The CBM Experiment at FAIR

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The CBM Experiment at FAIR
International Workshop The Physics of Compressed
Baryonic Matter GSI, December 15-16, 2005
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The CBM Experiment
Tracking STS, TRD Vertexing STS Hadron ID
TOF Electron ID RICH, TRD, ECAL ?, n ECAL
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Conditions for CBM

• Heavy-ion beams up to 35 AGeV
• Light ion beams up to 45 AGeV
• proton beam up to 90 GeV
• Ion beam intensity 109/s!

Access to rarest probes charm near threshold,
low-mass dielectrons Huge experimental
challenges Detection and read-out
speed Radiation hardness Precision rate
capability fast online event processing
Detector RD under way
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Physics topics
deconfinement at high ?B
strangeness (K, ?, S, ?, O) charm (J/?, D) flow
in-medium properties of hadrons
?, ?, f ? ee- open charm
critical point
fluctuations
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Observables
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CBM Feasibility Studies

• D0?pK- (D?ppK)
• J/??ee-
• J/??µµ-
• ?,?,f?ee-
• ??p-p, ?-??p-, O-??K-
• K/p fluctuations

• Simulation levels
• pure Monte-Carlo (principal feasibility
  acceptance, estimated yields)
• anticipated detector response, track and vertex
  reconstruction
• full detector simulation including global
  tracking and PID

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Performance of STS for D0 Mesons
invariant pK- mass
vertex resolution
without PID
similar studies for D (larger ct, better vertex,
3-particle combinatorics)
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Open Charm Questions
What should me measure yields, spectra,
flow? How close to threshold do we have to
go? What about charmed baryons? (?c, t 60 µm,
very challenging!)
Huge impact on design of STS!
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The Silicon Tracking System
"minimal setup" 3 pixel stations 4 strip
stations
Critical issues matgerial budget precision radiat
ion hardness speed
momentum resolution lt 1
alternative options (including hybrid pixels for
track seed) under investigation
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Charmonium
Electrons identified in TRD ( RiCH) Signal
extraction straightforward Requires pion
suppression gt 103 Requires highest beam
intensities
J/?
1010 events
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Low-mass Dielectrons
ee- sources
Main background sources pion Dalitz, ?
conversion Requires sophisticated rejection
strategy
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Low-mass Dielectrons (ctd.)
S/B about 1 for ?,f small for low-mass
continuum requires good modelling of
combinatorial background pion rejection better
than 103 reduced magnetic field
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K/p Fluctuations
4 ? acceptance(UrQMD) identified particles
K/ ? 3.2 ? 0.3 2.6 ? 0.6
p/ ? -5.3 ? 0.07 -5.9 ? 0.1
Acceptance and kaon ID seems suited for
fluctuation measurement
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The Muon Option
Combination of carbon and iron absorbers with
detectors
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The Muon Option J/?
seems to work well for fast muons from charmonium
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The Muon Option Low-mass Vector Mesons
?
reasonable for mesons with vacuum masses low-mass
continuum not covered further optimisation ongoing
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Conclusions so far

• CBM seems conceptually to be able to measure the
  desiredobservables, provided the required
  detector performances can be reached.
• Different observables require
• different running conditions
• highest interaction rate (107/s), highly
  triggered charm
• untriggered (several 104/s) all others
• modified setups low-mass dielectrons
• target position
• magnetic field
• different setup muons

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Summary

• Feasibility studies show that CBM is conceptually
  able to measure its key observables provide the
  design performance is reached.
• Detector RD is under way to meet the unprecented
  requirements.
• This will open up a new domain of observables not
  measured before at FAIR energies or in heavy-ion
  reactions at all.
• To improve our knowledge of QCD with CBM, we need
  quantitative predictions from theory, such that
  data can rule out or confirm scenarios.
• Requirements of theory on measurements of
  observables will have a huge impact on the final
  detector design.
• We would like to have a priority list of
  observables, which are expected to answer key
  questions of theory.

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