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

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Why SUSY is a good idea
One of the most appealing extensions of the
Standard Model
TeV-scale supersymmetry
a symmetry between fermions and bosons,
duplicates the SM particle spectrum, but not the
couplings
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

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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 b , sign(m)
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The Large Hadron Collider
(8 T !!)
also AA and pA collisions for PbPb 5.5
TeV/nucleon and L 1027 cm-2s-1
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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 ETmiss multi-jets
(and multi-leptons)
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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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Jet MET

• Signature ETmiss jets
• s 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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Et sum
Branson et al, ATLAS
Variable that gives information on the SUSY
scale
SM background
SUSY (700 GeV)
Warning model dependent plot!
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Same-sign dileptons
Signal
Background
_
? ask for 2 SS leptons hard jets ETmiss
Drozdetski et al, CMS
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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, BRs (?
  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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Coloured sparticle decays
Pape, CMS
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Neutralino2 decay signatures
Significant fraction of
Pape, CMS
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Decay chain to dileptons

• 2 high pt isolated leptons
• 2 high pt jets
• missing Et

Final state
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Kinematic endpoints
Kinematic endpoint technique construct
lepton/quark upper/lower endpoints and relate
them to the masses in the decay chain
E.g. 4 unknown masses 4 endpoints ?
all masses can be determined
Usually non-linear relations ? all masses, not
just differences Extra endpoints, or start from
gluino ? constraints
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Final states with dileptons (1)

• M(ll) very sharp end point,
• triangular shape (due to spinless
  slepton)
• ?

Biglietti et al, ATLAS
Chiorboli et al, CMS
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Final states with dileptons (2)

• M(l1q)
• M(l2q)
• ?Can distinguish M(l1q)max from M(l2q)max
• M(llq)

M(llq)
ATLAS
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Gluino reconstruction
Choose dilepton pairs close to the edge then
assuming can be at
rest in the frame of
? can reconstruct and
Chiorboli et al, CMS
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Final state with taus

• often decays to taus instead of
  electrons/muons
• can we use hadronic tau final states?

endpoint smeared out
Biglietti et al, ATLAS
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Decay chain to h0 or Z0
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Final states with h0 or Z0
Paige, ATLAS

• 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 gluino
• M(q1h0),M(q2h0),M(qq),M(qqh0)
• to determine 4 masses

M(bb)
Moortgat, CMS
h0
A0,H0
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GMSB signatures

• In GMSB, the light gravitino is the LSP
• Who is NLSP?
• Neutralino is NLSP
• Stau is NLSP
• ? ETmiss ? , ? or long-lived particles

TOF measurement in the CMS muon DTs
Wrochna, CMS
? dE/dx and TOF
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SUSY spin measurement
Make use of spin correlations in decay of squark
Barr, ATLAS
no spin correlations
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SUSY spin measurements (2)
washes out for antisquarks, but in pp colliders
? more squarks produced than antisquarks
Barr, ATLAS

• Visible asymmetry
• (500 fb-1)

no spin correlations
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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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Backup
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Cross sections _at_ the LHC
Well knownprocesses, dont need to keep all of
them
New Physics!! This we want to keep!!
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CMS
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ATLAS
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Civil Engineering
USC 55
UXC 55
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End points and configurations
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Higgs to sparticles
If accessible, we may exploit the sparticle decay
modes
A, H ? ?20 ?20 ? 4l ETmiss