win 05
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WIN 05. Supersymmetry searches at the LHC. Filip Moortgat, CERN. Inclusive signatures: discovery, fast but not unambiguous Exclusive final states & long term measurements: towards understanding the underlying model. - PowerPoint PPT PresentationTRANSCRIPT
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
WIN 05
• Inclusive signatures: discovery, fast but not unambiguous
• Exclusive final states & long term measurements: towards understanding the underlying model
Supersymmetry searches at the LHC
Filip Moortgat, CERN
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Why SUSY is a good idea
One of the most appealing extensions of the Standard Model:
TeV-scale supersymmetry
Solves several problems at once:
• dark matter candidate (e.g. lightest neutralino)• opening towards a theory of gravity• unification of gauge couplings• hierarchy problem• allows to explain why the Higgs mechanism works
[= a symmetry between fermions and bosons, duplicates the SM particle spectrum, but not the couplings]
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
SUSY models
• In general MSSM: many allowed soft SUSY breaking parameters (124) due to unknown nature of SUSY breaking mechanism
= difficult to work with
use more constrained models
• Most popular: mSUGRA
• Also mGMSB, AMSB
m0 , m1/2 , A0 , tan , sign(
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
The Large Hadron Collider
(8 T !!)
yr/fb 100 20
scm10102. L
TeV14:
1-
1-2-3433
spp
also AA and pA collisions; for PbPb : 5.5 TeV/nucleon and L = 1027 cm-2s-1
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Generic SUSY signatures
General characteristics of R-parity conserving SUSY:
• sparticles pair produced and LSP stable large amount of missing transverse energy
• coloured sparticles are copiously produced and cascade down to the LSP with emission of many hard jets and often leptons
Generic SUSY signatures are ET
miss + multi-jets (and multi-leptons)
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Inclusive SUSY
• jets + ETmiss
• 1,2,3 lepton + ETmiss
• opposite sign (OS) or same sign (SS) di-leptons
• often several topologies simultaneously visible
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Jet + MET
Signature: ETmiss + jets
• ~ 1 pb at 1 TeV → physics for startup
• significant reach after 1 yr
• with 300 fb-1, reach squarks and gluinos up to ~ 2.5 TeV
• (need good understanding of detector and backgrounds!)
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Variable that gives information on the “SUSY scale”:
Et sum
SM background
SUSY (700 GeV)
[Branson et al, ATLAS]
Warning: model dependent plot!
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Same-sign dileptons
Lpp gu X 1 d
L
01
1t t1 b
L 01
Signal:
pp tt X W b
Y
W b
Background:
[Drozdetski et al, CMS] ask for 2 SS leptons + hard jets + ETmiss
_
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Exclusive final states
• so far: inclusive measurements fast discovery, but does not unambiguously single out SUSY
• need to reconstruct sparticle decay chains and masses involved need to be prepared for all possible final states
• goal is to measure cross sections, BR’s ( couplings) and even spin of the sparticles LHC can not only discover SUSY, but also MEASURE its properties (if nature is kind)
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Coloured sparticle decays
qqqqg ~,~~)~()~( qmgm Region
1
Region 2, e.g.
bbbbgqgqL ~
,~~,~~
Region 3 )~()~( gmqm qqgqgq ~,~~
[Pape, CMS]
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Neutralino2 decay signatures
01
002 Z
01
02 ll
ll ~0
2
01
002 h
[Pape, CMS]
02q q~
Significant fraction of
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Decay chain to dileptons
g~ q~
q q
02 l
~
l
missTE0
1
l
• 2 high pt isolated leptons• 2 high pt jets• missing Et
Final state:
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Kinematic endpoints
Kinematic endpoint technique: construct lepton/quark upper/lower endpointsand relate them to the masses in the decay chain
E.g.:
4 unknown masses: 4 endpoints:
all masses can be determined
maxmaxmaxmax )(,)2(,)1(,)( llqMqlMqlMllM01
02
,,, ~~ MMMM
lq
q~ q02
01 ~
Usually non-linear relations all masses, not just differencesExtra endpoints, or start from gluino constraints
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Final states with dileptons (1)
M(ll): very sharp end point, triangular shape (due to spinless
slepton)
)1)(1(2~
2
2
2~max
01
02
02
l
lll M
M
M
MMM
%1.0/ MM
[Biglietti et al, ATLAS][Chiorboli et al, CMS]
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Final states with dileptons (2)
M(l1q):
M(l2q):
Can distinguish M(l1q)max from M(l2q)max
M(llq):
)1)(1(2~
2
2~
2
~max2
01
02
lqqql M
M
M
MMM
)1)(1(2
2~
2~
2
~max1
02
02
M
M
M
MMM l
qqql
)1)(1(2
2
2~
2
~max
02
01
02
M
M
M
MMM
qqllq
M(llq)[ATLAS]
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Gluino reconstruction
Choose dilepton pairs close to the edge; then
pMMp )/1( 0
102
~~
can reconstruct and qM ~ qg MM ~~
[Chiorboli et al, CMS]
assuming can be at 01
~02
~rest in the frame of
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Final state with taus
• often decays to taus instead of electrons/muons
• can we use hadronic tau final states?
[Biglietti et al, ATLAS]
endpoint smeared out
02
~
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Decay chain to h0 or Z0
g~ q~
q q
02
missTE0
1
00 , Zh
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Final states with h0 or Z0
Higgs peak can be reconstructed from 2 b-jets
could be a h0 discovery channel !
(even for light H0 and A0)
Z0 reconstructed from di-lepton decay
Decay chain is shorter than for di-leptons
e.g. start from gluinoM(q1h0),M(q2h0),M(qq),M(qqh0)to determine 4 masses
M(bb)
[Paige, ATLAS]
[Moortgat, CMS]h0
A0,H0
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
GMSB signatures
In GMSB, the light gravitino is the LSP
Who is NLSP?
Neutralino is NLSP
Stau is NLSP
ETmiss + , or long-
lived particles
G~0
1
G~~
1
dE/dx and TOF
TOF measurement in the CMS muon DT’s
[Wrochna, CMS]
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
SUSY spin measurement
[Barr, ATLAS]Lq~ L
02 q
~
R
01
)( qlM
qlql and
qlql and
Make use of spin correlations in decay of squark:
no spin correlations
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
SUSY spin measurements (2)
washes out for antisquarks, but in pp colliders more squarks produced than antisquarks
Visible asymmetry: (500 fb-1)
[Barr, ATLAS]
no spin correlations
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Conclusions
• If TeV-scale SUSY exists, its discovery at the LHC should be (relatively) fast, using inclusive signatures
• The LHC can measure sparticle properties: reconstruction of masses in sparticle decay chains, mainly using kinematic endpoints
• Ultimately would like to measure spins and couplings (WIN 05 WINO 5?)
• only 750 days to startup … so focusing on being ready for first day physics now!
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Backup
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Cross sections @ the LHC
“Well known”processes,don’t need to keep all of them …
New Physics!!This we want to keep!!
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
CMS
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
ATLAS
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Civil Engineering
UXC 55
USC 55
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WIN 05, Delphi, Greece, June 2005 Filip Moortgat, CERN
Higgs to sparticles
If accessible, we may exploit the sparticle decay modes:
A, H 20 2
0 4l + ETmiss