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The CBM Experiment at FAIR

The CBM Experiment at FAIR. Volker Friese v.friese@gsi.de. CPOD 2007 GSI, 13 July 2007. The FAIR Facility at GSI. 2 x 10 9 /s 238 U 35 GeV/u (Ni: 45 GeV/u) 10 13 /s protons 90 GeV Unique possibility to study extremely rare probes in heavy-ion collisions. First beam on CBM target: 2015.

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The CBM Experiment at FAIR

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  1. The CBM Experimentat FAIR Volker Friese v.friese@gsi.de CPOD 2007 GSI, 13 July 2007

  2. The FAIR Facility at GSI 2 x 109/s 238U 35 GeV/u (Ni: 45 GeV/u) 1013/s protons 90 GeV Unique possibility to study extremely rare probes in heavy-ion collisions First beam on CBM target: 2015 Volker Friese

  3. Radiation hardness Fast detectors and eletronics Online event selection CBM Observables and Requirements Hadron ID Strangeness Lepton ID Flow Hyperons High resolution tracking Open charm High resolution vertexing Charmonium Extreme interaction rates Dileptons Large acceptance Fluctuations Volker Friese

  4. The CBM Detector: Overview • Radiation hard Silicon Tracking System in dipole field • Electron ID in RICH+TRD+ECAL • Hadron ID in TOF (RPC) • γ, μ, π in ECAL • High-speed DAQ and trigger system Volker Friese

  5. The CBM Backbone: Main Tracker (STS) Arrangement of silicon detector stations inside magnetic dipole field Large area coverage: strip sensors High occupancy regions: hybrid pixel detectors /small strips Volker Friese

  6. STS: Task and Challenges • Task: • track reconstruction in high track- density environment with high efficiency • Momentum resolution 1 % • Acceptance coverage 2.5 – 27 degrees UrQMD, central Au+Au @ 25 AGeV • Challenges: • high track density: up to 600 charges tracks per event in the acceptance • fast sensor / readout: up to 107 events per second • low mass detector • suitable for fast (online) event reconstruction algorithms Volker Friese

  7. STS: Conceptional Layout z = 50 cm – 100 cm: double sided strip sensors, pitch 60 μm, stereo angle 15 degrees, material budget 200 – 300 μm Si z = 20 cm – 50 cm: hybrid pixel sensorsor small strips other technologies under discussion beam target Volker Friese

  8. readout & cooling readout & cooling STS: Design of Si-Strip Stations • modular design with few (≈ 3) different wavers • connection of sensors by long-ladder technology • readout and cooling outside of acceptance • low-mass cables • occupancy < 5 % Volker Friese

  9. STS: Layout Studies CAD drawing of target / STS region • Ongoing layout and design • studies: • number / position of stations • pixel vs. strip sensors • strip densors: length, pitch, stereo angle • low-mass mechanical support and cabling Volker Friese

  10. CIS 4"280 µm Si STS: R&D GSI-01 Fast self-triggered readout chip n-XYTER in collaboration with DETNI prospect: CBM-XYTER Strip sensor development with CIS Erfurt First test sensor delivered July 2007 Volker Friese

  11. STS: Gaining Expertise • International workshop on • Silicon Detector Systems • GSI, May 2007: • Review of detector concept • Discussion on (alternative) technologies • Strategies for R&D and prototyping Volker Friese

  12. STS: Hit Pattern for Strip Stations Track inpact points Hit pattern Occupancy Large number of fake hits due to projective strip geometry: challenge for track finding Volker Friese

  13. pixels + strips: 97.02 ± 0.09only strips:94.88 ± 0.12 pixels +strips: 92.17 ± 0.14only strips:90.01 ± 0.15 efficiency [%] momentum [GeV/c] Track fit yields required momentum resolution STS: Track Reconstruction • Track finding with Cellular Automaton method • Good efficiency and performance (78 ms per event on CPU for central Au+Au) • Candidate for high level event selection (implementation in cell processors) • Other algorithms (e. g. Hough Transform, suitable for FPGA) also being developed all tracks primary tracks Volker Friese

  14. L X W STS: Performance for Hyperons Detection by weak decay topology with good acceptance and reasonable effiency: 15.8 % 6.7 % 7.7 % Central Au+Au, 25 AGeV Full reconstruction Almost background-free signals No identification of secondaries required Volker Friese

  15. The Big Challenge: Open Charm • CBM measures open charm close to threshold • extremely low multiplicity to be expected (HSD: <D0> = 2 x 10 -4 for central Au+Au @ 25 AGeV) • For discrimination from prompt background detection of the decay vertex with excellent resolution is required (D0: τ = 127 μm) W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl. Phys. A 691 (2001) 745 Volker Friese

  16. The Key to Open Charm: Vertex Detector (MVD) • Challenge: Determine secondary vertices with a precision of 50 μm or better • Requirements: • very low material budget • excellent coordinate resolution • fast readout • radiation hardness • Solution: 2 – 3 thin Si detector layers close to the target (z = 5cm or 10 cm) inside vaccuum vessel Volker Friese

  17. MVD: Preferred Option MAPS • Monolithic Active Pixel Sensors • developed at IPHC Strasbourg • extremely thin (100 – 150 μm) • excellent position resolution (3 – 5 μm) • radiation hardness • readout speed (max. 10 μs) • Possible running scenario: • reduced interaction rate (1 MHz)  tolerable pile-up (10 – 20 events per frame) • exchange first station (diameter 10 cm) periodically Volker Friese

  18. with proton rejection MVD: Performance for D Mesons Open charm performance is the benchmark criterion for the MVD + STS design Study: D0 π+K-, τ=127 μm, central Au+Au @ 25 AGeV, <D0> = 2 x 10-4 First MAPS at z = 10 cm without PID for daughters Volker Friese

  19. MVD: Open Charm Studies • Ongoing studies: • D±ππK, τ = 317 μm • D0K-π+π+π- • Λc+pK-π+, τ = 62 μm Preliminary: Four particle channel for D0 seems to be preferrable (stricter constraint on 4-track vertex wins over 4-particle combinatorics) Volker Friese

  20. Hadrons Identified: The TOF System • Task: • Separate π-K-p over a large rapidity • interval • Requirements: • Location at z = 10 m from target • 2π acceptance needed for flow and fluctuation studies  large area (120 m2) • Timing resolution <≈ 80 ps • Rate capability > 20 kHz/cm2 Volker Friese

  21. TOF: Design and R&D Large area requires RPC detectors Modular design with pad (inner region) and strip (outer region) readout single gap RPC, Coimbra • R&D frontiers: • uniform resolution over large areas • rate capability • R&D in close cooperation with • FOPI and HADES Volker Friese

  22. TOF: Performance Central Au+Au @ 25 AGeV Full reconstruction Time resolution 80 ps Total efficiency vs. momentum (tracking + matching with TOF) K / π separation up to 3.5 GeV, p / K separation up to 8 GeV at efficiencies of 80 % to 90 % Volker Friese

  23. TOF: Acceptance for Hadrons ycm Bulk of hadrons can be identified by TOF Volker Friese

  24. Electron Identification: RICH Serves for electron identification up to 10 GeV Located directly behind STS, outside of the field Optical layout: Vertically separated focal planes, shielded by magnet yokes Volker Friese

  25. RICH: Ring Reconstruction reconstructed ring radius vs. p reconstructed rings in focal plane central Au+Au @ 25 AGeV Hadron blind up to 6 GeV (with N2 radiator) e / π separation up to 12 GeV Volker Friese

  26. RICH: Performance pion suppression electron efficiency • after track reconstruction, ring finding, matching and RICH quality cuts: • electron efficiency 70 % - 80 % • pion suppression ≈ 500 (misidentification due to false ring-track matches) Volker Friese

  27. w/o pt cut on single e Why Electrons: Low-Mass Vector Mesons CBM: Electron ID after spectrometer  + good inv. mass resolution - opening of conversion pairs fight electron background: γ conversion, π0 and ηDalitz decays π0 γe+e-  π0e+e-ηγe+e- ρe+e-  e+e-φe+e- all identified e+e- after all cuts Volker Friese

  28. w/o single – e pt cut LVM: Phase Space Coverage Phase space for ρ after full reconstruction and analysis cuts with single – e pt cut Good coverage in y and pt; w/o single-e pt cut also at low pt and small minv Volker Friese

  29. Further Electron ID: TRD Tasks: electron / hadron separation for p > 1 GeV tracking (connection of STS and TOF) Current design: 4 x 3 layers (radiator + MWPC) Pad readout Volker Friese

  30. TRD: R&D R&D frontiers: rate capability and speed Prototypes already tested at GSI Beam test facility at GSI Design rates (up to 100 kHz/cm2) well in reach Volker Friese

  31. target 25 mm Combined RICH+TRD: Performance for J/ψ target 250 mm combined pion suppression ≈ 10-4 major background source: electrons from conversion in target; can be reduced by thinner target J/ysm = 38 MeV/c2 y' sm = 45 MeV/c2 Excellent performance for J/ψ; with thin target also ψ' in reach Volker Friese

  32. CBM with Muons: MUCH For muon measurements: RICH replaced by absorber – detector system Challenges: first detectors in EM shower tracking through absorber TRD / TOF help to eliminate fake track matches With removed absorber also suited for hadron measurements Volker Friese

  33. MUCH Design 5 Fe absorbers interlayed with 3 detector stations Pad structure of detector layers Volker Friese

  34. Performance for Di-Muons Background sources: mis-identified hadrons (mostly fake matches) μ from π and K decay J/ysm = 22 MeV/c2 y' sm = 33 MeV/c2 Similar S/B as obtained in di-electron channels! Volker Friese

  35. Feasibility studies, including semi-realistic detector response and full event reconstruction demonstrate that the CBM detector concept is suitable for the measurement of the key observables: charm, low-mass dileptons, strangeness Tough detector R&D ahead to reach the design specifications Summary Progress is fast – stay tuned: 2006 http://www.gsi.de/fair/experiments/CBM 2005 2004 Volker Friese

  36. The CBM collaboration China: CCNU Wuhan USTC Hefei Croatia: RBI, Zagreb Russia: IHEP Protvino INR Troitzk ITEP Moscow KRI, St. Petersburg Korea: Korea Univ. Seoul Pusan National Univ. Univ. Mannheim Univ. Münster FZ Rossendorf GSI Darmstadt Norway: Univ. Bergen Cyprus: Nikosia Univ. Hungaria: KFKI Budapest Eötvös Univ. Budapest Kurchatov Inst. Moscow LHE, JINR Dubna LPP, JINR Dubna Czech Republic: CAS, Rez Techn. Univ. Prague France: IPHC Strasbourg Poland: Krakow Univ. Warsaw Univ. Silesia Univ. Katowice Nucl. Phys. Inst. Krakow LIT, JINR Dubna MEPHI Moscow Obninsk State Univ. PNPI Gatchina SINP, Moscow State Univ. St. Petersburg Polytec. U. India: VECC Kolkata SAHA Kolkata IOP Bhubaneswar Univ. Chandigarh Univ. Varanasi IlT Kharagpur Germany: Univ. Heidelberg, Phys. Inst. Univ. HD, Kirchhoff Inst. Univ. Frankfurt Univ. Kaiserslautern Portugal: LIP Coimbra Romania: NIPNE Bucharest Ukraine: Shevchenko Univ. , Kiev 46 institutions ≈ 400 members Volker Friese Strasbourg, September 2006

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