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Dielectron production in C+C collisions at 2AGeV with HADES

Dielectron production in C+C collisions at 2AGeV with HADES. Jochen Markert For the HADES Collaboration. Dielectron production in C+C collisions at 2AGeV with HADES. Reconstruction of the electron signal Results from C+C collisions at 2AGeV Comparison with models Comparison with DLS.

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Dielectron production in C+C collisions at 2AGeV with HADES

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  1. Dielectron production in C+C collisions at 2AGeV with HADES Jochen Markert For the HADES Collaboration

  2. Dielectron production in C+C collisions at 2AGeV with HADES • Reconstruction of the electron signal • Results from C+C collisions at 2AGeV • Comparison with models • Comparison with DLS Jochen Markert - QM 2006

  3. Opening angle > 9o Introduction C+C at 2AGeV • Large pair acceptance ~35% • Trigger • 1st level : charged particle mult. > 4 (60% reaction ) • 2nd level: RICH+TOF/PreSHOWER → enhancement ~10 • 9% dM/M resolution at 0.8 GeV/c2 Mee • Total statistic: 650 M 1st level events Averaged over 0 < Y < 2 Jochen Markert - QM 2006

  4. DATA Selection criteria Single e+,e- • Hit matching • RICH rings ↔ MDC tracks • MDC tracks ↔ TOF and PreShower hits • PID : e+, e- • β vs momentum correlation • PreShower condition • Background rejection cuts • Opening angle > 9° Jochen Markert - QM 2006

  5. Spectra before efficiency correction ~ 23000 signal pairs for full Mee range ~ 2000 signal pairs for full Mee > 150 MeV/c2 Jochen Markert - QM 2006

  6. Cocktail A: 0 + η + ω “long lived components“ • Cocktail B: Cocktail A + Δ + ρ 18 % 21 % Comparison of the data with cocktail • Event generatorPLUTO : • thermal source (T=80MeV) •  polar angle distribution from charged  analysis • η (TAPS data) • ρ, ω : m-scaling • Δ scales with  systematic errors: 15 % - efficiency correction 10 % - combinatorial background 11 % - 0 normalization Jochen Markert - QM 2006

  7. RQMD:M. D. Cozma, C. Fuchs, E. Santini, A. Faessler, Phys. Lett. B 640, 150 (2006) • UrQMD:D. Schumacher, S. Vogel, M. Bleicher, nucl-th/06080401. • HSD (v2.5):W. Cassing and E. L. Bratkovskaya, Phys. Rep. 308, 65 (1999). • Yield over Cocktail A • Cocktail B/ Cocktail A • factor 2 below data in 200< Mee <500 MeV/c2 • factor 4 below data in 500<Mee<650 MeV/c2 • Closer to data than cocktail B • But model calculations • Undershoot between 200<Mee<500 MeV/c2 • Overshoot for Mee> 700 MeV/c2 “free” spectral function Comparison of the data with models C+C at 2AGeV Jochen Markert - QM 2006

  8. η ω P┴ and Y distributionscomparison data vs. cocktail preliminary • Mee < 150 MeV/c2 :Data well described (0-Dalitz region) • 150 < Mee < 550 MeV/c2 :Underestimation over whole p range (factor 2). Jochen Markert - QM 2006

  9. DLS HADES η F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys) F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys) Comparison of C+C of DLS(1.04AGeV) and HADES(2.0AGeV) R. J. Porter et al., Phys. Rev. Lett. 79 1229 (1997) Enhancement factor F over ηfor 150<Mee<500 MeV/c2 : Jochen Markert - QM 2006

  10. R. Averbeck et al., TAPS coll., Z. Phys. A 359, 65 (1997) • R. Holzmann et al., TAPS coll., Phys. Rev. C 56, R2920 (1997) DLS η Yexc(2.0)/Yexc(1.04) = 2.5 ± 0.5(stat) ± 1.5(sys) Comparison of C+C of DLS(1.04AGeV) and HADES(2.0AGeV) DLS F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys) HADES F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys) Jochen Markert - QM 2006

  11. TAPS, KaoS measurements: Excess yield : Excess yield scales like 0 ! A closer look to the excess yield Jochen Markert - QM 2006

  12. C+C at 1 AGeV (HADES)before efficiency correction • Spectrum before efficiency correction • Enhancement factor F(1.0) ≈ 5.8 (in 150<Mee<500 MeV/c2 range) • Enhancement within errors in agreement with DLS HADES preliminary Jochen Markert - QM 2006

  13. Summary & outlook OutLook • Ongoing analysis of • p+p at 2.2 GeV (Jan. 04)  exp. check of η reconstruction eff. • C+C at 1 AGeV (Aug. 04)  direct comparison with DLS • Ar+KCl at 1.757 AGeV (Sep. 05) • p+p at 1.25 GeV (Jan. 06)  Δ production • Next physics runs • p/d+p, at 3.5/1.25 AGeV (Spring. 07)  ω production/isospin dependence • p+A (2007+) • Heavy systems, pion beam (2008/9) Summary • 2 AGeV C+C dielectron spectra • excess yield established • no specific pdependence for enhancement • Comparison to models ongoing • Comparison to DLS: • Preliminary 1 AGeV spectra shows no contradiction to DLS data • Excess of yield for 150<Mee<500 MeV/c2 measured at 1.04 and 2 AGeV scales like 0 multiplicity Jochen Markert - QM 2006

  14. The HADES collaboration • Bratislava (SAS, PI), Slovakia • Catania (INFN - LNS), Italy • Cracow (Univ.), Poland • Darmstadt (GSI), Germany • Dresden (FZD), Germany • Dubna (JINR), Russia • Frankfurt (Univ.), Germany • Giessen (Univ.), Germany • Milano (INFN, Univ.), Italy • Munich (TUM), Germany • Moscow (ITEP,MEPhI,RAS), Russia • Nicosia (Univ.), Cyprus • Orsay (IPN), France • Rez (CAS, NPI), Czech Rep. • Sant. de Compostela (Univ.), Spain • Valencia (Univ.), Spain • Coimbra (Univ.), Portugal Jochen Markert - QM 2006

  15. The END Thank you for your attention

  16. Pluto vs Hades data preliminary Hades@GSI and DLS@LBL • design • π0, η acceptance • C+C @ 1AGeV • Comparison with Pluto cocktail π0→e+e–γ η→e+e–γ Hades DLS Hades DLS mid-rapidity mid-rapidity Jochen Markert - QM 2006

  17. Phase space coverage: HADES vs DLS π0→e+e–γ η→e+e–γ • A direct Comparison between HADES and DLS dielectron results not feasible Jochen Markert - QM 2006

  18. Efficiency corrections Efficiency matrix is created for single leptons (e+, e-) in p (0 – 2 GeV/c), Θ (0o – 90o), Φ (0o – 360o) averaged over momentum averaged over all sectors Jochen Markert - QM 2006

  19. Acceptance matrix Acceptance matrix is created in p (0 – 2 GeV/c), Φ (0o – 60o), Θ (0o – 90o) for the single leptons. Integrating over internal dilepton angle → Pair acceptance matrix: Mee, PT and Y Jochen Markert - QM 2006

  20. Acceptance matrix is created in p (0 – 2 GeV/c), Φ (0o – 60o) and Θ (0o – 90o) for the single leptons. • Integrating over internal dilepton angle one can create pair acceptance matrix in 3D: Mee, PT and Y Opening angle > 9o Acceptance matrix Jochen Markert - QM 2006

  21. Experiment Simulation Theory Event Generator Physics AcceptanceFilter HADES Detector Simulation dN/dM RawData Monte-Carlo Data Analysis Analysis Efficiency Correction PairSpectra Pair Spectra Analysis flow Jochen Markert - QM 2006

  22. Events 46% - LVL2 60% - LVL1 242 M - recorded events 217 M – trigger M4 events 6 % of LVL1 events are also LVL2 Days of data taking Evaluation of the statistics • all files • all good files • only M4 events • only events with >=1 track Jochen Markert - QM 2006

  23. UrQMD σgeom - Π b2max σtot 6 4 2 impact parameter [fm] σreac σtrigger * in agreement with Kox et all. 864 ± 45 mbarn LVL1 trigger - centrality selection Jochen Markert - QM 2006

  24. Normalization factor • respective number of LVL1 events * DS factor : 6.5 ● 108 • 0multiplicity extrapolated into 4Π : 1.15 • efficiency of the LVL2 trigger : 0.92 Jochen Markert - QM 2006

  25. 1 m The spectrometer concept • During run in November 2002 • RICH, inner MDC’s, TOF and SHOWER ready • outer MDC’s only partly installed • In analysis presented here only inner MDC’s are used • Geometry • Full azimuth, polar angles 18o - 85o • Pair acceptance  0.35 • About 80.000 detector channels • Particle identification • RICH: CsI solid photo cathode, C4F10 radiator, No  80, pion suppression  104 • TOF: 384 scintillator rods • TOFino: 24 scintillator paddles temporary solution, RPC in future • Pre-Shower: 18 pad chambers & lead converters) • Momentum measurement • Magnet: superconducting Toroid with Br = 0.36 Tm • MDC: 24 multi-wire drift chambers, single-cell resolution  140 mm Jochen Markert - QM 2006

  26. Lepton multiplicity per event • ~7% of the events contain 2 opposite sign leptons • ~7% of the events contain 2 like sign leptons • ~83% of the events contain only 1 lepton Jochen Markert - QM 2006

  27. Simulation p*q [MeV/c] Single leptons: Efficiency and Purity Efficiency:  80% Purity:  85% Contamination: • lepton fakes  15% (mainly close pairs) • hadrons < 3% Jochen Markert - QM 2006

  28. Relative suppression C1 C2 C3 Background rejection <9o TOF/Shower <90 MDC I-II RICH C1 C2 C3 close conversion candidate Shared detector hit Close pair C1 – the only pair cut C2, C3 – lepton cuts Jochen Markert - QM 2006

  29. Combinatorial background same event Like-Sign (sLS) vs. mixed event Opposite-Sign (mOS) Mee > 150MeV/c2 combinatorial background: M < 150 MeV/c2 - sLS M > 150 MeV/c2 - mOS • Normalization done between 150-550 MeV/c2 Mee • sLS and mOS background show same behavior for Mee > 150 MeV/c2 Mee > 150MeV/c2 Jochen Markert - QM 2006

  30. 18 % 21 % Summary of the eff corrections, normalization and systematic errors • Components for the efficiency corrections: • efficiency correction • opening angle correlation • tracking efficiency – 92% for each singles • Components for the normalization: • number of LVL1 * DS events • second level trigger (LVL2) efficiency – 92% • 0 multiplicity into 4 - 1.15 • Components for the systematic errors: • 15 % - efficiency correction (self-consistence check) • 10 % - combinatorial background • 11 % - 0 normalization Jochen Markert - QM 2006

  31. combinatorial background efficiency corrections at maximum 15% at maximum 10% Estimation of the systematic errors • Normalization to 0 multiplicity • 11 % systematic error comes from: • efficiency/purity corrections • extrapolation to 4, full momenta Jochen Markert - QM 2006

  32. THEORY SIMULATION Self-consistency check of efficiency correction Pluto data through HADES acceptance filter Pluto data through reconstruction chain and efficiency correction Jochen Markert - QM 2006

  33. Yexc(2.0)/Yexc(1.04) = 2.5 ± 0.5(stat) ± 1.5(sys) Comparison of C+C of DLS(1.04AGeV) and HADES(2.0AGeV) F(1.04) = 6.5 ± 0.5(stat) ± 2.1(sys) F(2.0) = 2.07 ± 0.21(stat) ± 0.38(sys) Jochen Markert - QM 2006

  34. η ω P┴ and Y distributionscomparison Data vs. PLUTO Good agreement for the low masses ! No strong P┴ dependence for enhancement ! Jochen Markert - QM 2006

  35. in-medium Comparison of the data with models • RQMD Tübingen C.Fuchs, D. Cozma • HSD Gießen (v2.5) E. Bratkovskaya, W. Cassing • In-medium calculation • Undershoot between 200<Mee<500 MeV/c2 (HSD) • Overshoot between 450<Mee<600 MeV/c2 (RQMD) Jochen Markert - QM 2006

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