1. 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

2. 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 mB region –
most probably crossover
high mB region !
onset of deconfinement?
1st order phase transition?
critical point?
high baryon density!
lower SPS, AGS:
limited in observables,
statistics
→ SIS FAIR
2nd generation experiment! → charm, dileptons, fluctuations, correlations

3. 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! (e > ecrit)
[CBM physics group, C. Fuchs priv. com.]

4. 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:
AGeV for Au+Au
[Bratkovskaya et al., PRC 69 (2004) ]

5. Physics of CBM rare probes → high interaction rates! physics topics
deconfinement at high rB ?
softening of EOS ?
order of phase transition ?
Critical point ?
in-medium properties of hadrons
 onset of chiral symmetry restoration at high rB
observables
strangeness production: K, L, S, X, W
charm production: J/y, D
flow excitation function
event-by-event fluctuations
r, w, f  e+e-
open charm
rare probes → high interaction rates!

6. 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

7. open charm production
D0 → K-p+ (ct = 124 mm), minimum bias Au+Au collisions at 25 AGeV
<D0> = 4∙ 10-5
~50 mm secondary vertex resolution
proton identification via TOF
even better signal for
D+ → K-p+p+
(3-particle 2nd vertex)
see poster of
I. Vassiliev (HK21.40)
[Mishra et al ., Phys. Rev. C 69, (2004) ]

8. Dileptons dileptons are penetrating probes!
modifications in hot and dense matter expected –
see CERES, NA50, NA60, HADES
best way to measure? e+e- ↔ m+m-
[Rapp, Wambach, Adv. Nucl. Phys. 25 (2000) 1, hep-ph/ ]

9. dileptons - electrons ω φ J/ψ→e+e-
low-mass vector mesons: develop sophisticated cut strategy
J/y: cut on pt (1GeV) seems sufficient
so far no track reconstruction, PID included
see poster of T. Galatyuk (HK 21.10)
central Au+Au, 25 AGeV
J/ψ→e+e-
pt >100 MeV ω φ

10. dileptons - muons ρ ω φ J/ψ→μ+μ-
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 ω φ
see poster of A. Kiseleva (HK 21.43)

11. dynamical fluctuations
UrQMD: central Au+Au collisions at 25 AGeV, no track reconstruction
data
mixed events
4  acceptance
identified
particles
K/ 
3.2  0.3
2.6  0.6
p/ 
-5.3  0.07
-5.9  0.1
see poster of D. Kresan (HK 21.42)
resonance contribution?
little influence of limited detector acceptance
measurement feasible if dyn. fluctuations > 2%

12. 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 J. Heuser HK 32.6
C. Steinle HK 32.7
posters at DPG: T. Galatyuk HK I. Vassiliev HK 21.40
D. Kresan HK A. Kiseleva HK 21.43
M. Hoppe HK E. Cordier HK 21.65
S. Amar-Youcefi HK 21.79

13. CBM Collaboration : 40 institutions, > 350 Members
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
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
Portugal:
LIP Coimbra
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
supported by EU/FP6 HadronPhysics, INTAS

14. multiplicities Au+Au, 25 AGeV Particle Ncentral Nmbias  38 15.2 
1.28
0.512 0 28
9.2
J/y
1.92 ∙ 10-5
7.7 ∙ 10-6 D0
4 ∙ 10-5

15. EOS in dense baryonic matter
strong indications for soft EOS below ~ 3r0 from SIS (subthreshold K+, flow)
... and at 8r0 with e > ecrit ??
consequences?
→ dileptons, charm!?
[W. Weise, Proc. Hirschegg 2001]
[C. Fuchs, priv. com.]

16. 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)