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Strasbourg 2006

Strasbourg 2006. Low Mass Lepton Pairs Experiments Joachim Stroth, Univ. Frankfurt, GSI. Motivation. l +. First chance collisions. r. l -. Dense matter. Freeze-out. VMD. The dilepton signal contains contributions from throughout the collision , ..

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Strasbourg 2006

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  1. Strasbourg 2006 Low Mass Lepton Pairs Experiments Joachim Stroth, Univ. Frankfurt, GSI

  2. Motivation l+ First chance collisions r l- Dense matter Freeze-out VMD • The dilepton signal contains contributions from throughout the collision, .. • ... i.e. also direct radiation from the early phase. • It probes the electromagnetic structure of dense/hot nuclear(or partonic) matter. Joachim Stroth

  3. Motivation (Chiral Symmetry Restoration) SIS 18 SIS 300 SPS SIS 18 SIS 300 SPS SIS 18 SIS 300 SPS freeze-out regions S. Leupold, Trento Workshop 2005 J. Wambach et al. • Substantial depletion of the condensates already in collisions at moderate beam energy. 2-quark condensate 4-quark condensate Joachim Stroth

  4. Experimental strategy • AA collisions • Radiation from the dense/hot phase • Identify/subtract combinatorial background • Identify/subtract contributions from late hadron decays • p,p,g on A • Modification of (w,f) spectral functions • High resolution • elementary reactions • gain knowledge on production mechanisms Joachim Stroth

  5. VM modification in reactions on nuclei KEK: • proton induced reactions. • r drops10% but no broadening TAPS/ELSA: • Photoproduction • w is broadened (G~ 90 MeV) and dropping Joachim Stroth

  6. Overview Alice LHC IT HPID RHIC SPS CERES TPC SIS300 SIS 100AGS upgrade SIS18 Bevalac time (technological advance) Joachim Stroth

  7. The HADES experiment @ GSI • f symmetry • hadron blind RICH • 2 % mass resolution (10% without outer tracking) Joachim Stroth

  8. C+C 2AGeV: e+e- invariant mass spectrum signal < 140 MeV/c2: 20971 counts signal > 140 MeV/c2: 1937 counts ~ 100 M electron trigger e+ e- pairs measured over 5 orders of magnitude Joachim Stroth

  9. HADES data 2 AGeV C+C e+e- signal pairs hadronic cocktail (PLUTO generator) 2 AGeV C+C e+e- signal pairs hadronic cocktil (PLUTO generator) factor 2.5 • Electron pair yield observed in acceptance • Corrected for reconstruction efficiency • PLUTO (thermal) event generator: yields from TAPS measurement and using mt scaling. Joachim Stroth

  10. C+C 2AGeV:Comparison to transport Conventional sources under control Vacuum spectral functions Differences in the description of D's and VM's Joachim Stroth

  11. C+C 1AGeV: HADES data (preliminary) 1 AGeV C+C e+e- signal pairs hadronic cocktail (PLUTO generator) factor 5 • Electron pair yield observed in acceptance • Corrected for reconstruction efficiency • Substantial yield above the h contribution preliminary Joachim Stroth

  12. The DLS spectrometer @ LBL HADES DLS mid-rapidity Joachim Stroth

  13. DLS and RQMD (Tübingen Group) The puzzle remains C. Fuchs et al. Joachim Stroth

  14. Comparison with the DLS results • systematic errors • data (CB subtraction) • simplified event generator • (only π,η) • angular distributions • generated events processed by the full • HADES analysis including: • detector (in)efficiency • reconstruction (in)efficiency Joachim Stroth

  15. The CERES Spectrometer @ CERN CERES • f symmetry • dE/dX in silicon drift for background rejection • 3.8 % mass resolution (TPC upgrade) Joachim Stroth

  16. CERES data Rapp/Wamb. med. r Rapp/Wamb.drop. r Kämpfer qqbar CERES No substantial 'hole" between w and f pole mass J. Stachel, ISHIP 2006 and nucl-ex/0511010 Joachim Stroth

  17. The NA60 spectrometer @ CERN • High resolution tracking by means of silicon (pixel) detectors. Mass resolution = 2.3 % (f) • Challenge: • Track matching through absorber • Match in configuration and momentum space Joachim Stroth

  18. NA60 acceptance Gain in statistics over CERES > 1000 S. Damjanovic, Hot Quarks 2006 Joachim Stroth

  19. NA60 systematic uncertainties S. Damjanovic, Hot Quarks 2006 Joachim Stroth

  20. NA60 centrality dependence Can this help to reduce uncertainties in the fireball evolution (surface effects) S. Damjanovic, Asilomar 2006 Joachim Stroth

  21. NA60: pT Spectra different mass bins comparison to theory S. Damjanovic, Asilomar 2006 Joachim Stroth

  22. LMLP in PHENIX @ RHIC p DC e+ e- PC1 magnetic field & tracking detectors PC3 S/B between 10-2 – 10-3 S/B will get much better once the HPID is operational A. Toja, Hot Quarks 2006 Joachim Stroth

  23. From HADES to CBM @ FAIR CBM 8 – 45 AGeV HADES 2 – 8 AGeV Joachim Stroth

  24. Dielectron reconstruction in CBM Full Track Track Segment C B M fake pair Track Fragment • Fast, high-precision tracking using silicon sensors. • No electron identification before tracking Joachim Stroth

  25. Background rejection performance C B M accepted after cuts applied More than two orders suppression bg π0 bg       • Au+Au 25 AGeV, central collisions • Signal mixed into UrQMD events T. Galatyuk, CBM coll. meeting 2005 Joachim Stroth

  26. The muon option in CBM C B M J/ψ→μ+μ- s/b ~ 100 C/Fe absorbers + detector layers • Simulation Au+Au 25 AGeV: • Excellent signal to background ratio in high mass region. • Low efficiency for small invariant masses and/or low pT (enhancement region). • Challenging muon detector (high particle densities) ρ ω φ A. Kiseleva, Y.Vassiliev Joachim Stroth

  27. Challenges for next generation experiments • Improve characterization • Double differential (e.g. inv. mass, pt) • Centrality dependence • Reduce uncertainties • Statistical errors • Fast detectors and DAQ • Develop a trigger (not always easy, excellent detectors needed) • Systematical errors • Control combinatorial background (good background rejection) • Fully understand efficiencies of detectors, track reconstruction, rejection cuts • Good to know before design freeze-out • What precision is really needed to distinguish between scenarios? • Can one control uncertainties due to missing information about the fireball evolution? Joachim Stroth

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