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The Compressed Baryonic Matter experiment at FAIR

The Compressed Baryonic Matter experiment at FAIR. Claudia Höhne, GSI Darmstadt CBM collaboration. Outline motivation, physics case observables experiment feasibility studies. CBM – physics case.

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The Compressed Baryonic Matter experiment at FAIR

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  1. The Compressed Baryonic Matter experiment at FAIR Claudia Höhne, GSI Darmstadt CBM collaboration • Outline • motivation, physics case • observables • experiment • feasibility studies

  2. 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 0404:050 (2004)] [S.Ejiri et al., hep-lat/0312006] → SIS 300 @ 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: 15 - 35 AGeV for Au+Au [Bratkovskaya et al., PRC 69 (2004) 054907]

  5. 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

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

  7. deconfinement Strangeness production [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!

  8. deconfinement Transverse-mass spectra energy dependence of mt changes at lower SPS energies seen for pions, kaons, protons and their antiparticles filled symbol: particle open symbol: antiparticle

  9. 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?!

  10. collective flow central midcentral peripheral • 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)]

  11. Critical point K/p fluctuations [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? •  energy dependence needed for lower energies!

  12. In medium modifications    → l+l- within acceptance • high quality data at low and high energies now coming in from NA60 (SPS, 158 AGeV, In+In) and HADES (SIS, 2 AGeV, C+C) • enhancement of low-mass dilepton pairs! [E. Scomparin for NA 60, QM05] [R. Holzmann for HADES, QM05]

  13. modifications    → e+e- • In medium CERES [Phys. Rev. Lett. 91, 042301 (2003)] • intermediate energies with highest baryon densities? • pioneering measurement of CERES • study full energy dependence!

  14. D-mesons Consequences for charmonium states if DD threshold drops below their mass! • 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) ]

  15. 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]

  16. detector requirements tracking in high track density environment (~ 1000) hadron ID lepton ID myons, photons secondary vertex reconstruction (resolution  50 mm) large statistics: large integrated luminosity: high beam intensity (109 ions/sec.) and duty cycle beam available for several months per year high interaction rates (10 MHz) fast, radiation hard detector efficient trigger strangeness production: K, L, S, X, W charm production: J/y, D flow excitation function rare signals! CBM! r, w, f e+e- open charm event-by-event fluctuations observables detector requirements & challenges Systematic investigations: A+A collisions from 8 to 45 (35) AGeV, Z/A=0.5 (0.4) (up to 8 AGeV: HADES) p+A and p+p collisions from 8 to 90 GeV

  17. 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 • PSD for event characterization • high speed DAQ and trigger • not necessarily fixed layout! • more like „facility“ STS

  18. STS tracking • task • track reconstruction for tracks with 0.1 GeV/c < 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, e+e- pairs from g-conversion) Challenge: high track density  600 charged particles in  25o D+→ p+p+K- (ct = 317 mm) D0 → K-p+ (ct = 124 mm)

  19. STS tracking (II) Hybrids Strip MAPS Ultimate vertex resolution High resolution tracking With large coverage Should deliver unambiguous seeds • 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 for high precision tracking: 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)/ (2+2+4) in use

  20. 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)

  21. 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

  22. Hadron identification – TOF (RPC) Squared mass measured with TOF • challenge: counting rate, large area, sufficient position resolution, time resolution < 80ps • simulations: • central Au+Au at 25 AGeV, UrQMD • time resolution 80ps, TOF wall in 10m distance to target • no track reconstruction and mismatch yet!

  23. Dynamical fluctuations data mixed events • UrQMD: central Au+Au collisions at 25 AGeV, no track reconstruction • resonance contribution?! • little influence of limited detector acceptance • lower detectable limit of dyn. fluctuations?

  24. 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-

  25. Dileptons: electrons ↔ muons HSD: in-medium modifications of low-mass vector mesons in e+e- channel and m+m- channel are very similar! important: mass region from ~ 0.2 – 0.7 GeV/c2 (below under vivid discussion) [E. Bratkovskaya, priv. com.]

  26. Dileptons - electrons reconstructed PID reconstructed no PID track segment 0 cm 15 cm 200 cm no magnetic field constant magnetic field 7.5 kG Conceptional studies: MC tracks, ideal particle ID Major background sources: π0→γ e+e-, γ→ e+e- Physical background:  small pair opening angle  often: one hard, one soft electron

  27. 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 Au+Au, 25 AGeV J/ψ→e+e- pt >100 MeV ω φ

  28. 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

  29. Dileptons - muons • first study: • minimum bias Au+Au, 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/ψ→μ+μ- ρ ω φ

  30. 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

  31. STS R&D  4"280 µm ADC column row Microstrip Sensors Tracking Stations layout studies Monolithic Active Pixel Sensors beam test module design

  32. RICH R&D development of small sized (r=4mm) PMTs with distributed dynode system enhanced UV sensitivity by usage of wavelength shifter films

  33. TRD R&D MWPC (GSI, Dubna) GEM (Dubna)

  34. RPC R&D close collaboration with FOPI ToF upgrade with multi-strip RPCs

  35. ECAL R&D beam test of prototype modules at U70, Protvino, November 2005

  36. PSD R&D first prototype tested at CERN, August 2006 response to p-beam at different beam energies

  37. CBM – summary • CBM offers a very interesting physics program exploring the QCD phase-diagram at highest baryon densities but still moderate temperatures • 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 • exciting physics from ~2015 on!

  38. CBM collaboration CBM Collaboration : 46 institutions, > 400 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 IIT Kharagpur 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

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