GDM scenarios with metastable staus at the LHC

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GDM scenarios with metastable staus at the LHC

• Are R. Raklev
• CERN / University of Bergen
• In collaboration with John Ellis (CERN)
• and Ola Øye (Bergen/ATLAS)

Based on Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Content

• (almost) No motivation
• Gravitino Dark Matter (GDM) models
• Signatures of Massive Metastable Charged
  Particles (MMCPs)
• Fast simulation of GDM benchmarks
• Measuring the stau mass
• Reconstructing heavier sparticles
• Some conclusions

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The set of all SUSY models
SUSY
LSP/ Dark Matter Candidates
MSSM
GMSB
CMSSM
NMSSM
Split SUSY
AMSB
NLSP/ Metastable?
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The set of all SUSY models
SUSY
LSP/ Dark Matter Candidates
MSSM
GMSB
CMSSM
NMSSM
Split SUSY
AMSB
NLSP/ Metastable?
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GDM
CMSSM for generic values of
No EWSB
Usually assumes neutralino LSP with standard
signature of missing energy jets (leptons)
Stau LSP
Battaglia et al., hep-ph/0106204
Low scalar mass excluded
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GDM
CMSSM for generic values of
No EWSB
Usually assumes neutralino LSP with standard
signature of missing energy jets (leptons)
With gravitino LSP low scalar mass allowed with
stau NLSP
Stau LSP
Battaglia et al., hep-ph/0106204
?
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GDM
The allowed mSUGRA parameter space, assuming also
the Polonyi model of SUSY-breaking
is a restricted area in the mass-plane with a
long lived stau NLSP
De Roeck, Ellis, Gianotti, Moortgat, Olive,
Pape, hep-ph/0508198
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GDM
For our fast simulation study we have looked at
three benchmark points
De Roeck, Ellis, Gianotti, Moortgat, Olive,
Pape, hep-ph/0508198
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MMCP signatures
Many interesting experimental signatures

• Slow, muon-like particles
• High ionization
• Displaced vertices
• Late decays of trapped particles (Bragg peaks?)
• Charge flipping

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MMCP signatures
Many interesting experimental signatures

• Slow, muon-like particles
• High ionization
• Displaced vertices
• Late decays of trapped particles (Bragg peaks?)
• Charge flipping

However, some challenging problems

• Issues with triggers for slow particles
• Recording complete events

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Fast simulation
Event generation
epsilon
PYTHIA 6.323 CTEQ 5M1
zeta
Cross sections
eta

• Espilon 3.35 pb
• Zeta 23.4 fb
• Eta 24.1 fb

Integrated luminosity

• Espilon 30 fb-1
• Zeta 300 fb-1
• Eta 300 fb-1

Velocity distribution for staus
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Fast simulation
Detector simulation
AcerDET 1.0
Standard setup, staus treated as muons with
momentum resolution
where
Polesello, Rimoldi, ATL-MUON-99-006
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Fast simulation
Detector simulation
AcerDET 1.0
Standard setup, staus treated as muons with
momentum resolution
and velocity resolution
Ambrosanio, Mele, Petrarca, Polesello, Rimoldi,
hep-ph/0010081
Polesello, Rimoldi, ATL-MUON-99-006
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An mSUGRA event at the LHC
One usually looks at sets of invariants
E.g.
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A GDM event at the LHC
In principle, complete reconstruction of
sparticles possible starting from stau.
Large branching ratio to taus
Neutralino reconstructed from stau-tau pairs and
we can continue up the chain...
However, first we need to trigger on SUSY events
and to remove SM background...
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Trigger
Fast sim. uses ATLAS TDR high luminosity trigger
thresholds, using only jet and muon triggers and
staus with
The resulting trigger efficiencies are still well
above 90
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Background
Many of the usual techniques for isolating SUSY
events apply, however in addition
A pair of high momentum, slow muons!
Backgrounds simulated Zjet, Wjet, WW/WZ/ZZ,
QCD and ttbar
CMS collaboration
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Stau mass
Stau mass can potentially be measured down to
0.1 accuracy!
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Stau mass
However, results depend on parametrization and
lowest velocity!
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Neutralino mass
Neutralino has large branching ratio to stau,
Want to reconstruct neutralino, but missing
neutrinos from tau decays
In events with two taus solution is to project
missing momentum on assumed decay products
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Neutralino mass
Neutralino has large branching ratio to stau,
Want to reconstruct neutralino, but missing
neutrinos from tau decays
epsilon
zeta
eta
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Neutralino mass
Neutralino can be reconstructed from stau tau
combinations
epsilon
zeta
eta
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Reconstructing decay chains
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Reconstructing decay chains
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Reconstructing decay chains
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Reconstructing decay chains
Ellis, ARR, Øye, JHEP 0610 (2006) 061
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Conclusions

• MMCPs have generic signatures that should be easy
  to spot at the LHC, however
• a good understanding of trigger and event
  recording with slow particles in the detectors is
  needed to reach the full LHC potential
• further full simulation of detectors needed to
  understand and improve measurement of MMCP
  velocity
• SUSY masses in models with MMCPs should be
  measurable to high precision, in particular the
  MMCP mass with an expected accuracy at the
  per-mille level

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Process dependence
Drell-Yan
Neutralino/chargino
Other SUSY
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mSUGRA?
The MSSM has four types of SUSY-breaking
parameters
mSUGRA
Nilles, 1984
mSUGRA
CMSSM
EWSB fixes
EWSB fixes