The CBM experiment at FAIR

1
The CBM experiment at FAIR

• Claudia Höhne, GSI Darmstadt
• CBM collaboration

• Outline
• motivation, physics case
• observables
• experiment
• feasibility studies
• dileptons ee- ? mm- ?

2
CBM

• Compressed Baryonic Matter experiment
• SIS 300 ? U92 15-35 GeV/nucleon with beam
  intensities up to 109/s
• Z/A 0.5 nuclei up to 45 GeV/nucleon

? exploration of the QCD phase diagram with
heavy-ion collisions! ? investigation of nuclear
matter at highest baryon densities but still
moderate temperatures in AA collisions
3
CBM physics case

• milestone in mapping the QCD phase diagram would
  be the (unambiguous) discovery of either the
  critical point or the 1st order phase transition
• top SPS, RHIC, LHC
• high T, low mB region
• most probably crossover
• high mB region !
• onset of deconfinement?
• 1st order phase transition?
• critical point?
• high baryon density!
• in medium modifications of hadrons
• lower SPS, AGS
• limited in observables, statistics

critical endpoint Z.Fodor, S.Katz, JHEP
0404050 (2004) S.Ejiri et al., hep-lat/0312006
? SIS 300 _at_ FAIR 2nd generation experiment!
? charm, dileptons, fluctuations, correlations
4
Dense baryonic matter

• baryon density in central cell (AuAu, b0 fm)
  in transport calculations HSD (mean field,
  hadrons resonances strings), QGSM similar
  results
• enormous energy and baryon densities reached! (e
  gt ecrit)

CBM physics group, C. Fuchs priv. com.
5
Phase diagram

• UrQMD calculation of T, mB as function of
  reaction time
• (open symbols nonequilibrium,
• full symbols appr. pressure equilibrium)
• phase border crossed already at rather low
  energies
• (see also results from 3-fluid hydrodynamics)
• critical point in reach?

CBM energy range 15 - 35 AGeV for AuAu
Bratkovskaya et al., PRC 69 (2004) 054907
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High baryon density matter!

• hadronic properties should be effected by the
  enormous baryon densities which will be created
• (partial) restoration of chiral symmetry?

Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1,
hep-ph/9909229
Mishra et al ., PRC 69, 015202 (2004)
r
D
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Physics of CBM
CBM rare probes ? high interaction rates!
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Strangeness production

• deconfinement

NA49, C.Blume et al., nucl-ex/0409008

• s-production mechanism different in hadronic /
  partonic scenario
• maximum of strangeness production at 30 AGeV
• ? change from hadronic to partonic phase?
• CBM energy range
• 15 35/45 AGeV (depending on A)
• verify and extend energy dependence!

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Transverse-mass spectra

• deconfinement

energy dependence of ?mt? changes at lower SPS
energies
seen for pions, kaons, protons and their
antiparticles
filled symbol particle open symbol antiparticle
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J/y suppression
deconfinement
E. Scomparin for NA 60, QM05

• screening of cc pairs in partonic phase
• anomalous J/y suppression observed at top-SPS
  and RHIC energies
• signal of deconfinement?
• energy dependence?!

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collective flow
deconfinement

• collapse elliptic flow of protons at lower
  energies signal for first order phase
  transition?! e.g. Stoecker,
  NPA 750 (2005) 121, E. Shuryak, hep-ph/0504048
• full energy dependence needed!

NA49, PRC68, 034903 (2003)
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K/p fluctuations

• Critical point

C.Roland et al., nucl-ex/0403035 S. Das, SQM06

• dynamical fluctuations of the K/p ratio increase
  towards lower energies
• not reproduced by UrQMD resonance contribution?
  
• acceptance effects?
• ? Energy dependence needed also for lower
  energies!

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In medium effects Dileptons

• dileptons are penetrating probes!
• modifications in hot and dense matter expected
  
• see CERES, NA50, NA60, HADES

best way to measure? ee- ? mm-
Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1,
hep-ph/9909229
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modifications ? ? ? ? ll-

• In medium

• high quality data at low and high energies now
  coming in from NA60 (SPS, 158 AGeV, InIn) and
  HADES (SIS, 2 AGeV, CC)
• enhancement of low-mass dilepton pairs!

R. Holzmann for HADES, QM05
E. Scomparin for NA 60, QM05
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modifications ? ? ? ? ee-
In medium
CERES
Phys. Rev. Lett. 91, 042301 (2003)

• intermediate energies with highest baryon
  densities?
• pioneering measurement of CERES
• study full energy dependence!

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D-mesons
In medium
W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl.
Phys. A 691 (2001) 745
D-mesons sensitive to medium!
SIS100/ 300
SIS18
Mishra et al ., PRC 69, 015202 (2004)
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D-mesons (II)
In medium

• Dropping D-meson masses with increasing light
  quark density
• might give a large enhancement of the open
  charm yield at 25 A GeV !

E. Bratkovskaya, W. Cassing, private
communication
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detector requirements
observables
detector requirements challenges
Systematic investigations AA collisions from 8
to 45 (35) AGeV, Z/A0.5 (0.4) (up to 8 AGeV
HADES) pA and pp collisions from 8 to 90 GeV
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The CBM experiment

• tracking, momentum determination, vertex
  reconstruction radiation hard silicon
  pixel/strip detectors (STS) in a magnetic dipole
  field
• electron ID RICH TRD ( ECAL)
• ? p suppression ? 104
• hadron ID TOF ( RICH)
• photons, p0, m ECAL
• high speed DAQ and trigger
• not necessarily fixed layout!
• more like facility

STS
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STS tracking

• task
• track reconstruction for tracks with 0.1 GeV/c lt
  p ? 10-12 GeV/c and with a momentum resolution of
  order 1 at 1 GeV/c
• primary and secondary vertex reconstruction
  (resolution ? 50 mm)
• V0 track pattern recognition (hyperons, ee-
  pairs from g-conversion)

Challenge high track density ? 600 charged
particles in ? 25o
D ? ppK- (ct 317 mm) D0 ? K-p (ct 124 mm)
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STS tracking (II)

• set of silicon tracking stations inside magnetic
  field (heart of CBM)
• 2-3 vertex detectors with high resolution,
  minimum thickness (e.g. MAPS)
• 2-3 pixel detectors for tracking seeds
• outer stations Si-strip
• challenge readout speed (10 MHz interaction
  rate), radiation hardness (109 ions/s),
• material budget, resolution

optimization of layout is ongoing work robust
tracking!!
so far simple standard layout with 7/8 stations
(3 4)/ (224) in use
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Open charm production

• D0 ? K-p (ct 124 mm), minimum bias AuAu
  collisions at 25 AGeV
• ltD0gt 4 10-5
• 50 mm secondary vertex resolution
• proton identification via TOF
• even better signal for
• D ? K-pp
• (3-particle 2nd vertex)

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Hyperons

• identification via 2nd vertices in the STS, no
  hadron ID
• acceptance L (17 ), X (6.5 ) W (7.5 )
• current reconstruction efficiency
• L (56 ), X (26 ) W (36 )
• ? optimize/ improve 2nd vertex finder, STS layout

L
L
? 0.85 MeV
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Hadron identification TOF (RPC)
Squared mass measured with TOF

• challenge counting rate, large area, sufficient
  position resolution, time resolution lt 80ps
• simulations
• central AuAu at 25 AGeV, UrQMD
• time resolution 80ps, TOF wall in 10m distance
  to target
• no track reconstruction and mismatch yet!

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Dynamical fluctuations

• UrQMD central AuAu collisions at 25 AGeV, no
  track reconstruction

4 ? acceptance identified particles
K/ ? 3.2 ? 0.3 2.6 ? 0.6
p/ ? -5.3 ? 0.07 -5.9 ? 0.1

• resonance contribution?!
• little influence of limited detector acceptance
• lower detectable limit of dyn. fluctuations?

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Dileptons

• dileptons are penetrating probes!
• modifications in hot and dense matter expected
  
• see CERES, NA50, NA60, HADES

best way to measure? ee- ? mm-
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Dileptons electrons ? muons
HSD in-medium modifications of low-mass vector
mesons in ee- channel and mm- channel are very
similar! important mass region from 0.2 0.7
GeV/c2 (below under vivid discussion)
E. Bratkovskaya, priv. com.
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Dileptons - electrons
Conceptional studies MC tracks, ideal particle
ID Major background sources p0 ? ? ee-, ?
? ee-
N/event Decay BR
? 36 ? e e- ? 5.10-3
? 38 ? e e- ?0 ? e e- 5.910-4 7.0710-5
? 1.28 ? e e- 3.110-4
?0 28 ? e e- 4.4410-5
Physical background ? small pair opening
angle ? often one hard, one soft electron
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Dileptons - electrons

• low-mass vector mesons develop sophisticated
  cut strategy
• ? (so far) signal quality mainly limited by
  ability of background rejection
• J/y cut on pt (1GeV) seems sufficient
• so far no track reconstruction, PID included

central AuAu, 25 AGeV
J/??ee-
pt gt100 MeV
?
f
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Modified CBM setup ? dimuons

• for investigation of dimuons study alternative
  CBM setup with active muon absorbers (Fe C
  detector layers) after the STS

• ... move absorbers out for hadron runs

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Dileptons - muons

• first study
• minimum bias AuAu, 25 AGeV
• low efficiency for soft muons ? early cutoff in
  invariant mass spectrum of low-mass vector mesons
• phantastic J/y, even y' should be accessible

J/??µµ-
?
f
?
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Dileptons muons (II)
problems low efficiency for soft muons! ?
accepted phase space shifted to forward
rapidities for low-mass vector mesons
challenging muon detector (high particle
densities!)
r
J/y
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Dileptons muons (III)
preliminary !
ongoing simulations studies momentum dependent
muon identification
optimization of absorbers (material,
thickness, position)
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CBM summary

• CBM offers a very interesting physics program
  studying the QCD phase-diagram
• unique features expected in CBM energy range
  first order phase transition, critical point
• CBM as 2nd generation experiment will be able to
  study rare probes, fluctuations and correlations!

• detector development under way
• increasingly realistic feasibility studies are
  performed
• ? Technical proposal in 2007

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CBM collaboration
CBM Collaboration gt 40 institutions, gt 350
Members
Korea Korea Univ. Seoul Pusan National
Univ. Norway Univ. Bergen Germany Univ.
Heidelberg, Phys. Inst. Univ. HD, Kirchhoff Inst.
Univ. Frankfurt Univ. Kaiserslautern Univ.
Mannheim Univ. Münster FZ Rossendorf GSI
Darmstadt Poland Krakow Univ. Warsaw
Univ. Silesia Univ. Katowice Nucl. Phys. Inst.
Krakow   Portugal LIP Coimbra
Croatia RBI, Zagreb China Wuhan Univ. Hefei
Univ. Cyprus Nikosia Univ.   Czech
Republic CAS, Rez Techn. Univ. Prague France
IReS Strasbourg Hungaria KFKI Budapest Eötvös
Univ. Budapest India VECC Kolkata IOP
Bhubaneswar Univ. Chandighar Univ. Varanasi
Romania NIPNE Bucharest Russia IHEP
Protvino INR Troitzk ITEP Moscow KRI, St.
Petersburg Kurchatov Inst., Moscow LHE, JINR
Dubna LPP, JINR Dubna LIT, JINR Dubna MEPHI
Moscow Obninsk State Univ. PNPI Gatchina SINP,
Moscow State Univ. St. Petersburg Polytec.
U. Ukraine Shevshenko Univ. , Kiev to be
approved by CB