The Compressed Baryonic Matter (CBM) experiment at FAIR
Claudia Höhne, GSI Darmstadt
CBM collaboration
Outline
• physics case
• CBM experiment
• feasibility studies of key observables
supported by EU/FP6 HadronPhysics
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Introduction
• 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 B region –
most probably crossover
• high B region !
onset of deconfinement?
1st order phase transition?
critical point?
high baryon density!
• lower SPS, AGS:
limited in observables,
statistics
→ SIS 300 @ FAIR
2nd generation experiment! → charm, dileptons, fluctuations, correlations
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Dense baryonic matter
• baryon density in central cell (Au+Au, b=0 fm) in transport calculations HSD (mean field, hadrons + resonances + strings), QGSM similar results
• enormous energy and baryon densities reached! ( > crit)
[CBM physics group, C. Fuchs priv. com.]
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Phase diagram
[Bratkovskaya et al., PRC 69 (2004) 054907]
• UrQMD calculation of T, B 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 Au+Au
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Physics of CBM
physics topics
deconfinement at high B ?
softening of EOS ?
order of phase transition ?
Critical point ?
in-medium properties of hadrons
onset of chiral symmetry restoration at high B
observables
strangeness production: K,
charm production: J/, D
flow excitation function
event-by-event fluctuations
e+e-
open charm
rare probes → high interaction rates!
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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) suppression 104
• hadron ID: TOF (& RICH)
• photons, 0, : ECAL
• high speed DAQ and trigger
• not necessarily fixed layout!
• more like „facility“
STS
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open charm production• D0 → K-+ (c= 124 m), minimum bias Au+Au collisions at 25 AGeV
• <D0> = 4∙ 10-5
• ~50 m secondary vertex resolution
• proton identification via TOF
• even better signal for D+ → K-++
(3-particle 2nd vertex)
see poster of I. Vassiliev (HK21.40)
[Mishra et al ., Phys. Rev. C 69, 015202 (2004) ]
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Dileptons
[Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1, hep-ph/9909229]
• dileptons are penetrating probes!
• modifications in hot and dense matter expected –
see CERES, NA50, NA60, HADES
best way to measure? e+e- ↔ +-
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dileptons - electrons• low-mass vector mesons: develop sophisticated cut strategy
• J/: cut on pt (1GeV) seems sufficient
• so far no track reconstruction, PID included
see poster of T. Galatyuk (HK 21.10)
J/ψ→e+e-
central Au+Au, 25 AGeV
pt >100 MeV
φω
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dileptons - muons
• study alternative CBM setup with active muon absorbers (Fe + C + detector layers)
• minimum bias Au+Au, 25 AGeV
• low efficiency for soft muons
• challenging muon detectors
J/ψ→μ+μ-
ρ φωsee poster of A. Kiseleva (HK 21.43)
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dynamical fluctuations
4 acceptance identified
particles
K/ 3.2 0.3 2.6 0.6
p/ -5.3 0.07 -5.9 0.1
datamixed events
2 2dyn data mixed
• UrQMD: central Au+Au collisions at 25 AGeV, no track reconstruction
see poster of D. Kresan (HK 21.42)
• resonance contribution?
• little influence of limited detector acceptance
• measurement feasible if dyn. fluctuations > 2%
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CBM status and outlook
• FAIR recently approved by german cabinet
• CBM offers a very interesting physics program
• detector development under way
• increasingly realistic feasibility studies are performed
• open charm measurement well possible
• dilepton spectrum via dielectrons or dimuons?
• particle ratio fluctuations measurable down to ~ 2%
talks at DPG: F. Uhlig HK 13.3 J. Heuser HK 32.6
C. Steinle HK 32.7
posters at DPG: T. Galatyuk HK 21.10 I. Vassiliev HK 21.40
D. Kresan HK 21.42 A. Kiseleva HK 21.43
M. Hoppe HK 21.64 E. Cordier HK 21.65
S. Amar-Youcefi HK 21.79
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CBM collaborationCBM Collaboration : 40 institutions, > 350 Members
Croatia: RBI, Zagreb
China:Wuhan Univ.Hefei Univ.
Cyprus: Nikosia Univ. Czech Republic:CAS, RezTechn. Univ. Prague
France: IReS Strasbourg
Hungaria:KFKI BudapestEötvös Univ. Budapest
India:VECC Kolkata
Romania: NIPNE Bucharest
Russia:IHEP ProtvinoINR TroitzkITEP MoscowKRI, St. PetersburgKurchatov Inst., MoscowLHE, JINR DubnaLPP, JINR DubnaLIT, JINR DubnaMEPHI MoscowObninsk State Univ.PNPI GatchinaSINP, Moscow State Univ. St. Petersburg Polytec. U.
Ukraine: Shevshenko Univ. , Kiev
Korea:Korea Univ. SeoulPusan National Univ.
Norway:Univ. Bergen
Germany: Univ. Heidelberg, Phys. Inst.Univ. HD, Kirchhoff Inst. Univ. FrankfurtUniv. KaiserslauternUniv. Mannheim Univ. MünsterFZ RossendorfGSI Darmstadt
Poland:Krakow Univ.Warsaw Univ.Silesia Univ. Katowice Portugal: LIP Coimbra
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multiplicities
• Au+Au, 25 AGeV
Particle Ncentral Nmbias
38 15.2
1.28 0.512
0 28 9.2
J/ 1.92 ∙ 10-5 7.7 ∙ 10-6
D0 4 ∙ 10-5
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EOS in dense baryonic matter
• strong indications for soft EOS below ~ 30 from SIS (subthreshold K+, flow)
• ... and at 80 with > crit ??
• consequences? → dileptons, charm!?
[C. Fuchs, priv. com.]
[W. Weise, Proc. Hirschegg 2001]
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Feasibility studies
• study feasibility of measurement of key observables by means of full scale simulations of the CBM detector and event reconstruction
• tracking efficiency and momentum resolution in STS (2 MAPS, 1 hybrid pixel, 4 strip detectors)