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

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 300 @ FAIR 2nd generation experiment! → charm, dileptons, fluctuations, correlations

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.]

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 Au+Au [Bratkovskaya et al., PRC 69 (2004) 054907]

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!

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

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, 015202 (2004) ]

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/9909229]

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

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)

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%

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

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

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

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.]

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)