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Dielectron production in C+C collisions at 2AGeV with HADES Jochen Markert For the HADES Collaboration
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Jochen Markert - QM 20062 19 - November - 2006 Reconstruction of the electron signal Results from C+C collisions at 2AGeV Comparison with models Comparison with DLS Dielectron production in C+C collisions at 2AGeV with HADES
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Jochen Markert - QM 20063 19 - November - 2006 Introduction C+C at 2AGeV Large pair acceptance ~35% Trigger 1 st level : charged particle mult. > 4 (60% reaction ) 2 nd level: RICH+TOF/PreSHOWER → enhancement ~10 9% dM/M resolution at 0.8 GeV/c 2 M ee Total statistic: 650 M 1 st level events Opening angle > 9 o Averaged over 0 < Y < 2
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Jochen Markert - QM 20064 19 - November - 2006 Selection criteria 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° DATA Single e +,e -
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Jochen Markert - QM 20065 19 - November - 2006 Spectra before efficiency correction 23000 ~ 23000 signal pairs for full M ee range 2000 ~ 2000 signal pairs for full M ee > 150 MeV/c 2
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Jochen Markert - QM 20066 19 - November - 2006 Event generator PLUTO : thermal source (T=80MeV) polar angle distribution from charged analysis η (TAPS data) ρ, ω : m -scaling Δ scales with Comparison of the data with cocktail 18 % 21 % systematic errors: 15 % - efficiency correction 10 % - combinatorial background 11 % - 0 normalization Cocktail A: 0 + η + ω “long lived components“ Cocktail B: Cocktail A + Δ + ρ
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Jochen Markert - QM 20067 19 - November - 2006 Yield over Cocktail A Cocktail B/ Cocktail A factor 2 below data in 200< M ee <500 MeV/c 2 factor 4 below data in 500< M ee < 650 MeV/c 2 Comparison of the data with models 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). “free” spectral function Closer to data than cocktail B But model calculations Undershoot between 200<M ee <500 MeV/c 2 Overshoot for M ee > 700 MeV/c 2 C+C at 2AGeV
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Jochen Markert - QM 20068 19 - November - 2006 P ┴ and Y distributions comparison data vs. cocktail ω η M ee < 150 MeV/c 2 : Data well described ( 0 -Dalitz region) 150 < M ee < 550 MeV/c 2 : Underestimation over whole p range (factor 2). preliminary
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Jochen Markert - QM 20069 19 - November - 2006 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) HADES DLS η Enhancement factor F over η for 150<M ee <500 MeV/c 2 : R. J. Porter et al., Phys. Rev. Lett. 79 1229 (1997)
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Jochen Markert - QM 200610 19 - November - 2006 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) Y exc (2.0)/Y exc (1.04) = 2.5 ± 0.5(stat) ± 1.5(sys) DLS HADES η DLS R. Averbeck et al., TAPS coll., Z. Phys. A 359, 65 (1997) R. Holzmann et al., TAPS coll., Phys. Rev. C 56, R2920 (1997)
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Jochen Markert - QM 200611 19 - November - 2006 A closer look to the excess yield TAPS, KaoS measurements: Excess yield : Excess yield scales like 0 !
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Jochen Markert - QM 200612 19 - November - 2006 C+C at 1 AGeV (HADES) before efficiency correction HADES preliminary Spectrum before efficiency correction Enhancement factor F(1.0) ≈ 5.8 (in 150<M ee <500 MeV/c 2 range) Enhancement within errors in agreement with DLS
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Jochen Markert - QM 200613 19 - November - 2006 Summary & outlook 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<M ee <500 MeV/c 2 measured at 1.04 and 2 AGeV scales like 0 multiplicity 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)
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Jochen Markert - QM 200614 19 - November - 2006 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
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The END Thank you for your attention
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Jochen Markert - QM 200616 19 - November - 2006 Hades@GSI and DLS@LBL design π 0, η acceptance C+C @ 1AGeV Comparison with Pluto cocktail preliminary Pluto vs Hades data π 0 π 0 →e + e – γ Hades DLS DLS mid-rapidity η→e + e – γ Hades DLS DLS mid-rapidity
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Jochen Markert - QM 200617 19 - November - 2006 Phase space coverage: HADES vs DLS A direct Comparison between HADES and DLS dielectron results not feasible π 0 π 0 →e + e – γ η→e + e – γ
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Jochen Markert - QM 200618 19 - November - 2006 Efficiency corrections Efficiency matrix is created for single leptons (e+, e - ) in p (0 – 2 GeV/c), Θ (0 o – 90 o ), Φ (0 o – 360 o ) averaged over momentum averaged over all sectors
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Jochen Markert - QM 200619 19 - November - 2006 Acceptance matrix Acceptance matrix is created in p (0 – 2 GeV/c), Φ (0 o – 60 o ), Θ (0 o – 90 o ) for the single leptons. Integrating over internal dilepton angle → Pair acceptance matrix: M ee, P T and Y
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Jochen Markert - QM 200620 19 - November - 2006 Acceptance matrix Opening angle > 9 o Acceptance matrix is created in p (0 – 2 GeV/c), Φ (0 o – 60 o ) and Θ (0 o – 90 o ) for the single leptons. Integrating over internal dilepton angle one can create pair acceptance matrix in 3D: M ee, P T and Y
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Jochen Markert - QM 200621 19 - November - 2006Experiment RawData Raw Data HADES Analysis Physics PairSpectra Pair SpectraSimulation Monte-Carlo Data Detector Simulation Analysis Event Generator Pair Spectra Efficiency Correction Correction dN/dM AcceptanceFilter Acceptance Filter Theory Analysis flow
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Jochen Markert - QM 200622 19 - November - 2006 Days of data taking Events all files all good files only M4 events only events with >=1 track Evaluation of the statistics 242 M - recorded events 217 M – trigger M4 events 6 % of LVL1 events are also LVL2 46% - LVL2 60% - LVL1
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Jochen Markert - QM 200623 19 - November - 2006 UrQMD impact parameter [fm] 4 6 2 σ tot σ reac σ trigger LVL1 trigger - centrality selection σ geom - Π b 2 max * in agreement with Kox et all. 864 ± 45 mbarn
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Jochen Markert - QM 200624 19 - November - 2006 Normalization factor NOV02 Yield/event0.79HADES acceptance – LVL1 trigger Correction to 4Π1.44 Yield corr to 4Π1.15 Corr. to trigger0.714Π – LVL1 trigger Min. bias yield0.814Π min. bias 6.5 ● 10 8respective number of LVL1 events * DS factor : 6.5 ● 10 8 1.15 0 multiplicity extrapolated into 4Π : 1.15 0.92efficiency of the LVL2 trigger : 0.92
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Jochen Markert - QM 200625 19 - November - 2006 The spectrometer concept Geometry Full azimuth, polar angles 18 o - 85 o Pair acceptance 0.35 About 80.000 detector channels Particle identification RICH: CsI solid photo cathode, C 4 F 10 radiator, N o 80, pion suppression 10 4 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 B = 0.36 Tm MDC: 24 multi-wire drift chambers, single-cell resolution 140 m 1 m 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
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Jochen Markert - QM 200626 19 - November - 2006 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
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Jochen Markert - QM 200627 19 - November - 2006 Efficiency: 80% Purity: 85% Contamination: lepton fakes 15% (mainly close pairs) hadrons < 3% Single leptons: Efficiency and Purity Simulation p*q [MeV/c]
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Jochen Markert - QM 200628 19 - November - 2006 Background rejection C1 C1 – the only pair cut C2C3 C2, C3 – lepton cuts TOF/Shower <9 o RICH MDC I-II C1 C2 C3 C1 C2 C3 <9 0 Close pair Shared detector hit close conversion candidate Relative suppression C1 C2 C3
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Jochen Markert - QM 200629 19 - November - 2006 combinatorial background: M < 150 MeV/c 2 - sLS M > 150 MeV/c 2 - mOS M ee > 150MeV/c 2 Combinatorial background same event Like-Sign (sLS) vs. mixed event Opposite-Sign (mOS) Normalization done between 150-550 MeV/c 2 M ee sLS and mOS background show same behavior for M ee > 150 MeV/c 2
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Jochen Markert - QM 200630 19 - November - 2006 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 18 % 21 %
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Jochen Markert - QM 200631 19 - November - 2006 Estimation of the systematic errors efficiency corrections at maximum 15% combinatorial background at maximum 10% Normalization to 0 multiplicity 11 % systematic error comes from: efficiency/purity corrections extrapolation to 4, full momenta
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Jochen Markert - QM 200632 19 - November - 2006 Self-consistency check of efficiency correction SIMULATION THEORY Pluto data through HADES acceptance filter Pluto data through reconstruction chain and efficiency correction
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Jochen Markert - QM 200633 19 - November - 2006 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) Y exc (2.0)/Y exc (1.04) = 2.5 ± 0.5(stat) ± 1.5(sys)
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Jochen Markert - QM 200634 19 - November - 2006 P ┴ and Y distributions comparison Data vs. PLUTO Good agreement for the low masses ! No strong P ┴ dependence for enhancement ! ω η
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Jochen Markert - QM 200635 19 - November - 2006 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<M ee <500 MeV/c 2 (HSD) Overshoot between 450<M ee <600 MeV/c 2 (RQMD) in-medium
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