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Physics goals and status of feasibility studies of the CBM experiment

Physics goals and status of feasibility studies of the CBM experiment. Claudia Höhne GSI Darmstadt, Germany. Outline. motivation for CBM physics topics high baryon densities (  in medium properties of hadrons ) deconfinement critical point CBM detector

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Physics goals and status of feasibility studies of the CBM experiment

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  1. Physics goals and status of feasibility studies of the CBM experiment Claudia Höhne GSI Darmstadt, Germany

  2. Outline • motivation for CBM • physics topics • high baryon densities ( in medium properties of hadrons) • deconfinement • critical point • CBM detector • feasibility studies (special emphasis on TRD) • tracking • fluctuations • J/y, low mass vector mesons • D-mesons • outlook

  3. critical endpoint: [Z.Fodor, S.Katz, JHEP 0404:050 (2004)] [S.Ejiri et al., hep-lat/0312006] Motivation Mapping the QCD phase diagram of strongly interacting matter with heavy ion collisions • high T, low mB •  top SPS, RHIC, LHC • low T, high mB •  SIS • intermediate range ?  low energy runs SPS, AGS limited in observables, statistics  SIS 300 @ GSI ! • 2nd generation experiment needed! • Highest baryon densities! • → in medium properties of hadrons • Deconfinement? • Critical point? SIS100/300

  4. TRD ! physics topics observables deconfinement at high rB ? softening of EOS ? strangeness production: K, L, S, X, W charm production: J/y, D flow excitation function  PID! 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 Physics topics and observables

  5. 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 • CBM energy range: • 15 – 35/45 AGeV (depending on A) • verify and extend energy dependence!

  6. Deconfinement: J/y suppression [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?!

  7. Deconfinement: charm production Predictions of open charm yield for central A+A collisions differ by orders of magnitude for different production scenarios, especially at low energies  D-meson, J/y [Gorenstein et al J. Phys. G 28 (2002) 2151] central Au+Au

  8. central midcentral peripheral Deconfinement: collective flow • collapse of v1 and v2 flow of protons at lower energies signal for first order phase transition?! • full energy dependence needed! [NA49, PRC68, 034903 (2003)]

  9. within acceptance In medium modifications:    → l+l- • 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]

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

  11. D-mesons in medium [W. Cassing, E. Bratkovskaya, A. Sibirtsev, Nucl. Phys. A 691 (2001) 745] SIS100/ 300 SIS18

  12. D-mesons in medium (II) various QCD inspired models predict a change of the D-mass in a hadronic medium [Mishra et al ., Phys. Rev. C 69, 015202 (2004) ] • in analogy to kaon mass modification, but drop for both, D+ and D- • substantial change (several 100 MeV) already at =0 • effect for charmonium is substantially smaller

  13. D-mesons in medium  J/y Consequence of reduced D mass: DD threshold drops below charmonium states [Mishra et al., Phys. Rev. C 69, 015202 (2004) ] • decay channels into DD open for ’, c, J/y • broadening of charmonium states • suppression of J/y  lepton pair channel (large fraction of J/y from higher states) • (slight) enhancement of D mesons

  14. Critical point: fluctuations [C.Roland et al., nucl-ex/0403035] • dynamical fluctuations of the K/p ratio increasing towards lower energies • p/p due to resonance decays, reproduced by UrQMD

  15. Critical point: fluctuations (II) • mean-pt (SpT) fluctuations rather constant • changing fluctuations of net electric charge ndyn? •  importance of resonance decays?! [CERES, NPA 727, 97 (2003)] [H. Appelshaeuser and H. Sako for CERES, nucl-ex/0409022]

  16. 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! r, w, f e+e- open charm event-by-event fluctuations detector requirements 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 • high speed DAQ and trigger ECAL (12 m) RICH magnet beam target TOF (10 m) STS (5, 10, 20, 40, 60, 80, 100 cm) TRDs (4,6, 8 m)

  18. TRD – tasks & challenge • Tasks: • electron identification, p suppression > 100 • tracking  global tracking, matching to STS, TOF (ECAL) • J/y meson, low-mass vector mesons • particle identification with TOF: (multi-)strange hadrons flow, correlations, fluctuations of identified particles • Challenge: • high counting rates (up to 100-150 kHz/cm2) • self triggered, fast readout (10 MHz) • large area (3 stations at 4,6,8,m  25, 50, 100 m2) • good position resolution (~200 mm)

  19. TRD – design • layers: radiator (foils or fibres/foams) + readout • MWPCs (ALICE) • GEMs • straw tubes (ATLAS) • Ongoing R&D! • design studies (segmentation, padsize, ordering,...) started: • 3-6 stations • 3 stations, 3 layers each • 3 stations, 4 layers each • 6 stations, 2 layers each

  20. TRD - simulation • simulation of TRDs (simplified geometry, (1.7 – 2.2) % X0) • e/p separation studied in dependence on • number of layers • thickness and compositions of the active gas • radiator parameters – foil & gap thickness

  21. CBM simulation framework • C++ based simulation framework in development for detailed detector simulation, feasibility studies, design optimization • tracking !

  22. Hybrids Strip MAPS Ultimate vertex resolution High resolution tracking With large coverage Should deliver unambiguous seeds STS tracking • set of silicon tracking stations inside magnetic field („heart of CBM“) • 2-3 vertex detectors with high resolution, minimum thickness (e.g. MAPS) • outer stations: Si-strip, (hybrid pixel detectors in addition?) optimization of layout started tracking!! so far: simple standard layout with 7 stations (3 + 4) in use

  23. STS tracking (II) Challenge: high track density  600 charged particles in  25o • 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)

  24. STS tracking (III) • several trackers under study (cellular automaton, Hough transform, conformal mapping, 3D track following) • problem: high hit densities: fakes, pile-up in MAPS? I. Kisel, CA, all tracks, NSTS > 3 ... including 10 pile-up events in MAPS

  25. TRD - tracking • standalone TRD - tracking  J/y trigger! • global tracking (standalone + matching, STS track extrapolation) • work has just started ... •  will finally lead to layout of detectors (padsize, station&layer ordering, ...) • pad layout used so far • rectangular pads: • 300-500 mm x 3-30 mm • odd layers rotated by 90°

  26. TRD – tracking (II) • track finding: STS track following • track fitting: Kalman filter • input: UrQMD events, central Au+Au @ 25 AGeV • Momentum distribution of tracks requiring > 4 hits in STS • hit rates 800-1000 per event per layer • large number of secondaries!

  27. TRD – tracking (III) • 9 layers in 3 stations, 2.2% X0 • efficiency for tracks with 9 TRD hits

  28. TRD – tracking (IV) • Compare to: • 12 layers in 3 stations, 2.2% X0 • efficiency for tracks with 12 TRD hits  slight improvement for low momenta! • connect to TOF hits: efficiency/ purity of PID? • impact on fluctuation measurements?

  29. data mixed events CBM: dynamical fluctuations UrQMD: central Au+Au collisions at 25 AGeV

  30. p-suppression 10-4 CBM: charmonium measurement e+e- e+e- channel (m+m- also under investigation) assumptions: ideal tracking momentum resolution 1% 2·1010 central Au + Au UrQMD 25 AGeV + GEANT3 different p-suppression, pt> 1 GeV p-suppression 10-4 10-2 10-3 10-4 • implement reconstructed tracks • PID no p (red)

  31. CBM:    → e+e- reconstructed PID reconstructed no PID track segment main problem: background e ! no tracking in field free region for rejection of close pairs!

  32. CBM:    → e+e- (II) • detailed study of cut strategies, still on ideal MC level

  33. CBM: m ? • alternative: measure J/y and low-mass vector mesons in m+m- channel? • 2 options studied: m detector behind TOF, rejection of m from p-decay via kink analysis (TRD!) • Fe/C absorbers behind STS, tracking stations in between + at end (TRD?) first promising results from kink studies for J/y! problem: m from r, w, f soft! also stopped ...

  34. CBM: D0→ K-p+ (~4%, ct = 124mm) • rather advanced studies available including tracking, secondary vertex reconstruction (65 mm resolution), cut strategies for online D selection (only tracking informnation from STS used, no PID) event reduction by factor 1000: 10 MHz  10 kHz D0+ D0 multiplicity from HSD: 1.5·10-4 per central Au+Au event at 25 AGeV

  35. CBM: D+ K-p+p+ (9%, ct = 317 mm) • first studies started, similar strategy as for D0 • feasibility of reconstructing 3 particle vertices shown • Lc (ct=62 mm,  pK-p+ (5%))? efficiency ~ 5.3%

  36. Outlook • detector design and optimization • R&D on detector components • feasibility studies of key observables • detailed studies started by now! • physics workshop, GSI Dec. 15th-16th, 2005 • CBM collaboration formed and still increasing • technical Status Report submitted in January 2005 • exciting physics lie ahead of us!

  37. CBM collaboration Croatia: RBI, Zagreb Cyprus: Nikosia Univ. Czech Republic: Czech Acad. Science, Rez Techn. Univ. Prague France: IReS Strasbourg Germany: Univ. Heidelberg, Phys. Inst. Univ. HD, Kirchhoff Inst. Univ. Frankfurt Univ. Mannheim Univ. Marburg Univ. Münster FZ Rossendorf GSI Darmstadt Romania: NIPNE Bucharest Russia: CKBM, St. Petersburg IHEP Protvino INR Troitzk ITEP Moscow KRI, St. Petersburg Kurchatov Inst., Moscow LHE, JINR Dubna LPP, JINR Dubna LIT, JINR Dubna PNPI Gatchina SINP, Moscow State Univ. Spain: Santiago de Compostela Univ. Ukraine: Univ. Kiev Hungaria: KFKI Budapest Eötvös Univ. Budapest Italy: INFN Frascati Korea: Korea Univ. Seoul Pusan National Univ. Norway: Univ. Bergen Poland: Jagiel. Univ. Krakow Silesia Univ. Katowice Warsaw Univ. Warsaw Tech. Univ. Portugal: LIP Coimbra

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