î Select narrow isolated jets: Rjet=0.2, Riso=0.4
Î Require 0.8 GeV < Mjet < 3.6 GeV
Î Biased against 1-prong decays, but improves
Mττ resolution (less neutrino momentum)
Î Di-tau efficiency is 41%
Î Mvis = 0.66 Mττ
Additional event selection cuts
Î 4 jets: ET1 > 100 GeV, ET2-4 > 50 GeV,
Î MET>100 GeV, no e,µ leptons with pT>20 GeV
ATLAS “Point 6”:
m0=200GeV m1/2=200GeV
tanβ=45 µ<0 A0=0
d
Real τ from SUSY
L=30 fb–1
Events/2.4 GeV/10 fb-1
i
~ 0 → ττ
~ = 99.9%
BR χ
2
Fake τ from SUSY
SM background
1000
500
0
0
25
50
75
Mττ (GeV)
SUSY at the LHC, Aspen 2003
100
20
Mvis = 40 GeV
Expected edge = 60 GeV
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Exclusive Sparticle Reconstruction
Completely reconstruct a SUSY decay chain:
p
l
b
m
~
χ 20
~
g
~±
l
~
b
p
ATLAS Study
~
χ10
l±
b
~
q
~~, qq
~~, gg
~~ dominate)
( qg
Î “Point 3” of Physics TDR
Îm0=200 GeV, m1/2=100 GeV, tanβ=2, µ<0, A0=0
CMS Study [Chiorboli]
Î Investigate Points B & G of “Proposed Post-LEP
Benchmarks for SUSY” (hep-ph/0106204)
ÎB: m0=100 GeV, m1/2=250 GeV, tanβ=10, µ>0, A0=0
– σTOT(SUSY) = 58 pb
ÎG: m0=120 GeV, m1/2=375 GeV, tanβ=20, µ>0, A0=0
– σTOT(SUSY) = 6.0 pb
Î ISASUGRA→PYTHIA→CMSJET
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Di-Lepton Edge Reconstruction
p
l
b
~
χ 20
~
g
~±
l
~
b
BR=16%
l±
b
~
q
p
~
χ10
m
~ 0 (tanβ not too large)
Start with reconstructing χ
2
900
800
Point B
Events / 2 GeV
Events / 3 GeV
Î Two OS isolated leptons, PT>15 GeV, |η|<2.4
Î
MET>150 GeV, E(ll)>100 GeV
SUSY
-
tt
700
Subtract
opposite
flavors
Edge=
79±2 GeV
50
Z + jet
600
40
L=10 fb–1
CMS
500
400
30
300
20
200
10
100
0
0
25
50
75
100 125 150 175 200
0
M(e e )+M(µ µ ) (GeV)
+ -
+ -
0
20
40
60
80
100
120
140
160
180
200
M(e+e-)+M(µ+µ-)-M(e+µ-)-M(µ+e-) (GeV)
Select 15 GeV window around di-lepton endpoint
~0
~0
Î χ 1 at rest in χ 2 rest frame
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 Point B: 174 GeV,
F
d i GH
~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
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~
b Reconstruction
p
b
~
χ 20
~
g
~±
l
~
b
p
~
χ10
lm
l±
b
~
q
BR ~ 5%
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
Require
Î MET>150 GeV
Î E(ll)>100 GeV
Point B
Events / 28 GeV
Result of fit:
~ = 500±7 GeV
M(b)
σM = 42 GeV
35
30
-
tt
P1
P2
P3
P4
P5
P6
P7
P8
L=10 fb–1
CMS
25
20
Generated masses:
~ ) = 496 GeV
M(b
ID
Entries
Mean
RMS
SUSY
103
291
504.6
152.8
25.38 / 20
0.3074E-13
-0.1512E+16
0.2550E+13
0.2699E+11
-0.6571E-02
25.57
500.1
42.22
15
10
L
~
M(bR) = 524 GeV
5
0
0
200
σ × BR dominates
SUSY at the LHC, Aspen 2003
23
400
600
800
M(
1000
0
2
b) (GeV)
Mass (GeV)
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~
g Reconstruction
p
b
~
χ 20
~
g
~±
l
~
b
l±
BR ~ 1%
b
~
q
p
~
χ10
lm
Add another b-jet closest in φ to reconstruct g~
~
& 400 GeV < M b < 600 GeV
Events / 28 GeV
ch
Result of fit:
~
M(g) = 594±7 GeV
σM = 42 GeV
SUSY
30
203
153
626.7
91.15
12.39 / 10
0.1430E-12
0.1678E+15
-0.5078E+14
0.1170E+12
-0.9486E-02
19.45
593.5
42.37
ID
Entries
Mean
RMS
35
-
tt
P1
P2
P3
P4
P5
P6
P7
P8
CMS
L=10 fb–1
Point B
25
20
15
10
Generated mass:
~ = 595 GeV
M(g)
5
0
af ch
200
300
400
500
d i
30
Entries
124
8.681 / 7
-0.2030E-09
-0.2055E+09
0.1989E+08
-0.1692E+08
-0.2288E-01
27.32
92.41
16.91
P1
P2
P3
P4
P5
P6
P7
P8
25
SUSY
-
tt
Expect 87 GeV
10
900
0
2
1000
b b) (GeV)
Mass (GeV)
ATLAS Point 3
20
15
800
20000
Events/4 GeV/10 fb-1
Events / 15 GeV
Point B
CMS
700
M(
~0 :
~ − m b~ is independent of m χ
Îm g
1
35
600
Expect 20 GeV
15000
10000
5000
5
0
0
50
100
150
200
M(
250
0
2
b b) - M(
0
300
0
2
b) (GeV)
Mass (GeV)
SUSY at the LHC, Aspen 2003
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0
20
40
60
M(χ2bb)-M(χ2b) GeV
80
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100
~
q Reconstruction
BR ~ 5%
q
Same di-lepton edge selection as before
Two jets with pT>20 GeV, |η|<2.4
MET > 100 GeV
Veto all b-jets
Î Track with second largest IP significance < 2σ
Î Helps reject sbottom and stop decays
Less luminosity required (1 fb-1)
Result of fit:
~
M(q) = 536±10 GeV
σM = 60 GeV
CMS
L=1 fb–1
Point B
Generated masses:
~ ) = 543 GeV
M(q
L
~
M(qR) = 537 GeV
Mass (GeV)
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Point G Reconstruction
Cross section 10× smaller
Smaller branching ratios
Require 300 fb-1
>1 year @ 1034
Î Eb-jet>350 GeV, MET>350 GeV
ID
Entries
Mean
RMS
14
P1
P2
P3
P4
P5
P6
P7
P8
12
10
8
Result of fit:
~
M(b) = 720 ±26 GeV
σM = 81 GeV
101
89
739.9
206.3
10.13 / 9
0.3413E-12
0.3982E+14
-0.9041E+12
0.2531E+10
-0.5623E-02
9.488
719.7
81.06
Generated masses:
~
M(bL) = 702 GeV
~
M(bR) = 748 GeV
6
4
2
0
400
600
800
1000
1200
Result of fit:
~
M(g) = 850±40 GeV
σM = 130 GeV
gluino
1400
M(
0
2
b) (GeV)
Events / 60 GeV
Events / 60 GeV
sbottom
ID
Entries
Mean
RMS
25
P1
P2
P3
P4
P5
P6
P7
P8
20
15
201
112
898.4
141.6
9.009 / 4
0.6774E-13
0.3944E+16
-0.7096E+14
0.1002E+12
-0.6384E-02
13.08
852.7
130.6
10
Generated mass:
~ = 860 GeV
M(g)
5
0
400
600
800
1000
M(
SUSY at the LHC, Aspen 2003
26
1200
0
2
1400
b b) (GeV)
D. Acosta, University of Florida
Can mSUGRA Escape LHC?
M.Battaglia et al., Eur.Phys.J. C22 (2001) 535
(hep-ph/0106204) 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
X
Sparticles
reconstructed
in 10 fb-1
X
Di-lepton
Sparticles
reconstructed edge not
observable
in 300 fb-1
If SUSY exists, prospects at LHC look favorable
SUSY at the LHC, Aspen 2003
27
D. Acosta, University of Florida
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 mass relations
Possibility to reconstruct squark/gluino/neutralino
decays in mSUGRA for several prototype analyses
Î Mass resolution <10% under some assumptions
Î Generally require tanβ<35
Î Generally require much more data (years)
Trigger strategies identified for efficient coverage
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 !
SUSY at the LHC, Aspen 2003
28
D. Acosta, University of Florida
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
SUSY at the LHC, Aspen 2003
29
D. Acosta, University of Florida
~
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
particles / 20 GeV
CMS:
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:
n=3, tanβ=45,
CMS CR 1999/019
ATLAS
Λ=50-300
TeV,
70
114GeV; L=1/fb; eff=5%
M/Λ=200
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)
SUSY at the LHC, Aspen 2003
30
D. Acosta, University of Florida
~
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
SUSY at the LHC, Aspen 2003
1
10
31
10
2
10
3
cτ (m)
D. Acosta, University of Florida